A rare case of multifocal vulvar carcinoma of mammary gland type (AMGT) with mucinous features: Differential diagnosis and literature review

A 78-year-old woman presented with a 3-year history of a nodule on the right labia minora, recently noted to be increasing in size ( Fig. 1 A). Computed tomography imaging did not demonstrate pelvic lymphadenopathy. The patient had a complex gynecologic history notable for endometriosis, vaginal vault prolapse status post-robotic sacrocolpopexy and hysterectomy, urinary stress incontinence, urinary tract infections, and Bartholin gland cyst status post excision. Fig. 1 (A) Clinical appearance of the right vulvar (blue arrow) and supraclitoral (green arrow) nodules. (B) Gross image of the excised right vulvar nodule. (C) Sectioning reveals a solid and tan-white cut surface. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.) (A) Clinical appearance of the right vulvar (blue arrow) and supraclitoral (green arrow) nodules. (B) Gross image of the excised right vulvar nodule. (C) Sectioning reveals a solid and tan-white cut surface. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.) On examination, the right vulvar nodule was firm, irregular, mobile, and located below the skin of the right vulva. It measured 3  cm in length, 1.5  cm in width, and 1.5  cm in depth, extending from the right upper labia to the interlabial fold adjacent to the clitoris ( Fig. 1 A). During examination, an additional supra-clitoral nodule was identified and measured 0.7  cm in length, 0.5  cm in width, and 0.4  cm in depth. The two nodules were 3  cm apart ( Fig. 1 A). The vulvar and supra-clitoral nodules were both excised. Due to the abnormal gross appearance of the large nodule, the specimen was sent to pathology for frozen section evaluation. This was preliminarily reported as mucinous adenocarcinoma with positive margins. The gynecology oncology service was consulted intraoperatively and a wide local excision was performed. The excised right vulvar nodule was a tan-pink and firm mass surrounded by a thin layer of fibrous tissue, measuring 2.1x1.8x1.1  cm. The excised supra-clitoral nodule was a tan-white and firm mass measuring 0.7x0.5x0.4  cm. The cut surface was tan-yellow, solid, and fleshy ( Figs. 1 B and 1C). Touch preparation of the right vulvar nodule revealed clusters of neoplastic epithelial cells within a mucinous background ( Fig. 2 A). Histological sections demonstrated an invasive mucinous adenocarcinoma consisting of nests and cords of tumor cells within abundant extracellular mucin ( Fig. 2 B). There was moderate nuclear atypia, scattered mitoses ( Fig. 2 C), focal tumor necrosis, and an intravascular tumor thrombus ( Fig. 1 D). Fig. 2 (A) Touch preparation of the right vulvar nodule demonstrating clusters of malignant epithelial cells with abundant mucin (hematoxylin and eosin [H&E) stain, 10X). (B, C) Histological sections of the right vulvar nodule showing invasive mucinous adenocarcinoma (H&E stain; B, 4X; C, 20X). (D) Intravascular tumor thrombus (H&E stain, 10X). (A) Touch preparation of the right vulvar nodule demonstrating clusters of malignant epithelial cells with abundant mucin (hematoxylin and eosin [H&E) stain, 10X). (B, C) Histological sections of the right vulvar nodule showing invasive mucinous adenocarcinoma (H&E stain; B, 4X; C, 20X). (D) Intravascular tumor thrombus (H&E stain, 10X). The supra-clitoral nodule showed DCIS arising from benign mammary-like glands ( Figs. 4 A and 4B). Tumor cells exhibited moderate nuclear atypia (grade 2 of 3) with focal central necrosis. No invasive carcinoma was identified. The overlying skin showed no pagetoid lesions, dysplasia, or malignancy. The mucinous adenocarcinoma of the right vulvar nodule demonstrated immunoreactivity for CK7 (diffuse, Fig. 3 A), CK20 (patchy), CK5/6 (partial), GATA3 (diffuse, Fig. 3 B), ER (100%, Fig. 3 C), PR (50%, Fig. 3 D), and GCDFP-15 (focal). The tumor was immunohistochemically negative for PAX8 ( Fig. 3 E) and PSA ( Fig. 3 F). Immunohistochemical staining for HER2 overexpression and FISH for HER2 gene amplification were also negative. Collectively, these findings support a diagnosis of a mucinous variant of AMGT. Fig. 3 Immunohistochemical stains of the mucinous adenocarcinoma demonstrate positive immunoreactivity for (A) CK7 (diffuse; 4X), (B) GATA3 (diffuse; 10X), (C) ER (diffuse; 100%; 20X), and (D) PR (positive; 50%; 20X). Immunohistochemical stains for (E) PAX8 (20X) and (F) PSA (20X) were negative. Immunohistochemical stains of the mucinous adenocarcinoma demonstrate positive immunoreactivity for (A) CK7 (diffuse; 4X), (B) GATA3 (diffuse; 10X), (C) ER (diffuse; 100%; 20X), and (D) PR (positive; 50%; 20X). Immunohistochemical stains for (E) PAX8 (20X) and (F) PSA (20X) were negative. The DCIS of the supra-clitoral nodule exhibited an immunohistochemical profile like that of the right vulvar mucinous adenocarcinoma, including diffuse positivity for GATA3 ( Fig. 4 C) and CK7 ( Fig. 4 D), and negative staining for PAX8 ( Fig. 4 I) and CK20 ( Fig. 4 J). Immunohistochemical staining for p63 ( Fig. 4 E), heavy chain smooth muscle myosin ( Fig. 4 F), CK5/6 ( Fig. 4 G), and CK14 ( Fig. 4 H) highlighted preserved myoepithelial cells around the DCIS. Fig. 4 (A-B) High-grade DCIS arising from mammary-like glands of the vulva showing central necrosis. Arrows depict benign mammary-like tissue (H&E stain, 4X and 10X). Immunohistochemical stains demonstrate positive immunoreactivity in DCIS for (C) GATA3 (10X) and (D) CK7 (4X). Immunohistochemical staining for (E) p63 (10X), (F) heavy-chain myosin (10X), (G) CK5/6 (10X), and (H) CK14 show preserved myoepithelial cells around DCIS (10X). Arrows in G and H highlight the mosaic staining pattern for CK14 and CK 5/6 in benign mammary-like glands, in contrast to loss of immunoreactivity in DCIS. Immunohistochemical stains for (I) PAX8 (10X) and (J) CK20 (10X) were negative. (A-B) High-grade DCIS arising from mammary-like glands of the vulva showing central necrosis. Arrows depict benign mammary-like tissue (H&E stain, 4X and 10X). Immunohistochemical stains demonstrate positive immunoreactivity in DCIS for (C) GATA3 (10X) and (D) CK7 (4X). Immunohistochemical staining for (E) p63 (10X), (F) heavy-chain myosin (10X), (G) CK5/6 (10X), and (H) CK14 show preserved myoepithelial cells around DCIS (10X). Arrows in G and H highlight the mosaic staining pattern for CK14 and CK 5/6 in benign mammary-like glands, in contrast to loss of immunoreactivity in DCIS. Immunohistochemical stains for (I) PAX8 (10X) and (J) CK20 (10X) were negative. The morphologic and immunohistochemical features of both vulvar tumors are consistent with primary vulvar AGMT. Postoperative magnetic resonance imaging showed no suspicious lesions in the breasts or gastrointestinal tract, rendering the diagnosis of metastatic carcinoma unlikely. The possibility of primary vulvar adenocarcinomas arising from Bartholin or Skene’s glands was considered but not supported by morphological or immunohistochemical findings, including strong immunoreactivity to GATA3 and absence PSA immunoreactivity.

Shandice B. Waugh: Writing – review & editing, Writing – original draft, Formal analysis, Conceptualization. Henrietta O. Maku: Writing – review & editing, Writing – original draft, Investigation, Data curation, Conceptualization. Danielle D. Antosh: Writing – review & editing, Visualization, Supervision, Methodology, Data curation. Sarah K. Rozycki: Writing – review & editing, Visualization, Data curation. Aparna A. Kamat: Writing – review & editing, Visualization, Supervision, Data curation. Ekene I. Okoye: Writing – review & editing, Supervision, Methodology, Investigation. Donna M. Coffey: Writing – review & editing, Supervision, Methodology, Investigation. Micheal T. Deavers: Writing – review & editing, Supervision, Methodology, Investigation. Mary R. Schwartz: Writing – review & editing, Writing – original draft, Validation, Supervision, Methodology, Investigation. Yimin Ge: Writing – review & editing, Writing – original draft, Visualization, Supervision, Methodology, Data curation, Conceptualization.

This manuscript is submitted as a case report. At our institution ethical approval is not indicated for case reports.

The authors received no financial support for this manuscript.

Written patient consent for both participation and publishing the clinical and pathologic findings in this case report has been obtained. The patient’s anonymity is protected.

In summary, AMGT is a rare primary vulvar adenocarcinoma, with 54 cases previously reported to date. We report an additional case involving a rare mucinous subtype of AMGT with concomitant DCIS and benign mammary-like tissue. These tumors are often seen in elderly women with an average age of 62 years old. Accurate diagnosis of AMGT relies on awareness of this rare entity, its typical “milk line” location, and morphological and immunohistochemical findings analogous to breast counterparts. Coexistence of adenocarcinoma with mammary-like glands, benign mammary-like lesions, or DCIS strongly supports a diagnosis of AGMT.

Primary vulvar AMGT is a rare gynecologic cancer with only 54 previously reported cases ( Naseer et al., 2011 , Castro and Deavers, 2001 , Greene, 1936 , Hendrix and Behrman, 1956 , Guerry and Pratt-Thomas, 1976 , Cho et al., 1985 , Simon et al., 1988 , Rose et al., 1990 , Pelosi et al., 1991 , Di Bonito et al., 1992 , Bailey et al., 1993 , C. vdPS, 1994 , Levin et al., 1995 , Kennedy et al., 1997 , Irvin et al., 1999 , Gorisek et al., 2000 , Neumann et al., 2000 , Chung-Park et al., 2002 , Piura et al., 2002 , Yin et al., 2003 , Ohira et al., 2004 , Tanaka et al., 2005 , Abbott and Ahmed, 2006 , Fracchioli et al., 2006 , Intra et al., 2006 , Lopes et al., 2006 , Martinez-Palones et al., 2007 , North et al., 2007 , Tseung and Russell, 2008 , Diniz da Costa et al., 2012 , Bogani et al., 2013 , McMaster et al., 2013 , Meddeb et al., 2014 , Baykal et al., 2015 , Cripe et al., 2015 , Tran et al., 2015 , Villada et al., 2015 , Grewal et al., 2017 , Ishigaki et al., 2017 , Al-Mansouri et al., 2018 , Lopes et al., 2018 , Li et al., 2019 , Ananthula et al., 2020 , Deshmukh et al., 2020 , Farrag et al., 2020 , Kalwiba et al., 2022 , Morais et al., 2022 , Lobrano et al., 2023 , Mansour et al., 2023 , Sandak et al., 2023 , Hu and Tiesinga, 2024 , Tang et al., 2024 , Benito et al., 2013 ). The clinicopathological features of these cases are summarized in Table 1 . The most common histologic subtype of AMGT is invasive ductal carcinoma, but rare cases of lobular, ( Irvin et al., 1999 , Neumann et al., 2000 , Villada et al., 2015 ) mucinous,( Chung-Park et al., 2002 , Yin et al., 2003 , Lopes et al., 2006 , Tang et al., 2024 ) and encapsulated papillary carcinomas ( Tang et al., 2024 ) have also been reported. Patients typically present with an asymptomatic nodule averaging 3.1  cm (range: 1 to 20  cm), although some cases have reported symptoms including pain, discharge, bleeding, ulceration, and dysuria ( Mansour et al., 2023 ). The average age at clinical presentation is 62 years old, with a range of 40 to 88 years. These tumors often express ER (81.3%) and PR (71.8%), with occasional HER2 gene amplification (24.1%) ( Intra et al., 2006 , Meddeb et al., 2014 , Grewal et al., 2017 , Lopes et al., 2018 , Hu and Tiesinga, 2024 ). Positive immunoreactivity to CK7 (95%), GATA3 (91.7%), and mammaglobin (80%) supports breast differentiation of these tumors. Various benign breast lesions have also been identified in vulvar mammary-like glands ( Yin et al., 2003 , Arora et al., 2020 ). The coexistence of AMG, benign mammary-like lesions, or DCIS strongly supports a diagnosis of primary AGMT ( Hu and Tiesinga, 2024 ). Of the 54 previously reported cases, 17 (31.4%) explicitly described benign ectopic breast tissue or mammary-like glands associated with vulvar tumors, and 7 (13%) had concomitant DCIS. Table 1 Clinicopathologic features of primary vulvar adenocarcinoma of mammary-like glands (1–53). Age 40–88 years (mean: 62.6 years) Symptom Pain 16/55 (29.1%) Ulceration 13/55 (23.6%) Bleeding 6/55 (10.9%) Swelling/edema 4/55 (7.3%) Uncommon symptoms: erosion, discharge, erythema, induration, infection, itching and dysuria Tumor location Labium majus 26/55 (47.3%) Labium minus 6/55 (10.9%) Involving both labium majus and minus 3/55 (5.4%) Mons pubis 4/55 (7.3%) Involving both labium minus and clitoris 1/55 (1.8%) Periclitoral 1/55 (1.8%) Introitus 1/55 (1.8%) Unspecified 13/55 (23.6%) Tumor size 1.0 – 20.0 cm (average: 3.1 cm) Histological types Invasive ductal carcinoma 33/55 (60%) Adenocarcinoma, NOS 10/55 (18.2%) Extramammary Paget’s disease 5/55 (9.1%) Mucinous adenocarcinoma 5/55 (9.1%) Lobular carcinoma 3/55 (5.5%) Encapsulated papillary carcinoma 1/55 (1.8%) DCIS 14/55 (25.5% including 9 with invasive carcinoma) Benign mammary-like glands 17/55 (30.1%) Immunohistochemical reactivity Positive: CK7 21/22 (95.5%), GATA3 13/14 (92.8%), ER 40/48 (83.3%), Mammaglobin 8/10 (80%), PR 30/41 (73.1%), S100 1/7 (14.3%), CK20 1/15 (6.7%) Negative: PAX8 0/8 (0%), WT1 0/2 (0%), Melan-A 0/1 (0%) Surgical management Wide local excision 18/54 (33.3%) Radical vulvectomy 15/54 (27.8%) Partial vulvectomy 7/54 (13%) Excisional biopsy 5/54 (9.6%) Hemivulvectomy 2/54 (3.7%) Local excision 3/54 (5.6%) Adjuvant therapy None 18/54 (33.3%) Radiation 18/54 (33.3%) Chemotherapy 18/54 (33.3%) Tamoxifen 16/54 (29.6%) Aromatase inhibitor 12/54 (22.2%) Outcomes Alive at the time of report 7/40 (17.5%) No evidence of disease 20/40 (50%) No disease progression* 2/40 (5%) Recurrence 4/40 (10%) Died of disease 7/40 (17.5%) *The designation of “No disease progression” is used in instances where the original author explicitly classified the patient as having measurable disease with no further progression. The designation of “No evidence of disease” is used to describe cases where there was no residual tumor after resection. Clinicopathologic features of primary vulvar adenocarcinoma of mammary-like glands (1–53). *The designation of “No disease progression” is used in instances where the original author explicitly classified the patient as having measurable disease with no further progression. The designation of “No evidence of disease” is used to describe cases where there was no residual tumor after resection. The mucinous AMGT case described here is exceedingly rare type of AMTG, with only 4 previous cases reported ( Chung-Park et al., 2002 , Yin et al., 2003 , Lopes et al., 2006 , Tang et al., 2024 ). The coexistence of mucinous adenocarcinoma with DCIS and benign mammary-like glands offered an important diagnostic clue for AMGT in this case. When evaluating vulvar adenocarcinomas, it is critical to thoroughly search for mammary-like glands, benign mammary-like lesions, or DCIS-like preinvasive tumors in adjacent tissue. Immunohistochemistry is often needed to confirm breast differentiation and establish the diagnosis of primary vulvar AMGT. Before rendering a diagnosis of primary vulvar AMGT, it is crucial to exclude metastatic mucinous adenocarcinoma from other sites, such as the breast, colon, cervix, endometrium, ovary, pancreas, and genitourinary tract ( Neto et al., 2003 ). Distinguishing AMGT from metastatic breast adenocarcinomas involving the vulva can be difficult using morphology and immunohistochemistry alone; correlation with clinical history and imaging studies is essential for accurate diagnosis ( Morais et al., 2022 ). Identification of tumor-associated mammary-like tissue strongly supports the diagnosis of AMGT. Clinically, treatment of primary vulvar AMGT has been typically modeled after therapies for primary breast carcinomas ( Bogani et al., 2013 ). This can include local excision with sentinel lymphadenectomy in cases with localized disease, or wide local excision/vulvectomy followed by adjuvant chemotherapy, hormone therapy, and/or radiation in cases with advanced disease, positive lymph nodes, or extracutaneous involvement ( Bogani et al., 2013 ). In the case described here, the patient underwent subsequent wide local excision of the vulvar AMGT due to positive margins on the initial local resection, achieving negative final margins. Given the patient’s localized tumor, lymph node dissection was not performed. After review of this case at tumor board, a wide local excision of the supra-clitoral nodule was also performed. At her 1-year follow-up, the patient is well, with no recurrence or additional tumors. HER-2 inhibition with trastuzumab is recommended for patients with HER2-positive AMGT, and hormonal therapy is recommended for patients with ER-positive tumors ( Lopes et al., 2018 , Morais et al., 2022 ). Radiation therapy may also be recommended in cases of extensive disease ( Morais et al., 2022 ). Among reported cases with documented follow-up, many with patients who underwent successful tumor resection along with adjuvant radiation, chemotherapy, or hormonal therapy, most showed no evidence of disease or disease progression at follow-up (28 of 39 cases, 72%). However, some patients experienced progression of disease, with 10% (4 of 39) developed distant metastases and 18% (7 of 39) died from the disease. A few reports have documented molecular abnormalities in primary vulvar AMGT. Lobrano et al described pathogenic mutations in AKT1 (AKT serine/threonine kinase 1) , likely pathogenic mutations in JAK1 (Janus kinase) and KMT2C (lysine-specific methyltransferase 2C), and copy number variations in BRCA1 (Breast Cancer Gene 1) ( Lobrano et al., 2023 ). Another study identified mutations in mammary-like adenocarcinomas similar to those observed in luminal B-type breast cancers, including ERBB2-NAGLU (HER2-N-acetyl-alpha-glucosaminidase) fusion, ESR1-CCDC170 (estrogen receptor gene and coiled-coil domain containing 170) fusion, PIK3CA (phosphatidylinositol-4,5-bisphosphate 3-kinase, catalytic subunit alpha) deletion, p53 deletion, and MYC amplification ( Hu and Tiesinga, 2024 ). Further genetic profiling is needed to better understand the biological, pathogenic, and clinical connections between primary vulvar AMGT and breast cancer.

The differential diagnosis for AGMT is broad, as several primary and metastatic vulvar tumors may histologically mimic AMGT. Accurate diagnosis requires correlation with past medical history (especially prior malignancies) and clinical presentation, including symptoms, location, size, and relation to overlying skin. Familiarity with other primary vulvar tumors can be helpful during diagnostic evaluation. The following primary vulvar tumors are commonly confused with AMGT in differential diagnosis: Bartholin gland carcinomas are rare, representing about 5% of vulvar cancers ( Hill et al., 2010 ). They include squamous cell carcinoma (40%), adenocarcinoma (40%), adenoid cystic carcinomas (15%), and adenosquamous carcinoma (5%) ( Nakamura et al., 2020 ). These tumors are not associated with mammary-like glands or DCIS and are typically negative for breast differentiation markers. Among these tumors, adenoid cystic carcinomas feature a characteristic cribriform pattern with eosinophilic basement membrane-like material within punched-out spaces. Immunohistochemical staining for S100 is often positive in adenocarcinomas and adenoid cystic carcinomas arising from Bartholin glands but is typically negative in AMGTs ( Alyssa Miceli, 2022 , Donato et al., 2017 ). The Skene’s gland, which is homologous to the male prostate gland, can give rise to adenocarcinomas that resemble prostatic adenocarcinoma morphologically, immunohistochemically, and clinically ( Pongtippan et al., 2004 , Tregnago and Epstein, 2018 ). These tumors are generally composed of monotonous cells with pale to eosinophilic cytoplasm and prominent nucleoli. The tumors often adopt a cribriform-predominant pattern akin to Gleason grade 4, although patterns analogous to Gleason grades 3 and 5 have also been reported ( Tregnago and Epstein, 2018 ). The tumor cells are uniquely positive for PSA, prostate-specific acid phosphatase (PSAP), and NKX3 homeobox protein (NKX3.1), and are negative for GATA3 and other breast differentiation markers ( Tregnago and Epstein, 2018 , Me et al., 2021 ). Sebaceous carcinomas of the vulva are very rare, with fewer than a dozen cases reported ( Yamamoto et al., 2021 ). The tumors usually occur in older women (mean age 55.9 years) who present with pruritic and occasionally painful masses ( Wang and Wei, 2023 ). Histologically, these tumors exhibit lobules of tumor cells showing varying degrees of sebaceous differentiation. Sebaceous carcinomas are typically positive for p40 and p63 but negative for carcinoembryonic antigen (CEA) and GCDFP-15, in contrast to carcinomas arising from mammary-like glands ( Xu et al., 2018 , Plaza et al., 2015 , J P et al., 2017 ). Microcystic adnexal carcinomas of the vulva are extremely rare, representing 0.1%–0.5% of vulvar neoplasms, with only three cases reported ( Marchitelli, 2017 , Buhl et al., 2001 , Nahm et al., 2023 ). Histologically, they feature infiltrative proliferation of various proportions of keratocysts in the upper portion of the lesion, nests and cords of smaller epithelial cells in the middle portion, and bi-layered ductal structures in the lower portion, commonly with perineural invasion ( Calonje et al., ). Microcystic adnexal carcinomas are often positive for epithelial membrane antigen (EMA) and CEA in ductal components and p63 in basal cells but negative for CK7 and other breast differentiation markers, which differentiates them from AMGT ( Rollins-Raval et al., 2011 , Hoang et al., 2008 ). Malignant eccrine spiradenomas are one of the rarest tumors arising from sweat glands, with only 5 cases involving the vulva reported ( Catteau et al., 2020 , DM et al., 2006 , Baker et al., 2013 , Chen et al., 2011 , Emam et al., 2012 ). Histologically, these tumors show pleomorphic basaloid cells with prominent nucleoli, abundant mitotic figures, infiltrative growth, necrosis, and lymphovascular and perineural invasion. Tumor cells typically lack breast differentiation markers but are often positive for epidermal growth factor receptor (EGFR) in up to 75% of cases ( Chung-Park et al., 2002 , Catteau et al., 2020 ). Nuclear beta-catenin expression and intraluminal PAS-positive, diastase-resistant material may also help distinguishing this entity from AMGT.

Primary vulvar adenocarcinomas are uncommon gynecologic cancers, accounting for about 1% of all vulvar neoplasms ( Naseer et al., 2011 ). These tumors can present as extramammary Paget’s disease or arise from the sweat glands, Bartholin glands, Skene glands, or mammary-like glands in the anogenital region ( Castro and Deavers, 2001 ). Among these, primary vulvar adenocarcinoma of mammary gland type (AMGT) is exceedingly rare, with limited cases documented in the literature ( Naseer et al., 2011 , Castro and Deavers, 2001 , Greene, 1936 , Hendrix and Behrman, 1956 , Guerry and Pratt-Thomas, 1976 , Cho et al., 1985 , Simon et al., 1988 , Rose et al., 1990 , Pelosi et al., 1991 , Di Bonito et al., 1992 , Bailey et al., 1993 , C. vdPS, 1994 , Levin et al., 1995 , Kennedy et al., 1997 , Irvin et al., 1999 , Gorisek et al., 2000 , Neumann et al., 2000 , Chung-Park et al., 2002 , Piura et al., 2002 , Yin et al., 2003 , Ohira et al., 2004 , Tanaka et al., 2005 , Abbott and Ahmed, 2006 , Fracchioli et al., 2006 , Intra et al., 2006 , Lopes et al., 2006 , Martinez-Palones et al., 2007 , North et al., 2007 , Tseung and Russell, 2008 , Diniz da Costa et al., 2012 , Bogani et al., 2013 , McMaster et al., 2013 , Meddeb et al., 2014 , Baykal et al., 2015 , Cripe et al., 2015 , Tran et al., 2015 , Villada et al., 2015 , Grewal et al., 2017 , Ishigaki et al., 2017 , Al-Mansouri et al., 2018 , Lopes et al., 2018 , Li et al., 2019 , Ananthula et al., 2020 , Deshmukh et al., 2020 , Farrag et al., 2020 , Kalwiba et al., 2022 , Morais et al., 2022 , Lobrano et al., 2023 , Mansour et al., 2023 , Sandak et al., 2023 , Hu and Tiesinga, 2024 , Tang et al., 2024 , Benito et al., 2013 ). Notably, benign and neoplastic mammary-like glands share histologic and immunohistochemical profiles similar to breast tissue. Originally described in 1872 as accessory breast tissue, mammary-like glands were postulated to be analogous to naturally occurring polymastia in mammals such as dogs and pigs ( Hartung, 1872 ). The origin and molecular mechanisms underlying breast tissue formation in the anogenital region remain unclear. One explanation involves the ventral embryonic milk ridge, which extends from the axilla to the medial groin, with the pectoral aspects of the milk ridge persisting to form the left and right breasts ( Skandalakis, 2008 ). Failure of other glands along this ridge to regress may leave remnants capable of developing benign and malignant lesions identical to breast lesions ( Velanovich, 1995 ). More recent theories suggest these glands are normal histologic components of the anogenital region derived from normal eccrine-like glands ( Arora et al., 2020 ). This case report describes an unusual type of AMGT consisting of coexisting mucinous adenocarcinoma and ductal carcinoma in situ (DCIS) in the vulva, a finding rarely documented in the literature ( Tang et al., 2024 ).

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.