Primary peritoneal clear cell carcinoma with metastasis mimicking ovarian carcinoma: A case report and literature review

Primary peritoneal clear cell carcinoma with metastasis mimicking ovarian carcinoma: A case report and literature review | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Case Report Primary peritoneal clear cell carcinoma with metastasis mimicking ovarian carcinoma: A case report and literature review Nah Ihm Kim, Ji Shin Lee, Kyung-Hwa Lee, Sung Sun Kim This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-8103498/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 07 Feb, 2026 Read the published version in Journal of Ovarian Research → Version 1 posted 10 You are reading this latest preprint version Abstract Background Primary peritoneal clear cell carcinoma (PPCCC) is an exceptionally rare malignancy that closely resembles gynecologic epithelial cancers clinically and histologically. Its pathogenesis is poorly understood, with possible origins from Müllerian metaplasia or malignant transformation of endometriosis. Case presentation A 48-year-old woman with no history of endometriosis or hormone therapy presented with acute lower abdominal pain. Imaging revealed a pelvic mass and a lesion in the pancreatic tail. The patient underwent hysterectomy with bilateral salpingo-oophorectomy and distal pancreatectomy with splenectomy. Intraoperatively, the pelvic mass was located in the peritoneum, while the gynecologic organs appeared grossly normal. Histopathologic examination of the pelvic, pancreatic, and splenic lesions revealed identical features of clear cell carcinoma. Immunohistochemistry demonstrated positivity for PAX8, CK7, and HNF1β, with loss of MSH2 and MSH6. Next-generation sequencing revealed ARID1A loss and somatic PIK3CA mutations. No primary ovarian, endometrial, or renal tumor was detected, supporting a diagnosis of primary peritoneal clear cell carcinoma with metastases to the pancreas and spleen. Conclusions This case highlights the diagnostic challenges of PPCCC and offers valuable insights into the clinical and pathological spectrum of this underrecognized malignancy. Primary peritoneum carcinoma Clear cell carcinoma Endometriosis Figures Figure 1 Figure 2 Figure 3 Background Primary peritoneal clear cell carcinoma (PPCCC) is an exceptionally rare malignancy that closely resembles gynecologic epithelial cancers both clinically and histologically. While clear cell carcinoma (CCC) most commonly arises in the ovary or endometrium, its occurrence as a primary tumor in the peritoneum is exceedingly uncommon. Since its first description in 1990 ( 1 ), only a limited number of cases have been reported in the English literature ( 2 – 15 ). Diagnosing PPCCC is challenging due to its overlapping morphological features with more common neoplasms originating from the ovary, endometrium and kidney. The pathogenesis of PPCCC remains poorly understood, though current hypotheses suggest possible origins from Müllerian metaplasia or malignant transformation of endometriosis ( 11 ). However, many reported cases, including the present one, lack histological evidence of endometriosis or hormonal influence ( 1 , 2 , 7 , 9 , 11 , 13 – 15 ). Given the rarity of reported cases, each new case provides valuable insights into the clinical and pathological spectrum of this underrecognized malignancy. Herein, we present a case of PPCCC in a 49-year-old woman without a history of endometriosis or hormone therapy, underscoring the diagnostic complexity and clinical significance of this unusual tumor. Case presentation A 48-year-old woman with no significant past medical or family history presented to a local clinic with acute lower abdominal pain. She had no prior history of hormone replacement therapy or endometriosis. Laboratory tests revealed elevated tumor markers, including CA 19-9 (777.3 U/mL) and CA 125 (242.9 U/mL), while CEA (1.3 ng/mL) and AFP (3.06 ng/mL) were within normal limits. Abdominal computed tomography (CT) revealed a 15×10 mm oval-shaped, subtly enhancing lesion in the pancreatic tail, raising suspicion for either pancreatic adenocarcinoma or an islet cell tumor. Additionally, a 70×65×35 mm well-defined, heterogeneously enhancing solid mass was noted in the left pelvic cavity, suspicious for a malignant pelvic tumor or metastasis. The patient was referred to a tertiary care center for further evaluation. Upon transfer, pelvic magnetic resonance imaging (MRI) revealed an 11 cm mixed cystic and solid mass in the left adnexa, with the solid component demonstrating heterogeneous enhancement and diffusion restriction, suggestive of ovarian malignancy (Figure 1). Under the clinical impression of synchronous ovarian and pancreatic malignancies, the patient underwent total abdominal hysterectomy with bilateral salpingo-oophorectomy and distal pancreato-splenectomy. Intraoperatively, a large pelvic mass was identified within the pelvic peritoneum. Frozen section analysis performed during surgery initially suggested high-grade serous carcinoma of ovarian origin. A 2 cm encapsulated, well-demarcated mass was also identified in the pancreatic tail, adherent to the adjacent omentum, requiring adhesiolysis. However, both ovaries, fallopian tubes, and uterus appeared grossly unremarkable. Figure 1. Pelvic MRI demonstrating a large mixed cystic and solid mass in pelvic cavity. (A) Sagittal view. (B) Coronal view showing heterogeneous enhancement and diffusion restriction within the solid component, suggestive of malignancy. Gross pathological examination revealed a 12×11×3.5 cm pelvic mass with no apparent lesions in other gynecologic organs. The pancreatic tail contained a 3×2.8×2.5 cm cystic lesion with a friable whitish intraluminal mass. A 1.3×1.1 cm cystic lesion was also observed in the spleen. Microscopically, the pancreatic, splenic, and pelvic masses shared identical histomorphological features, characterized by solid and papillary architecture with focal necrosis. Tumor cells displayed round to oval nuclei with irregular contours, clear to eosinophilic cytoplasm, and moderate nuclear atypia. Mitotic activity was variable, and occasional eosinophilic hyaline globules were noted (Figure 2). No lymphovascular or perineural invasion was noted. The specimens also lacked any histologic features suggestive of endometriosis, such as endometrial glands, stroma, or hemosiderin-laden macrophages. Immunohistochemical staining showed positivity for PAX8, CK7, and HNF1β, and negativity for CK20, p16, WT1, and calretinin. p53 staining revealed a wild-type expression pattern. DNA mismatch repair (MMR) immunostaining demonstrated loss of nuclear expression of MSH2 and MSH6, while MLH1 and PMS2 remained intact, indicating MMR deficiency (Figure 3). To exclude a gynecologic origin of the clear cell carcinoma, the ovaries, fallopian tubes, and uterus were serially and thoroughly sectioned for microscopic examination. However, no evidence of a primary tumor was identified. Next generation sequencing (NGS) of the tumor revealed loss of ARID1A, along with additional somatic mutations in PIK3CA H1047R and PIK3CA Q546L. Discussion Figure 2. Gross specimens of the resected tumors. (A) Pancreas: Well-demarcated mass measuring approximately 2 cm, with solid and cystic components and hemorrhage. (B) Pelvic mass: Irregularly shaped solid mass with a lobulated and uneven surface (C) Uterus and adnexa: Both ovaries and fallopian tubes appeared grossly unremarkable, except for a leiomyoma in the uterus; no primary tumor was identified. Figure 3. Histopathologic and immunohistochemical features of the peritoneal clear cell carcinoma. (A) Low-power view showing a predominantly solid and papillary architecture with necrosis (H&E, ×20). (B) High-power view demonstrating tumor cells with round to oval nuclei, clear to eosinophilic cytoplasm and moderate nuclear atypia (H&E, ×100). (C,D) Tumor cells show diffuse positivity for PAX8 (C,×100) and HNF1β (D, ×100). (E,F) DNA mismatch repair analysis demonstrates retained MLH1 expression (E, ×100) but loss of MSH2 nuclear staining (F, ×100), indicating MMR deficiency. Based on intraoperative findings, histopathological features, immunohistochemical profile and molecular characteristics by NGS, the final diagnosis was primary peritoneal clear cell carcinoma, with metastases to the pancreas and spleen, a highly unusual presentation. The patient was diagnosed with stage IVB primary peritoneal clear cell carcinoma, and the case was discussed at a multidisciplinary tumor board to determine the appropriate adjuvant treatment. The patient is scheduled to undergo six cycles of chemotherapy with gemcitabine and carboplatin. Discussion Primary peritoneal carcinoma (PPC) is a rare epithelial malignancy that arises from the peritoneal lining, with diagnostic criteria established by the Gynecologic Oncology Group (GOG) (16). According to these criteria, PPC can be diagnosed when both ovaries are either normal in size or only benignly enlarged, and when the extent of peritoneal involvement exceeds that of the ovarian surface. Primary peritoneal clear cell carcinoma (PPCCC) represents an exceedingly rare histologic subtype of PPC, accounting for approximately 3% of cases (17). Histologically, it is indistinguishable from clear cell carcinomas (CCCs) of Müllerian origin, particularly those of the ovary and endometrium. Therefore, meticulous exclusion of other primary sites is essential for establishing a diagnosis. In the present case, serial sectioning and detailed histopathologic evaluation of the uterus, ovaries, and fallopian tubes revealed no evidence of a primary tumor, thereby fulfilling the GOG criteria for PPC and supporting a diagnosis of PPCCC. While the pathogenesis of PPCCC remains poorly understood, the most widely accepted hypotheses suggest either Müllerian metaplasia or malignant transformation of endometriosis (11). However, extraovarian malignant transformation of endometriosis is extremely rare, occurring in only 1.6% of cases (18). In previous reports, approximately one-third of patients with PPCCC had a history of endometriosis, and endometriotic foci were often found histologically (10, 17). In our case, however, extensive histologic sampling failed to demonstrate any features of endometriosis, such as endometrial-type glands or stroma, or hemosiderin-laden macrophages. A review of previously reported PPCCC cases is summarized in Table 1, providing an overview of Table 1. Literature review for cases of clear cell carcinoma of peritoneum Authors Age Tumor location Endometriosis Treatment Outcome Molecular characteristics Evans et al. (26) 54 Sigmoid mesocolon Yes DS + RT NA NA Lee et al. (1) 67 Pelvic cavity No DS + TAHBSO NA NA Tziortzioti et al. (7) 62 Peritoneum and omentum No DS + TAHBSO + OM + CT DOD at 6 mo NA Ichimura et al. (6) 45 Pelvic cavity Yes DS + TAHBSO + CT ROD at 32 mo NA Hama et al. (5) 53 Peritoneum Yes DS + BSO + CT DOD at 5 mo NA Terada et al. (13) 49 Gastric peritoneal, splenic hilus No DS NED at 6 mo NA Takano et al. (14) 53 Upper abdomen and omentum No DS + CT DOD at 5 mo NA Takano et al. (14) 66 Omentum and peritoneum No DS + TAHBSO + OM + LND + CT NED at 20 mo NA Matsuo et al. (4) 37 Abdominal scar Yes DS + CT ROD at 18 mo NA Muezzinoglu et al. (3) 54 Abdomen Yes DS + TAHBSO + CT NED at 12 mo NA Johnson et al. (2) 54 Proximal vagina and vaginal cuff No CT + RT ROD at 4 mo NA Shigeta et al. (10) 59 Douglas pouch Yes DS + TAHBSO + LND + CT NED at 5 mo NA Peiro et al. (11) 48 Peritoneum No TAHBSO + OM + CT NED at 28 mo ARID1A loss Giannakopoulos et al. (15) 61 Peritoneum No DS NED at 2 mo Alves et al. (9) 34 Peritoneum No TAH + LND + OM + CT DOD at 24 mo BRCA1A unknown significance Present case 48 Pelvic peritoneum No TAHBSO + CT NED at 1 mo ARID1A loss PIK3CA H1047R patient demographics, tumor location, history of endometriosis, molecular findings and clinical outcomes. Most cases involved women in their 40s to 60s, with endometriosis present in only a subset of cases, reflecting the heterogeneous pathogenesis of this malignancy. Our case shares similar histopathologic features but is distinguished by DNA mismatch repair deficiency and ARID1A loss on NGS, highlighting both overlapping and unique molecular characteristics. The differential diagnosis of CCC arising in the peritoneum includes high-grade serous carcinoma, malignant mesothelioma, and metastatic clear cell carcinomas from other organs, particularly the kidney. High-grade serous carcinoma is characterized by marked nuclear atypia, frequent mitotic figures, and a complex papillary or solid architecture (19). In contrast, malignant mesothelioma often demonstrates relatively bland cytologic features and simple papillary formations lined by a single layer of uniform mesothelial cells. Despite morphologic overlap with CCC, these entities can usually be distinguished through a combination of histologic evaluation and imunohistochemical profiling. Among metastatic tumors, clear cell renal cell carcinoma (CCRCC), is an important consideration. CCRCC typically displays a nested-alveolar growth pattern with rich stromal vasculature, whereas Müllerian-type CCC is characterized by tubulocystic architecture, small rounded papillae, and hobnail cells (20). Immunohistochemically, CCRCC is frequently negative for CK7, HNF1 beta, whereas CCCs of gynecologic origin are typically positive for these markers. In our case, the tumor showed diffuse CK7 and PAX8 positivity, along with HNF-1β positivity, and was negative for WT1. DNA mismatch repair (MMR) analysis revealed loss of nuclear expression of MSH2 and MSH6, while MLH1 and PMS2 remained intact, consistent with MMR deficiency. p53 staining showed a wild-type pattern. These findings collectively supported the diagnosis of gynecologic-type clear cell carcinoma of peritoneal origin. The identification of MMR deficiency carries important clinical implications. Loss of MSH2 and MSH6 expression raises the possibility of an underlying Lynch syndrome, warranting further genetic counseling and germline testing. Moreover, MMR deficiency has been associated with increased tumor mutational burden and may confer potential responsiveness to immune checkpoint inhibitors, even in malignancies such as clear cell carcinoma that are often considered chemoresistant. Recent molecular studies have provided insights into the genetic alterations associated with ovarian CCCs, with frequent mutations reported in ARID1A, PIK3CA, and KRAS (21). Peiró et al. (11) also described a pathogenic deletion in ARID1A and additional somatic mutations in GSDMB and KMT2C in a case of PPCCC. In our case, molecular analysis revealed ARID1A loss, consistent with the findings reported by Peiró et al. (11). In addition, NGS identified a PIK3CA H1047R mutation, expanding the molecular profile of PPCCC in this patient. PIK3CA, the catalytic subunit of PI3-kinase, is frequently mutated in a variety of cancers, including breast, endometrial, and cervical cancers. The H1047R mutation is known to be oncogenic. Preclinical data suggest that tumor harboring these PIK3CA mutations may be sensitive to isoform-selective PIK3CA inhibitors such as RLY-2608, highlighting a potential targeted therapy approach (22, 23). While data on PPCCC remain scarce, these overlapping molecular features suggest a potential shared pathogenesis with ovarian CCC, underscoring the importance of further molecular investigations to better characterize this rare malignancy. Moreover, the identification of potentially actionable mutations emphasizes the role of comprehensive molecular profiling in guiding future research and individualized therapeutic strategies (21, 24, 25). Clinically, PPCCC typically presents with abdominal pain, ascites, and a pelvic mass, as was observed in our patient (10). While the majority of reported cases remain confined to the peritoneal cavity, distant metastases beyond the peritoneal cavity has been documented in the skin and brain (9). In our case, metastatic involvement of the pancreas and spleen indicated advanced disease (FIGO stage IVB), highlighting the aggressive clinical behavior and poor prognosis often associated with PPCCC. Current treatment strategies for PPCCC are not well established due to its rarity and are generally extrapolated from protocols for epithelial ovarian carcinoma, including cytoreductive surgery followed by platinum-based chemotherapy. Despite such treatment, outcomes remain suboptimal, with frequent early recurrence and limited response to standard regimens. Immune checkpoint inhibitors targeting the PD-1/PD-L1 have been explored in CCC subtypes and have shown limited efficacy. Although our case was negative for PD-L1 expression, the presence of MMR deficiency may still provide a rationale for considering immunotherapy in the event of disease progression or recurrence. In conclusion, PPCCC is a rare and aggressive malignancy that poses significant diagnostic and therapeutic challenges. Accurate diagnosis requires thorough histologic, immunohistochemical, and clinical evaluation to exclude more common primary sites. This case contributes to the limited body of literature and highlights the need for further research into the pathogenesis, molecular characteristics, and potential targeted therapies for this underrecognized malignancy. Conclusion Primary peritoneal clear cell carcinoma (PPCCC) is an exceptionally rare malignancy, and its diagnosis remains challenging due to its rarity and overlapping features with more common tumors at this site. In many cases, it may be under-recognized or misclassified as metastatic disease from the ovary or other organs. Therefore, complete exclusion of other potential primary sites is essential. In addition to characteristic histopathological features, immunohistochemistry plays a critical role in the differential diagnosis, helping to distinguish PPCCC from ovarian, renal, and mesothelial neoplasms. Proper identification of this rare malignancy plays a crucial role in achieving a precise diagnosis and informing appropriate treatment strategies. Given the aggressive behavior and poor prognosis associated with PPCCC, further studies are needed to better understand its molecular pathogenesis and to establish optimized treatment protocols to reduce mortality. Abbreviations PPCCC Primary peritoneal clear cell carcinoma CCC Clear cell carcinoma CT Computed tomography MRI Magnetic resonance imaging H&E Hemotoxylin & eosion, MMR Mismatch repair DS debulking surgery LND lymph node dissection OM omentectomy CT chemotherapy RT radiotherapy NED no evidence of disease ROD recurrence of disease DOD dead of disease NA not available mo months. Declarations Acknowledgements The authors thank the staff of the Departments of Pathology at Chonnam National University Hospial for their support, and the patient for consenting to the publication of this case report. Author Contributions: N.I.K.: Original draft, supervision; J.S.L.: conceptualization and editing; K.H.L.: molecular testing and supervision; K.S.S.: writing—review and supervision. All authors have read and agreed to the published version of the manuscript. Funding The authors declare that they did not receive any funding for this work. Ethics approval and consent to participate The study was conducted in accordance with the Declaration of Helsinki and was approved by the Institutional Review Board of Chonnam National University Hospital (Gwangju, Korea) (approval number: CNUH-2025-365, approval date 04 November 2025). Consent for publication Written informed consent for publication of the patient’s clinical information and accompanying images was obtained from the patient. Availability of data and materials The dataset generated and analyzed during the current case report is available from the corresponding author upon reasonable request. Competing interests The authors declare that they have no competing interests. References Lee KR, Verma U, Belinson J. Primary clear cell carcinoma of the peritoneum. Gynecol Oncol. 1991;41(3):259–62. Johnson SB, Prisciandaro JI, Zhou J, Hadley SW, Reynolds RK, Jolly S. Primary peritoneal clear cell carcinoma treated with IMRT and interstitial HDR brachytherapy: a case report. 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Cite Share Download PDF Status: Published Journal Publication published 07 Feb, 2026 Read the published version in Journal of Ovarian Research → Version 1 posted Editorial decision: Revision requested 21 Jan, 2026 Reviews received at journal 20 Jan, 2026 Reviewers agreed at journal 11 Jan, 2026 Reviewers agreed at journal 29 Dec, 2025 Reviews received at journal 08 Dec, 2025 Reviewers agreed at journal 02 Dec, 2025 Reviewers invited by journal 02 Dec, 2025 Editor assigned by journal 02 Dec, 2025 Submission checks completed at journal 01 Dec, 2025 First submitted to journal 27 Nov, 2025 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. 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1","display":"","copyAsset":false,"role":"figure","size":113426,"visible":true,"origin":"","legend":"\u003cp\u003ePelvic MRI demonstrating a large mixed cystic and solid mass in pelvic cavity. (A) Sagittal view. (B) Coronal view showing heterogeneous enhancement and diffusion restriction within the solid component, suggestive of malignancy.\u003c/p\u003e","description":"","filename":"Slide1.jpg","url":"https://assets-eu.researchsquare.com/files/rs-8103498/v1/00d2430f17016d320e63642e.jpg"},{"id":97656555,"identity":"74f3ca0a-0ad1-4518-871b-ddc2c0f047ab","added_by":"auto","created_at":"2025-12-08 07:12:42","extension":"jpg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":95540,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eGross specimens of the resected tumors.\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e(A) Pancreas: Well-demarcated mass measuring approximately 2 cm, with solid and cystic components and hemorrhage.\u003cbr\u003e\n(B) Pelvic mass: Irregularly shaped solid mass with a lobulated and uneven surface\u003c/p\u003e\n\u003cp\u003e(C) Uterus and adnexa: Both ovaries and fallopian tubes appeared grossly unremarkable, except for a leiomyoma in the uterus; no primary tumor was identified.\u003c/p\u003e","description":"","filename":"Slide2.jpg","url":"https://assets-eu.researchsquare.com/files/rs-8103498/v1/6d4b9653381fdc50dbd656b6.jpg"},{"id":97674628,"identity":"68dd3d42-f21a-4dbf-ae25-5c675a36d573","added_by":"auto","created_at":"2025-12-08 09:43:44","extension":"jpg","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":386635,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eHistopathologic and immunohistochemical features of the peritoneal clear cell carcinoma.\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e(A) Low-power view showing a predominantly solid and papillary architecture with necrosis (H\u0026amp;E, ×20). (B) High-power view demonstrating tumor cells with round to oval nuclei, clear to eosinophilic cytoplasm and moderate nuclear atypia (H\u0026amp;E, ×100). (C,D) Tumor cells show diffuse positivity for PAX8 (C,×100) and HNF1β (D, ×100). (E,F) DNA mismatch repair analysis demonstrates retained MLH1 expression (E, ×100) but loss of MSH2 nuclear staining (F, ×100), indicating MMR deficiency.\u003c/p\u003e","description":"","filename":"Slide3.jpg","url":"https://assets-eu.researchsquare.com/files/rs-8103498/v1/048f78aebb67cec35f360b58.jpg"},{"id":102234172,"identity":"2df4be9c-bf61-43f6-b595-346200445895","added_by":"auto","created_at":"2026-02-09 16:07:08","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1236545,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-8103498/v1/c2dd07bb-2397-47c4-89e3-63c0f15000c1.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Primary peritoneal clear cell carcinoma with metastasis mimicking ovarian carcinoma: A case report and literature review","fulltext":[{"header":"Background","content":"\u003cp\u003ePrimary peritoneal clear cell carcinoma (PPCCC) is an exceptionally rare malignancy that closely resembles gynecologic epithelial cancers both clinically and histologically. While clear cell carcinoma (CCC) most commonly arises in the ovary or endometrium, its occurrence as a primary tumor in the peritoneum is exceedingly uncommon. Since its first description in 1990 (\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e), only a limited number of cases have been reported in the English literature (\u003cspan additionalcitationids=\"CR3 CR4 CR5 CR6 CR7 CR8 CR9 CR10 CR11 CR12 CR13 CR14\" citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e). Diagnosing PPCCC is challenging due to its overlapping morphological features with more common neoplasms originating from the ovary, endometrium and kidney. The pathogenesis of PPCCC remains poorly understood, though current hypotheses suggest possible origins from M\u0026uuml;llerian metaplasia or malignant transformation of endometriosis (\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e). However, many reported cases, including the present one, lack histological evidence of endometriosis or hormonal influence (\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e, \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e, \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e, \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e, \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e, \u003cspan additionalcitationids=\"CR14\" citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e). Given the rarity of reported cases, each new case provides valuable insights into the clinical and pathological spectrum of this underrecognized malignancy. Herein, we present a case of PPCCC in a 49-year-old woman without a history of endometriosis or hormone therapy, underscoring the diagnostic complexity and clinical significance of this unusual tumor.\u003c/p\u003e"},{"header":"Case presentation","content":"\u003cp\u003eA 48-year-old woman with no significant past medical or family history presented to a local clinic with acute lower abdominal pain. She had no prior history of hormone replacement therapy or endometriosis. Laboratory tests revealed elevated tumor markers, including CA 19-9 (777.3 U/mL) and CA 125 (242.9 U/mL), while CEA (1.3 ng/mL) and AFP (3.06 ng/mL) were within normal limits. Abdominal computed tomography (CT) revealed a 15\u0026times;10 mm oval-shaped, subtly enhancing lesion in the pancreatic tail, raising suspicion for either pancreatic adenocarcinoma or an islet cell tumor. Additionally, a 70\u0026times;65\u0026times;35 mm well-defined, heterogeneously enhancing solid mass was noted in the left pelvic cavity, suspicious for a malignant pelvic tumor or metastasis. The patient was referred to a tertiary care center for further evaluation. Upon transfer, pelvic magnetic resonance imaging (MRI) revealed an 11 cm mixed cystic and solid mass in the left adnexa, with the solid component demonstrating heterogeneous enhancement and diffusion restriction, suggestive of ovarian malignancy (Figure 1). Under the clinical impression of synchronous ovarian and pancreatic malignancies, the patient underwent total abdominal hysterectomy with bilateral salpingo-oophorectomy and distal pancreato-splenectomy. Intraoperatively, a large pelvic mass was identified within the pelvic peritoneum. Frozen section analysis performed during surgery initially suggested high-grade serous carcinoma of ovarian origin. A 2 cm encapsulated, well-demarcated mass was also identified in the pancreatic tail, adherent to the adjacent omentum, requiring adhesiolysis. However, both ovaries, fallopian tubes, and uterus appeared grossly unremarkable.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFigure 1.\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003ePelvic MRI demonstrating a large mixed cystic and solid mass in pelvic cavity. (A) Sagittal view. (B) Coronal view showing heterogeneous enhancement and diffusion restriction within the solid component, suggestive of malignancy.\u003c/p\u003e\n\u003cp\u003eGross pathological examination revealed a 12\u0026times;11\u0026times;3.5 cm pelvic mass with no apparent lesions in other gynecologic organs. The pancreatic tail contained a 3\u0026times;2.8\u0026times;2.5 cm cystic lesion with a friable whitish intraluminal mass. A 1.3\u0026times;1.1 cm cystic lesion was also observed in the spleen. Microscopically, the pancreatic, splenic, and pelvic masses shared identical histomorphological features, characterized by solid and papillary architecture with focal necrosis. Tumor cells displayed round to oval nuclei with irregular contours, clear to eosinophilic cytoplasm, and moderate nuclear atypia. Mitotic activity was variable, and occasional eosinophilic hyaline globules were noted (Figure 2). No lymphovascular or perineural invasion was noted. The specimens also lacked any histologic features suggestive of endometriosis, such as endometrial glands, stroma, or hemosiderin-laden macrophages. Immunohistochemical staining showed positivity for PAX8, CK7, and HNF1\u0026beta;, and negativity for CK20, p16, WT1, and calretinin. p53 staining revealed a wild-type expression pattern.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eDNA mismatch repair (MMR) immunostaining demonstrated loss of nuclear expression of MSH2 and MSH6, while MLH1 and PMS2 remained intact, indicating MMR deficiency (Figure 3). To exclude a gynecologic origin of the clear cell carcinoma, the ovaries, fallopian tubes, and uterus were serially and thoroughly sectioned for microscopic examination. However, no evidence of a primary tumor was identified. Next generation sequencing (NGS) of the tumor revealed loss of ARID1A, along with additional somatic mutations in PIK3CA H1047R and PIK3CA Q546L.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eDiscussion\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFigure 2. Gross specimens of the resected tumors.\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e(A) Pancreas: Well-demarcated mass measuring approximately 2 cm, with solid and cystic components and hemorrhage.\u003cbr\u003e\u0026nbsp;(B) Pelvic mass: Irregularly shaped solid mass with a lobulated and uneven surface\u003c/p\u003e\n\u003cp\u003e(C) Uterus and adnexa: Both ovaries and fallopian tubes appeared grossly unremarkable, except for a leiomyoma in the uterus; no primary tumor was identified.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFigure 3. Histopathologic and immunohistochemical features of the peritoneal clear cell carcinoma.\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e(A) Low-power view showing a predominantly solid and papillary architecture with necrosis (H\u0026amp;E, \u0026times;20). (B) High-power view demonstrating tumor cells with round to oval nuclei, clear to eosinophilic cytoplasm and moderate nuclear atypia (H\u0026amp;E, \u0026times;100). (C,D) Tumor cells show diffuse positivity for PAX8 (C,\u0026times;100) and HNF1\u0026beta; (D, \u0026times;100). (E,F) DNA mismatch repair analysis demonstrates retained MLH1 expression (E, \u0026times;100) but loss of MSH2 nuclear staining (F, \u0026times;100), indicating MMR deficiency.\u003c/p\u003e\n\u003cp\u003eBased on intraoperative findings, histopathological features, immunohistochemical profile and molecular characteristics by NGS, the final diagnosis was primary peritoneal clear cell carcinoma, with metastases to the pancreas and spleen, a highly unusual presentation. The patient was diagnosed with stage IVB primary peritoneal clear cell carcinoma, and the case was discussed at a multidisciplinary tumor board to determine the appropriate adjuvant treatment. The patient is scheduled to undergo six cycles of chemotherapy with gemcitabine and carboplatin.\u003c/p\u003e"},{"header":"Discussion","content":"\u003cp\u003ePrimary peritoneal carcinoma (PPC) is a rare epithelial malignancy that arises from the peritoneal lining, with diagnostic criteria established by the Gynecologic Oncology Group (GOG) (16). According to these criteria, PPC can be diagnosed when both ovaries are either normal in size or only benignly enlarged, and when the extent of peritoneal involvement exceeds that of the ovarian surface. Primary peritoneal clear cell carcinoma (PPCCC) represents an exceedingly rare histologic subtype of PPC, accounting for approximately 3% of cases (17). Histologically, it is indistinguishable from clear cell carcinomas (CCCs) of M\u0026uuml;llerian origin, particularly those of the ovary and endometrium. Therefore, meticulous exclusion of other primary sites is essential for establishing a diagnosis. In the present case, serial sectioning and detailed histopathologic evaluation of the uterus, ovaries, and fallopian tubes revealed no evidence of a primary tumor, thereby fulfilling the GOG criteria for PPC and supporting a diagnosis of PPCCC.\u003c/p\u003e\n\u003cp\u003eWhile the pathogenesis of PPCCC remains poorly understood, the most widely accepted hypotheses suggest either M\u0026uuml;llerian metaplasia or malignant transformation of endometriosis (11). However, extraovarian malignant transformation of endometriosis is extremely rare, occurring in only 1.6% of cases (18). In previous reports, approximately one-third of patients with PPCCC had a history of endometriosis, and endometriotic foci were often found histologically (10, 17). In our case, however, extensive histologic sampling failed to demonstrate any features of endometriosis, such as endometrial-type glands or stroma, or hemosiderin-laden macrophages.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eA review of previously reported PPCCC cases is summarized in Table 1, providing an overview of \u003cstrong\u003e\u003cbr\u003e\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTable 1. Literature review for cases of clear cell carcinoma of peritoneum\u003c/strong\u003e\u003c/p\u003e\n\u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eAuthors\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eAge\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eTumor location\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eEndometriosis\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eTreatment\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eOutcome\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eMolecular characteristics\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eEvans et al. (26)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e54\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eSigmoid mesocolon\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eYes\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eDS + RT\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eNA\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eNA\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eLee et al. (1)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e67\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003ePelvic cavity\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eNo\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eDS + TAHBSO\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eNA\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eNA\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eTziortzioti et al. (7)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e62\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003ePeritoneum and omentum\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eNo\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eDS + TAHBSO + OM + CT\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eDOD at 6 mo\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eNA\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eIchimura et al. (6)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e45\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003ePelvic cavity\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eYes\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eDS + TAHBSO + CT\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eROD at 32 mo\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eNA\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eHama et al. (5)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e53\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003ePeritoneum\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eYes\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eDS + BSO + CT\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eDOD at 5 mo\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eNA\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eTerada et al. (13)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e49\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eGastric peritoneal, splenic hilus\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eNo\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eDS\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eNED at 6 mo\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eNA\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eTakano et al. (14)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e53\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eUpper abdomen and omentum\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eNo\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eDS + CT\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eDOD at 5 mo\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eNA\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eTakano et al. (14)\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e66\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eOmentum and peritoneum\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eNo\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eDS + TAHBSO + OM + LND + CT\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eNED at 20 mo\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eNA\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eMatsuo et al. (4)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e37\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eAbdominal scar\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eYes\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eDS + CT\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eROD at 18 mo\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eNA\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eMuezzinoglu et al. (3)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e54\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eAbdomen\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eYes\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eDS + TAHBSO + CT\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eNED at 12 mo\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eNA\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eJohnson et al. (2)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e54\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eProximal vagina and vaginal cuff\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eNo\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eCT + RT\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eROD at 4 mo\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eNA\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eShigeta et al. (10)\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e59\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eDouglas pouch\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eYes\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eDS + TAHBSO + LND + CT\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eNED at 5 mo\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eNA\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003ePeiro et al. (11)\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e48\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003ePeritoneum\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eNo\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eTAHBSO + OM + CT\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eNED at 28 mo\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eARID1A loss\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eGiannakopoulos et al. (15)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e61\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003ePeritoneum\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eNo\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eDS\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eNED at 2 mo\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eAlves et al. (9)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e34\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003ePeritoneum\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eNo\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eTAH + LND + OM + CT\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eDOD at 24 mo\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eBRCA1A unknown significance\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003ePresent case\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e48\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003ePelvic peritoneum\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eNo\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eTAHBSO + CT\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eNED at 1 mo\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eARID1A loss\u003c/p\u003e\n \u003cp\u003ePIK3CA H1047R\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003epatient demographics, tumor location, history of endometriosis, molecular findings and clinical outcomes. Most cases involved women in their 40s to 60s, with endometriosis present in only a subset of cases, reflecting the heterogeneous pathogenesis of this malignancy. Our case shares similar histopathologic features but is distinguished by DNA mismatch repair deficiency and ARID1A loss on NGS, highlighting both overlapping and unique molecular characteristics. The differential diagnosis of CCC arising in the peritoneum includes high-grade serous carcinoma, malignant mesothelioma, and metastatic clear cell carcinomas from other organs, particularly the kidney. High-grade serous carcinoma is characterized by marked nuclear atypia, frequent mitotic figures, and a complex papillary or solid architecture (19). In contrast, malignant mesothelioma often demonstrates relatively bland cytologic features and simple papillary formations lined by a single layer of uniform mesothelial cells. Despite morphologic overlap with CCC, these entities can usually be distinguished through a combination of histologic evaluation and imunohistochemical profiling. Among metastatic tumors, clear cell renal cell carcinoma (CCRCC), is an important consideration. CCRCC typically displays a nested-alveolar growth pattern with rich stromal vasculature, whereas M\u0026uuml;llerian-type CCC is characterized by tubulocystic architecture, small rounded papillae, and hobnail cells (20). Immunohistochemically, CCRCC is frequently negative for CK7, HNF1 beta, whereas CCCs of gynecologic origin are typically positive for these markers. In our case, the tumor showed diffuse CK7 and PAX8 positivity, along with HNF-1\u0026beta; positivity, and was negative for WT1. DNA mismatch repair (MMR) analysis revealed loss of nuclear expression of MSH2 and MSH6, while MLH1 and PMS2 remained intact, consistent with MMR deficiency. p53 staining showed a wild-type pattern. These findings collectively supported the diagnosis of gynecologic-type clear cell carcinoma of peritoneal origin.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe identification of MMR deficiency carries important clinical implications. Loss of MSH2 and MSH6 expression raises the possibility of an underlying Lynch syndrome, warranting further genetic counseling and germline testing. Moreover, MMR deficiency has been associated with increased tumor mutational burden and may confer potential responsiveness to immune checkpoint inhibitors, even in malignancies such as clear cell carcinoma that are often considered chemoresistant.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eRecent molecular studies have provided insights into the genetic alterations associated with ovarian CCCs, with frequent mutations reported in ARID1A, PIK3CA, and KRAS (21). Peir\u0026oacute; et al. (11) also described a pathogenic deletion in ARID1A and additional somatic mutations in GSDMB and KMT2C in a case of PPCCC. In our case, molecular analysis revealed ARID1A loss, consistent with the findings reported by Peir\u0026oacute; et al. (11). In addition, NGS identified a PIK3CA H1047R mutation, expanding the molecular profile of PPCCC in this patient. PIK3CA, the catalytic subunit of PI3-kinase, is frequently mutated in a variety of cancers, including breast, endometrial, and cervical cancers. The H1047R mutation is known to be oncogenic. Preclinical data suggest that tumor harboring these PIK3CA mutations may be sensitive to isoform-selective PIK3CA inhibitors such as RLY-2608, highlighting a potential targeted therapy approach (22, 23). While data on PPCCC remain scarce, these overlapping molecular features suggest a potential shared pathogenesis with ovarian CCC, underscoring the importance of further molecular investigations to better characterize this rare malignancy. Moreover, the identification of potentially actionable mutations emphasizes the role of comprehensive molecular profiling in guiding future research and individualized therapeutic strategies (21, 24, 25).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eClinically, PPCCC typically presents with abdominal pain, ascites, and a pelvic mass, as was observed in our patient (10). While the majority of reported cases remain confined to the peritoneal cavity, distant metastases beyond the peritoneal cavity has been documented in the skin and brain (9). In our case, metastatic involvement of the pancreas and spleen indicated advanced disease (FIGO stage IVB), highlighting the aggressive clinical behavior and poor prognosis often associated with PPCCC. \u0026nbsp;Current treatment strategies for PPCCC are not well established due to its rarity and are generally extrapolated from protocols for epithelial ovarian carcinoma, including cytoreductive surgery followed by platinum-based chemotherapy. Despite such treatment, outcomes remain suboptimal, with frequent early recurrence and limited response to standard regimens. Immune checkpoint inhibitors targeting the PD-1/PD-L1 have been explored in CCC subtypes and have shown limited efficacy. Although our case was negative for PD-L1 expression, the presence of MMR deficiency may still provide a rationale for considering immunotherapy in the event of disease progression or recurrence.\u003c/p\u003e\n\u003cp\u003eIn conclusion, PPCCC is a rare and aggressive malignancy that poses significant diagnostic and therapeutic challenges. Accurate diagnosis requires thorough histologic, immunohistochemical, and clinical evaluation to exclude more common primary sites. This case contributes to the limited body of literature and highlights the need for further research into the pathogenesis, molecular characteristics, and potential targeted therapies for this underrecognized malignancy.\u0026nbsp;\u003c/p\u003e"},{"header":"Conclusion","content":"\u003cp\u003ePrimary peritoneal clear cell carcinoma (PPCCC) is an exceptionally rare malignancy, and its diagnosis remains challenging due to its rarity and overlapping features with more common tumors at this site. In many cases, it may be under-recognized or misclassified as metastatic disease from the ovary or other organs. Therefore, complete exclusion of other potential primary sites is essential. In addition to characteristic histopathological features, immunohistochemistry plays a critical role in the differential diagnosis, helping to distinguish PPCCC from ovarian, renal, and mesothelial neoplasms. Proper identification of this rare malignancy plays a crucial role in achieving a precise diagnosis and informing appropriate treatment strategies. Given the aggressive behavior and poor prognosis associated with PPCCC, further studies are needed to better understand its molecular pathogenesis and to establish optimized treatment protocols to reduce mortality.\u003c/p\u003e"},{"header":"Abbreviations","content":"\u003cdiv class=\"DefinitionList\"\u003e\u003cdiv class=\"DefinitionListEntry\"\u003e\u003cdiv class=\"Term\"\u003ePPCCC\u003c/div\u003e\u003cdiv class=\"Description\"\u003e\u003cp\u003ePrimary peritoneal clear cell carcinoma\u003c/p\u003e\u003c/div\u003e\u003c/div\u003e\u003cdiv class=\"DefinitionListEntry\"\u003e\u003cdiv class=\"Term\"\u003eCCC\u003c/div\u003e\u003cdiv class=\"Description\"\u003e\u003cp\u003eClear cell carcinoma\u003c/p\u003e\u003c/div\u003e\u003c/div\u003e\u003cdiv class=\"DefinitionListEntry\"\u003e\u003cdiv class=\"Term\"\u003eCT\u003c/div\u003e\u003cdiv class=\"Description\"\u003e\u003cp\u003eComputed tomography\u003c/p\u003e\u003c/div\u003e\u003c/div\u003e\u003cdiv class=\"DefinitionListEntry\"\u003e\u003cdiv class=\"Term\"\u003eMRI\u003c/div\u003e\u003cdiv class=\"Description\"\u003e\u003cp\u003eMagnetic resonance imaging\u003c/p\u003e\u003c/div\u003e\u003c/div\u003e\u003cdiv class=\"DefinitionListEntry\"\u003e\u003cdiv class=\"Term\"\u003eH\u0026amp;E\u003c/div\u003e\u003cdiv class=\"Description\"\u003e\u003c/div\u003e\u003c/div\u003e\u003cdiv class=\"DefinitionListEntry\"\u003e\u003cdiv class=\"Term\"\u003eHemotoxylin \u0026amp; eosion, MMR\u003c/div\u003e\u003cdiv class=\"Description\"\u003e\u003cp\u003eMismatch repair\u003c/p\u003e\u003c/div\u003e\u003c/div\u003e\u003cdiv class=\"DefinitionListEntry\"\u003e\u003cdiv class=\"Term\"\u003eDS\u003c/div\u003e\u003cdiv class=\"Description\"\u003e\u003cp\u003edebulking surgery\u003c/p\u003e\u003c/div\u003e\u003c/div\u003e\u003cdiv class=\"DefinitionListEntry\"\u003e\u003cdiv class=\"Term\"\u003eLND\u003c/div\u003e\u003cdiv class=\"Description\"\u003e\u003cp\u003elymph node dissection\u003c/p\u003e\u003c/div\u003e\u003c/div\u003e\u003cdiv class=\"DefinitionListEntry\"\u003e\u003cdiv class=\"Term\"\u003eOM\u003c/div\u003e\u003cdiv class=\"Description\"\u003e\u003cp\u003eomentectomy\u003c/p\u003e\u003c/div\u003e\u003c/div\u003e\u003cdiv class=\"DefinitionListEntry\"\u003e\u003cdiv class=\"Term\"\u003eCT\u003c/div\u003e\u003cdiv class=\"Description\"\u003e\u003cp\u003echemotherapy\u003c/p\u003e\u003c/div\u003e\u003c/div\u003e\u003cdiv class=\"DefinitionListEntry\"\u003e\u003cdiv class=\"Term\"\u003eRT\u003c/div\u003e\u003cdiv class=\"Description\"\u003e\u003cp\u003eradiotherapy\u003c/p\u003e\u003c/div\u003e\u003c/div\u003e\u003cdiv class=\"DefinitionListEntry\"\u003e\u003cdiv class=\"Term\"\u003eNED\u003c/div\u003e\u003cdiv class=\"Description\"\u003e\u003cp\u003eno evidence of disease\u003c/p\u003e\u003c/div\u003e\u003c/div\u003e\u003cdiv class=\"DefinitionListEntry\"\u003e\u003cdiv class=\"Term\"\u003eROD\u003c/div\u003e\u003cdiv class=\"Description\"\u003e\u003cp\u003erecurrence of disease\u003c/p\u003e\u003c/div\u003e\u003c/div\u003e\u003cdiv class=\"DefinitionListEntry\"\u003e\u003cdiv class=\"Term\"\u003eDOD\u003c/div\u003e\u003cdiv class=\"Description\"\u003e\u003cp\u003edead of disease\u003c/p\u003e\u003c/div\u003e\u003c/div\u003e\u003cdiv class=\"DefinitionListEntry\"\u003e\u003cdiv class=\"Term\"\u003eNA\u003c/div\u003e\u003cdiv class=\"Description\"\u003e\u003cp\u003enot available\u003c/p\u003e\u003c/div\u003e\u003c/div\u003e\u003cdiv class=\"DefinitionListEntry\"\u003e\u003cdiv class=\"Term\"\u003emo\u003c/div\u003e\u003cdiv class=\"Description\"\u003e\u003cp\u003emonths.\u003c/p\u003e\u003c/div\u003e\u003c/div\u003e\u003c/div\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAcknowledgements\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors thank the staff of the Departments of Pathology at Chonnam National University Hospial for their support, and the patient for consenting to the publication of this case report.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor Contributions:\u003c/strong\u003e N.I.K.: Original draft, supervision; J.S.L.: conceptualization and editing; K.H.L.: molecular testing and supervision; K.S.S.: writing\u0026mdash;review and supervision. All authors have read and agreed to the published version of the manuscript.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare that they did not receive any funding for this work.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eEthics approval and consent to participate\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe study was conducted in accordance with the Declaration of Helsinki and was approved by the Institutional Review Board of Chonnam National University Hospital (Gwangju, Korea) (approval number: CNUH-2025-365, approval date 04 November 2025).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConsent for publication\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eWritten informed consent for publication of the patient\u0026rsquo;s clinical information and accompanying images was obtained from the patient.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAvailability of data and materials\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe dataset generated and analyzed during the current case report is available from the corresponding author upon reasonable request.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCompeting interests\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare that they have no competing interests.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eLee KR, Verma U, Belinson J. Primary clear cell carcinoma of the peritoneum. Gynecol Oncol. 1991;41(3):259\u0026ndash;62.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eJohnson SB, Prisciandaro JI, Zhou J, Hadley SW, Reynolds RK, Jolly S. Primary peritoneal clear cell carcinoma treated with IMRT and interstitial HDR brachytherapy: a case report. J Appl Clin Med Phys. 2014;15(1):4520.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eMuezzinoglu B, Corak S, Yucesoy I. Primary peritoneal clear cell adenocarcinoma associated with endometriosis. Appl Immunohistochem Mol Morphol. 2011;19(4):384\u0026ndash;5.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eMatsuo K, Alonsozana EL, Eno ML, Rosenshein NB, Im DD. Primary peritoneal clear cell adenocarcinoma arising in previous abdominal scar for endometriosis surgery. Arch Gynecol Obstet. 2009;280(4):637\u0026ndash;41.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eHama Y, Iwasaki Y, Sakata I, Kusano S. Primary peritoneal clear cell carcinoma. J Comput Assist Tomogr. 2004;28(5):617\u0026ndash;9.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eIchimura T, Ishiko O, Nishimura S, Kojima T, Shimura K. Primary peritoneal clear cell carcinoma: excellent results from paclitaxel and carboplatin combination chemotherapy. Oncol Rep. 2001;8(6):1243\u0026ndash;5.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eTziortzioti V, Apessou D, Antoniou S, Giantzoglou A, Paissios P. Clear cell adenocarcinoma of the peritoneum associated with clear cell adenocarcinoma arising in an endometrial polyp. J Obstet Gynaecol. 1999;19(5):557\u0026ndash;8.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eZhang CJ, Sun GP, Liu H, Peng WR, Xiong FX, Pan YY, et al. Primary clear cell adenocarcinoma of the peritoneum presents as Sister Mary Joseph's nodule: a case report and literature review. Eur J Gynaecol Oncol. 2014;35(6):745\u0026ndash;8.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eAlves FR, Malheiro M, Ferreira A, Miranda H, Martins A. Cutaneous and Cerebral Metastases From Primary Peritoneal Clear Cell Carcinoma. Cureus. 2022;14(1):e21282.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eShigeta N, Yoshino K, Matsuzaki S, Morii E, Ueda Y, Kimura T. Clear cell adenocarcinoma of the peritoneum: a case report and literature review. J Ovarian Res. 2014;7:86.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003ePeiro G, Silva-Ortega S, Garcia-Espasa C, Sala-Ferichola M, Perez-Vicente S, Castellon-Molla E, et al. Primary peritoneal clear cell carcinoma. A case report and literature review. Gynecol Oncol Rep. 2020;32:100551.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eHarris CM, Singleton MP, Samulski T, Clark LH. Primary peritoneal clear cell carcinoma arising in the setting of abdominal wall Endometriosis: A case report and review of the literature. Gynecol Oncol Rep. 2024;53:101370.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eTerada T, Kawaguchi M. Primary clear cell adenocarcinoma of the peritoneum. Tohoku J Exp Med. 2005;206(3):271\u0026ndash;5.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eTakano M, Yoshikawa T, Kato M, Aida S, Goto T, Furuya K, et al. Primary clear cell carcinoma of the peritoneum: report of two cases and a review of the literature. Eur J Gynaecol Oncol. 2009;30(5):575\u0026ndash;8.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eGiannakopoulos N, Henning L, Svensson \u0026Aring;, De La Parra JJB, Ranhem C. Primary peritoneal clear cell carcinoma. Int J Gynecol Cancer. 2022;32(9):1201\u0026ndash;4.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eAyhan A, Gultekin M, Dursun P, editors. Textbook of Gynaecological Oncology. Golden ed. Ankara: Gunes Publishing; 2017.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eInsabato L, Natella V, Somma A, Persico M, Camera L, Losito NS, et al. Primary peritoneal clear cell carcinoma versus ovarian carcinoma versus malignant transformation of endometriosis: a vexing issue. Int J Surg Pathol. 2015;23(3):211\u0026ndash;6.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eThomas EJ, Campbell IG. Evidence that endometriosis behaves in a malignant manner. Gynecol Obstet Invest. 2000;50(Suppl 1):2\u0026ndash;10.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eTaylor H, Costigan D. Ovarian clear cell carcinoma: an overview of key histopathologic features. Int J Gynecol Cancer. 2023;33(5):843\u0026ndash;4.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eJi JX, Wang YK, Cochrane DR, Huntsman DG. Clear cell carcinomas of the ovary and kidney: clarity through genomics. J Pathol. 2018;244(5):550\u0026ndash;64.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eKim SI, Lee JW, Lee M, Kim HS, Chung HH, Kim JW, et al. Genomic landscape of ovarian clear cell carcinoma via whole exome sequencing. Gynecol Oncol. 2018;148(2):375\u0026ndash;82.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eVarkaris A, Pazolli E, Gunaydin H, Wang Q, Pierce L, Boezio AA, et al. Discovery and Clinical Proof-of-Concept of RLY-2608, a First-in-Class Mutant-Selective Allosteric PI3Kα Inhibitor That Decouples Antitumor Activity from Hyperinsulinemia. Cancer Discov. 2024;14(2):240\u0026ndash;57.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eLi H, Wen X, Ren Y, Fan Z, Zhang J, He G, et al. Targeting PI3K family with small-molecule inhibitors in cancer therapy: current clinical status and future directions. Mol Cancer. 2024;23(1):164.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eXie Y, Kong W, Luo D, Chen S, Zhao X, Zhang HE. Ovarian Clear Cell Carcinoma: Genomic Characterization, Pathogenesis and Targeted Therapy. Anticancer Res. 2023;43(8):3401\u0026ndash;10.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eStewart J, Cunningham N, Banerjee S. New therapies for clear cell ovarian carcinoma. Int J Gynecol Cancer. 2023;33(3):385\u0026ndash;93.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eEvans H, Yates WA, Palmer WE, Cartwright RL, Antemann RW. Clear cell carcinoma of the sigmoid mesocolon: a tumor of the secondary m\u0026uuml;llerian system. Am J Obstet Gynecol. 1990;162(1):161\u0026ndash;3.\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"journal-of-ovarian-research","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"jovr","sideBox":"Learn more about [Journal of Ovarian Research](http://ovarianresearch.biomedcentral.com)","snPcode":"13048","submissionUrl":"https://submission.nature.com/new-submission/13048/3","title":"Journal of Ovarian Research","twitterHandle":"@BioMedCentral","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"BMC/SO AJ","inReviewEnabled":true,"inReviewRevisionsEnabled":true},"keywords":"Primary peritoneum carcinoma, Clear cell carcinoma, Endometriosis","lastPublishedDoi":"10.21203/rs.3.rs-8103498/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-8103498/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003ch2\u003eBackground\u003c/h2\u003e\u003cp\u003ePrimary peritoneal clear cell carcinoma (PPCCC) is an exceptionally rare malignancy that closely resembles gynecologic epithelial cancers clinically and histologically. Its pathogenesis is poorly understood, with possible origins from M\u0026uuml;llerian metaplasia or malignant transformation of endometriosis.\u003c/p\u003e\u003ch2\u003eCase presentation\u003c/h2\u003e\u003cp\u003eA 48-year-old woman with no history of endometriosis or hormone therapy presented with acute lower abdominal pain. Imaging revealed a pelvic mass and a lesion in the pancreatic tail. The patient underwent hysterectomy with bilateral salpingo-oophorectomy and distal pancreatectomy with splenectomy. Intraoperatively, the pelvic mass was located in the peritoneum, while the gynecologic organs appeared grossly normal. Histopathologic examination of the pelvic, pancreatic, and splenic lesions revealed identical features of clear cell carcinoma. Immunohistochemistry demonstrated positivity for PAX8, CK7, and HNF1β, with loss of MSH2 and MSH6. Next-generation sequencing revealed ARID1A loss and somatic PIK3CA mutations. No primary ovarian, endometrial, or renal tumor was detected, supporting a diagnosis of primary peritoneal clear cell carcinoma with metastases to the pancreas and spleen.\u003c/p\u003e\u003ch2\u003eConclusions\u003c/h2\u003e\u003cp\u003eThis case highlights the diagnostic challenges of PPCCC and offers valuable insights into the clinical and pathological spectrum of this underrecognized malignancy.\u003c/p\u003e","manuscriptTitle":"Primary peritoneal clear cell carcinoma with metastasis mimicking ovarian carcinoma: A case report and literature review","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-12-08 07:12:37","doi":"10.21203/rs.3.rs-8103498/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2026-01-21T12:39:35+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2026-01-20T15:20:22+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"146381304809546192037059605349954709158","date":"2026-01-12T01:11:13+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"136155908742860681705155105228632515946","date":"2025-12-30T03:17:15+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-12-09T03:14:50+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"169165856541867998684050752514174662356","date":"2025-12-03T04:46:36+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2025-12-03T03:45:12+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2025-12-02T06:09:09+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2025-12-01T12:57:04+00:00","index":"","fulltext":""},{"type":"submitted","content":"Journal of Ovarian Research","date":"2025-11-27T08:49:15+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"journal-of-ovarian-research","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"jovr","sideBox":"Learn more about [Journal of Ovarian Research](http://ovarianresearch.biomedcentral.com)","snPcode":"13048","submissionUrl":"https://submission.nature.com/new-submission/13048/3","title":"Journal of Ovarian Research","twitterHandle":"@BioMedCentral","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"BMC/SO AJ","inReviewEnabled":true,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"eb7f65e9-4aca-48cc-baac-266ed9a7425b","owner":[],"postedDate":"December 8th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2026-02-09T16:04:18+00:00","versionOfRecord":{"articleIdentity":"rs-8103498","link":"https://doi.org/10.1186/s13048-026-02009-w","journal":{"identity":"journal-of-ovarian-research","isVorOnly":false,"title":"Journal of Ovarian Research"},"publishedOn":"2026-02-07 15:57:04","publishedOnDateReadable":"February 7th, 2026"},"versionCreatedAt":"2025-12-08 07:12:37","video":"","vorDoi":"10.1186/s13048-026-02009-w","vorDoiUrl":"https://doi.org/10.1186/s13048-026-02009-w","workflowStages":[]},"version":"v1","identity":"rs-8103498","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-8103498","identity":"rs-8103498","version":["v1"]},"buildId":"k6vKHA0u1VdKjwwnw531e","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}