Trichoblastoma — SCE Dermatology MCQ

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HardSkin CancerTrichoblastomaSCE Dermatology

A 60-year-old man presents with a slowly growing nodule on his scalp. Biopsy shows a well-circumscribed dermal tumour composed of basaloid cells forming hair follicle-like structures with papillary mesenchymal bodies. It is BerEP4-negative (distinguishing it from BCC). What is the diagnosis?

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Correct answer: A — Trichoblastoma

The diagnosis is trichoblastoma: a benign adnexal tumour showing follicular germinative differentiation. The key exam clues are a slow-growing scalp nodule, a well-circumscribed dermal basaloid tumour, formation of primitive hair follicle-like structures, and papillary mesenchymal bodies, which support a benign hair-germ tumour. BerEP4-negativity in the stem argues against basal cell carcinoma, which is typically BerEP4-positive and more often shows epidermal connection, stromal retraction clefts, mucinous stroma, cytological atypia and mitotic activity. Cylindroma shows jigsaw-puzzle islands with hyaline basement membrane material; spiradenoma is a painful adnexal tumour with dual cell populations and lymphocytes; pilomatrixoma shows matrical differentiation with shadow/ghost cells and calcification. Therefore the best answer is trichoblastoma.

Reference: WHO Classification of Tumours Editorial Board. WHO Classification of Skin Tumours, 5th ed., Volume 12. IARC; 2025. https://publications.iarc.who.int/Book-And-Report-Series/Who-Classification-Of-Tumours/Skin-Tumours-2025