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Abstract

Aggressive digital papillary adenocarcinoma (ADPA) is a rare malignant tumor of eccrine sweat glands, often affecting the fingers and toes. These tumors have high recurrence and metastasis rates. They are frequently misdiagnosed due to their clinical resemblance to ganglionic cysts or pyogenic granulomas and their histologic similarity to benign adnexal neoplasms. We report an unusual vulval analogue of ADPA. A 48-year-old woman with a history of a left vulvar cyst presented after four months of enlargement. Initial biopsy suggested eccrine spiradenoma, but dermatopathology review revealed an atypical basaloid neoplasm with ductal differentiation, cytologic atypia, and atypical mitoses. Immunohistochemistry revealed CK7 and diffuse Sox-10 expression, with block-type p16 positivity; the BRAF VE was negative. Given these atypical features, complete excision was advised. Partial vulvectomy revealed a well-circumscribed dermal nodule with basaloid proliferation, focal papillary architecture, and back-to-back glandular elements. P63 and smooth muscle myosin highlighted a preserved myoepithelial layer. HPV42 in-situ hybridization was positive. The final diagnosis was vulval analog of aggressive digital papillary adenocarcinoma. Margins, sentinel lymph node, and follow-up PET/CT were negative. She remains in remission under surveillance. This case adds to the limited reports of genital ADPA, a rare malignancy. The vulvar lesion was initially misdiagnosed as a benign adnexal neoplasm, likely due to its unusual location. HPV-42 positivity is a highly specific and sensitive diagnostic marker; however, it is not widely available for testing. In such cases, cytologic and architectural atypia, p16 block staining, and absence of BRAF mutations can aid in diagnosing extra-acral ADPA.