A 65-year-old woman presents with a pruritic, erythematous, eczematous plaque on the vulva. Biopsy shows large cells with pale cytoplasm and vesicular nuclei scattered through the epidermis, predominantly in the basal and parabasal layers. Immunohistochemistry is CK7 positive and S100 negative. What is the most likely diagnosis?

• A Extramammary Paget disease ✓
• B Vulvar intraepithelial neoplasia (VIN)
• C Malignant melanoma of the vulva
• D Mycosis fungoides

Explanation

Extramammary Paget disease of the vulva shows large pale Paget cells infiltrating the epidermis, typically CK7 positive and S100 negative. It must be distinguished from malignant melanoma (S100 positive) and vulvar squamous cell carcinoma in situ (VIN, which lacks the pale Paget cells). Extramammary Paget disease is an intraepidermal adenocarcinoma, often associated with underlying internal malignancies in 25-30% of cases (rectal, urothelial).

Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.