A 62-year-old man has a firm, skin-coloured, scar-like plaque on the scalp that was initially diagnosed as a keloid. Biopsy shows spindle-shaped melanocytes infiltrating the dermis in a fibrotic stroma, with perineural invasion. Immunohistochemistry is positive for S100 and SOX10 but negative for HMB45 and Melan-A. The MOST likely diagnosis is:

• A Desmoplastic melanoma ✓
• B Dermatofibrosarcoma protuberans
• C Sclerosing blue naevus
• D Neurofibroma

Explanation

Desmoplastic melanoma is a spindle-cell melanoma variant that mimics a scar or neuroma clinically. It characteristically loses expression of HMB45 and Melan-A but retains S100 and SOX10 positivity, which are the diagnostic markers here. Neurotropism explains its high rate of local recurrence. DFSP is CD34 positive and S100 negative, which eliminates option B.

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.