RARE PRESENTATION OF PRIMARY MUCINOUS ADENOCARCINOMA, MAMMARY TYPE, OF THE VULVA

Objectives: Primary mucinous adenocarcinoma of the vulva is an extremely rare disease, comprising only 1% of all vulvar cancers, with most primary vulvar cancers diagnosed as squamous cell carcinoma (90%). Primary mucinous adenocarcinoma of the vulva tends to arise from normal glandular structures, embryonic remnants, and ectopic tissues. We herein present a case of a 57-year-old G3P2012, who had a 3.0-cm cystic tumor of the left labium majus. Gynecologic exam showed a 1.0-cm lump on the vulva that had been persistent for months. The patient denied any pain, pruritus, or discoloration. She underwent a vulvar biopsy with a histologic diagnosis of moderately differentiated mucinous adenocarcinoma, mammary type. On immunohistochemical analysis, mucicarmine and PAS-D highlighted the abundant mucin present in the tumor. Tumor cells were diffusely positive for Cytokeratin-7 (CK7), GATA3, estrogen receptor (ER), and progesterone receptor (PR), which is the immunophenotype associated with primary breast carcinoma. The tumor was negative for HER2. The tumor also stained negatively for CA125, Calretinin, and PAX8, excluding ovarian cancer origin, and negatively for CDX2 and CK20, excluding adenocarcinoma of the gastrointestinal tract. TTF-1 was also negative, thereby excluding lung origin. These resulting stains showed features which raised the possibility of metastatic breast cancer vs. an adenocarcinoma of mammary type, primary to the vulvar region. Both tumors can have identical staining and morphologic features. Therefore, the distinction is made on clinical work up. A breast work-up included mammography and core biopsy of a hypoechoic avascular breast mass and a suspicious axillary lymph node with negative findings confirming the vulva as the primary site. The patient then underwent a partial radical hemi-vulvectomy and sentinel pelvic node biopsy. The histologic diagnosis of the resection specimen was primary mucinous adenocarcinoma of the vulva, mammary type, with a negative sentinel node. This patient’s vulvar cancer likely originated from ectopic breast tissue, given the morphologic features and immunohistochemical profile. To the best of knowledge, there has only been one reported case of a primary mucinous adenocarcinoma of the vulva arising from ectopic breast tissue, making this the second reported case. Our patient is doing well 1 month after surgery and is undergoing postoperative tamoxifen therapy. Due to the rare nature of primary mucinous adenocarcinoma of the vulva, mammary type, standardized postsurgical treatment and outcomes are unknown. Therefore, tumor tissue has been sent to Caris for genomic testing and will hopefully elucidate a targetable genomic profile for this exceptionally rare tumor.

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