Primary Clear Cell Adenocarcinoma of the Vulva: A Case Study With Mutation Analysis and Literature Review.

Primary vulvar clear cell carcinoma (CCC) is extremely rare. In this article, we report a primary vulvar CCC along with immunohistochemical and gene mutation analyses results and literature review to discuss the clinicopathological features and tumorigenesis of this rare tumor. A 70-year-old (gravida 2 para 2) Japanese woman complained of bleeding from a vulvar mass at a past episiotomy site. A 1.8 × 1.8 × 0.5 cm exophytic sessile mass was present on the vestibular area inside the left labium minora. Radical local excision of the tumor and resection of the inguinal lymph nodes on both sides were performed. Histopathology revealed a vulvar CCC with immunohistochemical positivity for PAX8, HNF-1β, ER, and CA125, and negativity for p16, CD10, GATA3, PTEN, and PAX2, suggesting its Müllerian origin. No lymph node metastasis was observed. The tumor was a 5-mm exophytic growth without deep stromal invasion; thus, it was difficult to measure the invasion depth assuming a squamous cell carcinoma. To investigate pathogenic/oncogenic mutations in 50 cancer-related genes, we used the AmpliSeq Cancer Hotspot Panel. However, no pathogenic/oncogenic mutations were detected. Literature review revealed that most cases of vulvar CCC are associated with vulvar endometriosis. In particular, cases with clinically evident endometriosis at the episiotomy scar should be carefully observed. Evidence-based pathological stages of vulvar adenocarcinoma including CCC remain to be established owing to its rarity, with nationwide or global accumulation of cases required in future.