Abdominal wall clear cell carcinoma arising on cesarean-scar endometriosis: a case report

A 48-year-old woman (gravida 1, para 1) was referred for evaluation of a progressively enlarging lower abdominal wall mass. She had undergone one lower-segment cesarean section approximately 20 years earlier and subsequently developed a condition that was clinically and radiologically diagnosed as cesarean scar endometriosis. She had no significant past medical history, no history of malignancy, no known drug allergies, and was not receiving any long-term medications. There was no reported family history of gynecologic or gastrointestinal malignancy, and she denied tobacco or alcohol use. Over time, the lesion enlarged and became firmer and more infiltrative. 1 year before referral, she was hospitalized with fever and chills. Examination showed a firm, poorly defined mass involving the left side of the cesarean scar. Ultrasonography revealed a 47 × 58 × 64 mm heterogeneous, hypoechoic subcutaneous mass with irregular margins. Laboratory evaluation showed elevated inflammatory markers and liver enzymes (ESR 125 mm/h, SGOT 146 U/L, SGPT 210 U/L, CRP 207 mg/L). Contrast-enhanced CT demonstrated a 60 × 56 × 45 mm solid mass deep to the rectus sheath and a 40 × 22 mm enlarged, enhancing left external iliac lymph node, raising concern for malignant transformation of AWE. Months later, the mass enlarged further and was accompanied by weight loss, a persistent nonproductive cough, and liver enzyme elevation. Pelvic MRI revealed a 6-cm infiltrative, enhancing mass involving the left rectus abdominis with adjacent hemorrhagic cystic foci, a necrotic left external iliac nodal mass, and a separate 4-cm left pelvic lesion with peripheral enhancement and central necrosis (Fig. 1 A–E). Serum CA-125 and CA 19-9 were elevated to 228 and 90 U/mL, respectively. Figure 1. (A–E) Pretreatment MRI: Axial images demonstrate two distinct masses. Images A (T2-weighted), B (contrast-enhanced), and C (DWI) show a subcutaneous abdominal wall mass involving the left rectus abdominis muscle (blue arrow in Image A). This mass exhibits intermediate signal intensity on T2, heterogeneous enhancement, and restricted diffusion. Images D (axial T2-weighted) and E (axial post-contrast) reveal a second mass in the left external iliac chain, characterized by heterogeneous enhancement and central necrosis (blue arrow in Image D). (A–E) Pretreatment MRI: Axial images demonstrate two distinct masses. Images A (T2-weighted), B (contrast-enhanced), and C (DWI) show a subcutaneous abdominal wall mass involving the left rectus abdominis muscle (blue arrow in Image A). This mass exhibits intermediate signal intensity on T2, heterogeneous enhancement, and restricted diffusion. Images D (axial T2-weighted) and E (axial post-contrast) reveal a second mass in the left external iliac chain, characterized by heterogeneous enhancement and central necrosis (blue arrow in Image D). The differential diagnosis included malignant transformation of AWE, soft tissue sarcoma, metastatic carcinoma, desmoid-type fibromatosis, and a primary gynecologic malignancy with abdominal wall extension. Image-guided core needle biopsy was interpreted as metastatic serous carcinoma, most likely of ovarian origin. Following a multidisciplinary tumor board discussion, she received three cycles of neoadjuvant carboplatin and paclitaxel, with a partial radiologic response. She then underwent exploratory laparotomy, encompassing en bloc abdominal wall resection with negative margins, total abdominal hysterectomy, bilateral salpingo-oophorectomy, bilateral pelvic lymphadenectomy, infracolic omentectomy, and excision of the enlarged obturator lymph node. Complete macroscopic cytoreduction was achieved. Final pathology revealed CCC arising from AWE, with benign endometrial-type glands adjacent to invasive carcinoma, fulfilling accepted criteria for malignant transformation of endometriosis. The tumor showed papillary, tubulocystic, and solid architectural patterns (Fig. 2 A–E). One left inguinal lymph node contained metastatic carcinoma; all gynecologic organs and remaining lymph nodes were negative, confirming a primary abdominal wall origin. Postoperative MRI showed no residual mass (Fig. 3 A,B). She completed adjuvant carboplatin and paclitaxel followed by maintenance bevacizumab. At 2 years, she remained alive without clinical or radiologic recurrence and continued regular surveillance. The clinical course is summarized in Table 1 . Figure 2. Histopathologic features of abdominal wall clear cell carcinoma arising in scar endometriosis (H&E stain). A. (H&E × 40) View of the abdominal wall lesion showing an infiltrative epithelial neoplasm expanding fibromuscular and fibroadipose tissue, adjacent to thick-walled vessels and fibrotic stroma. The overall appearance is consistent with a deeply infiltrative Müllerian-type carcinoma involving the abdominal wall. B. (H&E × 100) Area of abdominal wall endometriosis composed of benign endometrial-type glands embedded in fibrous stroma with an associated chronic inflammatory infiltrate, in close proximity to the invasive carcinoma. This relationship supports malignant transformation of pre-existing abdominal wall endometriosis according to the Sampson and Scott criteria. C. (H&E × 100) View demonstrating complex papillary and tubulocystic architecture lined by atypical epithelial cells with clear to eosinophilic cytoplasm and enlarged nuclei, typical of clear cell carcinoma arising in an endometriosis-associated abdominal wall lesion. D. (H&E × 400) View highlighting tubulocystic and papillary structures lined by a single layer of cuboidal to hobnail tumor cells with clear cytoplasm and conspicuous nuclear atypia. These features are characteristic of Müllerian-type clear cell carcinoma. E. (H&E × 200) View of solid-predominant areas of the abdominal wall clear cell carcinoma composed of sheets and nests of polygonal cells with abundant clear to finely granular cytoplasm and pleomorphic nuclei. The combination of papillary, tubulocystic, and solid patterns is typical of clear cell carcinoma associated with endometriosis. Figure 3. (A, B) Post-treatment pelvic MRI images. Image A (axial T2-weighted) and image B (sagittal T2-weighted) demonstrate findings consistent with previous surgery, including removal of the abdominal wall mass and total abdominal hysterectomy with bilateral salpingo-oophorectomy. A fluid collection is noted at the surgical site, consistent with postoperative change. Table 1 Clinical timeline of diagnosis and treatment. Time Clinical event ~20 years before presentation Cesarean section Following years Development of cesarean scar endometriosis 1 year before referral Fever and chills; abdominal wall mass identified on ultrasound Same admission CT demonstrated abdominal wall mass and enlarged external iliac lymph node Following months Progressive enlargement, weight loss, cough Preoperative work-up MRI, tumor markers, and core biopsy performed Diagnosis Core biopsy favored metastatic serous carcinoma Neoadjuvant treatment Three cycles of carboplatin–paclitaxel Surgery Complete cytoreductive surgery with abdominal wall resection, hysterectomy, bilateral salpingo-oophorectomy, lymphadenectomy, and omentectomy Final pathology Clear cell carcinoma arising in abdominal wall endometriosis Postoperative management Adjuvant chemotherapy and maintenance bevacizumab Follow-up No residual disease on MRI; ongoing surveillance for 2 years Histopathologic features of abdominal wall clear cell carcinoma arising in scar endometriosis (H&E stain). A. (H&E × 40) View of the abdominal wall lesion showing an infiltrative epithelial neoplasm expanding fibromuscular and fibroadipose tissue, adjacent to thick-walled vessels and fibrotic stroma. The overall appearance is consistent with a deeply infiltrative Müllerian-type carcinoma involving the abdominal wall. B. (H&E × 100) Area of abdominal wall endometriosis composed of benign endometrial-type glands embedded in fibrous stroma with an associated chronic inflammatory infiltrate, in close proximity to the invasive carcinoma. This relationship supports malignant transformation of pre-existing abdominal wall endometriosis according to the Sampson and Scott criteria. C. (H&E × 100) View demonstrating complex papillary and tubulocystic architecture lined by atypical epithelial cells with clear to eosinophilic cytoplasm and enlarged nuclei, typical of clear cell carcinoma arising in an endometriosis-associated abdominal wall lesion. D. (H&E × 400) View highlighting tubulocystic and papillary structures lined by a single layer of cuboidal to hobnail tumor cells with clear cytoplasm and conspicuous nuclear atypia. These features are characteristic of Müllerian-type clear cell carcinoma. E. (H&E × 200) View of solid-predominant areas of the abdominal wall clear cell carcinoma composed of sheets and nests of polygonal cells with abundant clear to finely granular cytoplasm and pleomorphic nuclei. The combination of papillary, tubulocystic, and solid patterns is typical of clear cell carcinoma associated with endometriosis. (A, B) Post-treatment pelvic MRI images. Image A (axial T2-weighted) and image B (sagittal T2-weighted) demonstrate findings consistent with previous surgery, including removal of the abdominal wall mass and total abdominal hysterectomy with bilateral salpingo-oophorectomy. A fluid collection is noted at the surgical site, consistent with postoperative change. Clinical timeline of diagnosis and treatment.

Clear cell carcinoma (CCC) arising from abdominal wall endometriosis (AWE) is an exceptionally rare endometriosis-associated malignancy, usually linked to prior obstetric or gynecologic surgery [ 1 – 3 ] . Malignant transformation occurs in roughly 0.7–1.0% of endometriosis cases – usually ovarian – while primary abdominal wall involvement is uncommon and may be associated with delayed diagnosis, large tumor burden, and nodal metastases [ 4 – 6 ] . HIGHLIGHTS Clear cell carcinoma can arise from long-standing cesarean-scar endometriosis after a prolonged latency. Rapid growth, solid components, and lymphadenopathy in abdominal wall endometriosis should raise suspicion of malignant transformation. Preoperative biopsy may be misleading due to tumor heterogeneity, making the definitive diagnosis reliant on excisional pathology. Multimodal management with complete cytoreductive surgery and platinum-based chemotherapy, with or without targeted therapy, is essential for optimal outcomes. HIGHLIGHTS Clear cell carcinoma can arise from long-standing cesarean-scar endometriosis after a prolonged latency. Rapid growth, solid components, and lymphadenopathy in abdominal wall endometriosis should raise suspicion of malignant transformation. Preoperative biopsy may be misleading due to tumor heterogeneity, making the definitive diagnosis reliant on excisional pathology. Multimodal management with complete cytoreductive surgery and platinum-based chemotherapy, with or without targeted therapy, is essential for optimal outcomes. Histologically, these tumors typically meet Sampson’s and Scott’s criteria and show clear cell morphology with a Müllerian immunophenotype, including CK7+, PAX8+, and frequent HNF1B and Napsin A expression [ 4 , 7 – 10 ] . CCC is one of the main histologic subtypes of endometriosis-associated malignancy, alongside endometrioid carcinoma [ 4 , 5 , 11 , 12 ] . No standardized protocol exists because of the rarity of this disease. Most authors recommend wide abdominal wall resection with adequate margins and reconstruction as needed, hysterectomy and bilateral salpingo-oophorectomy to exclude a Müllerian primary, and regional lymphadenectomy when nodes are radiologically suspicious [ 5 , 13 , 14 ] . Adjuvant platinum-based chemotherapy, usually carboplatin plus paclitaxel, is commonly used, with bevacizumab or radiotherapy reported in selected high-risk patients [ 15 , 16 – 18 ] . We report a rare case of clear-cell carcinoma arising from long-standing cesarean-scar endometriosis that was initially misclassified on core biopsy as metastatic serous carcinoma. The patient was managed with neoadjuvant chemotherapy, extensive cytoreduction, adjuvant chemotherapy, and maintenance bevacizumab. This report follows the SCARE checklist [ 19 ] .

CCC arising from AWE is exceptionally rare, with fewer than 50 cases reported. Most patients have a history of cesarean section or other gynecologic surgery, with a typical latency of 15–20 years between surgery and malignant presentation [ 1 , 5 , 7 ] . Our patient developed carcinoma approximately 20 years after cesarean delivery. This prolonged interval emphasizes the importance of maintaining clinical suspicion in women with a progressively enlarging abdominal wall mass arising within a previous surgical scar. Most patients present with a progressively enlarging, painful mass at or near a previous incision, sometimes with cyclical pain in earlier stages, and constitutional symptoms in advanced disease [ 20 – 23 ] . In this case, constitutional symptoms, nodal enlargement, and elevated levels of CA-125 and CA 19-9 suggested an aggressive process. Although CA-125 lacks specificity, its elevation together with suspicious imaging findings may support further investigation and careful staging. The differential diagnosis includes benign AWE, desmoid-type fibromatosis, soft tissue sarcoma, metastatic carcinoma, suture granuloma, incisional hernia, and gynecologic malignancy extending to the abdominal wall. Imaging findings suggestive of malignant transformation include rapid growth, irregular margins, solid components, marked enhancement, necrosis, and regional lymphadenopathy [ 1 – 8 , 13 , 14 , 21 ] . The hemorrhagic cystic foci adjacent to the enhancing abdominal wall mass, and the necrotic external iliac lymphadenopathy in this patient, warranted timely biopsy and multidisciplinary staging. A key feature of this case was the discrepancy between the core biopsy and the final surgical pathology. The core biopsy suggested metastatic serous carcinoma, whereas the resection specimen demonstrated a CCC arising in AWE. Tumor heterogeneity and sampling limitations likely explain this discordance, particularly when benign endometriosis, atypical endometriosis, and invasive carcinoma coexist. Definitive diagnosis should integrate clinical, radiologic, histopathologic, and immunohistochemical findings rather than rely solely on limited biopsy material. Histopathologically, abdominal wall CCC arising in endometriosis generally fulfills Sampson’s criteria and Scott’s additional criterion, demonstrating endometriosis in close relationship to the malignancy [ 9 , 10 , 21 ] . In our patient, benign endometrial glands adjacent to invasive CCC and the absence of a primary malignancy in the uterus, ovaries, or fallopian tubes confirmed the abdominal wall as the site of origin. These findings support malignant transformation of pre-existing scar endometriosis. Because prospective trials are lacking, no standardized treatment guidelines exist, and management is extrapolated from gynecologic CCC and published case reports [ 1 , 6 – 8 , 23 ] . Most authors recommend wide en bloc excision of the abdominal wall mass with adequate margins, sometimes requiring resection of the rectus muscle and fascia with mesh or flap reconstruction, together with hysterectomy and bilateral salpingo-oophorectomy to exclude other primary sites [ 1 – 8 , 13 , 14 , 17 , 18 , 21 – 23 ] . When regional nodes are radiologically suspicious, lymphadenectomy is reasonable because nodal metastasis has been associated with poorer outcomes [ 2 – 4 ] . Our patient underwent neoadjuvant carboplatin-paclitaxel, complete cytoreduction, pelvic lymphadenectomy, and adjuvant chemotherapy with maintenance bevacizumab, achieving complete macroscopic and radiologic remission. Platinum-based chemotherapy, most commonly with carboplatin plus paclitaxel, is frequently used in reported abdominal wall CCC cases [ 1 – 8 , 12 – 14 , 17 , 18 , 21 – 23 ] . Bevacizumab has been incorporated into some clear cell cases, suggesting a potential benefit from angiogenesis inhibition, although evidence remains limited [ 5 , 7 , 8 , 12 – 14 , 16 – 18 , 21 – 24 ] . Radiotherapy has also been used selectively for close or multifocal margins, large tumors, or nodal disease to reduce locoregional recurrence [ 1 – 8 , 12 – 14 , 17 , 18 , 21 – 23 ] . Despite aggressive multimodal treatment, prognosis remains guarded, with local recurrence and distant metastases – particularly to the lymph nodes, lungs, and liver – being reported in the literature [ 1 – 8 , 13 , 14 , 17 , 20 – 23 ] . However, patients who achieve complete cytoreduction and receive adjuvant platinum-based chemotherapy, with or without bevacizumab or radiotherapy, can experience durable disease control, as suggested by recent case reports with follow-up of 20–30 months or longer [ 1 – 8 , 12 – 14 , 16 – 18 , 20 – 23 ] . Long-term surveillance with periodic imaging and CA-125 monitoring is reasonable because late recurrence can occur and available data are insufficient to define optimal follow-up intervals [ 1 – 8 , 13 , 14 , 17 , 20 – 23 ] . The main limitation is the single-case design, which limits the generalizability of treatment recommendations. Preoperative clinical photographs, intraoperative images, and gross pathological specimen photographs were unavailable. Nevertheless, the case illustrates important diagnostic pitfalls, multidisciplinary management, and a favorable medium-term outcome. Improved understanding of the molecular features of endometriosis may help identify patients at higher risk of malignant transformation, including those at uncommon sites, such as the abdominal wall.

Women with a history of cesarean section who develop a rapidly enlarging, scar-associated abdominal wall mass years later should be evaluated for malignant transformation of endometriosis. Early recognition, multidisciplinary assessment, complete cytoreductive surgery, and appropriate systemic therapy may improve outcomes, while prolonged surveillance remains important because of the potential for late recurrence.