Track: Case Reports

Abstract:

A 56-year-old male presented with a firm, 0.8 cm brown papule on the right scalp. Clinical differential diagnoses included intradermal nevus, keloid, and other scarring processes. A shave biopsy revealed nodular basal cell carcinoma (BCC) with focal keratinization and prominent intratumoral pigmentation. Histologic evaluation demonstrated basaloid nests with peripheral palisading, mucinous stroma, and numerous dendritic melanocytes within tumor islands. The overlying epidermis was unremarkable. Adjacent dermis contained dense aggregates of melanophages extending to within one high-power field of the deep margin, without associated melanocytic proliferation. Immunohistochemistry for SOX10 confirmed melanocytes restricted to the BCC nests, absent in the dermis. The intratumoral melanocytes lacked cytologic atypia and were interpreted as a reactive proliferation to local tumor-derived signals. The dermal melanophages were consistent with tumoral melanosis, a phenomenon classically associated with regressed melanoma but not previously reported in conjunction with BCC. This unusual combination of findings posed a significant diagnostic challenge, especially in a small biopsy. The presence of tumoral melanosis raised concern for regressed melanoma, which was excluded through careful histologic and immunophenotypic evaluation. We propose that local tumor-induced stimulation of melanocytes, followed by melanin release and macrophage uptake, accounts for the adjacent tumoral melanosis. This case expands the histologic spectrum of pigmented BCC and illustrates how benign intratumoral melanocytic activation can result in secondary tumoral melanosis. Awareness of this phenomenon is critical to avoid misdiagnosis and guide appropriate clinical management.

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Andrzej Slominski