Abstract

While collision tumors involving melanoma and basal cell carcinoma (BCC) are uncommon, neoplasms with intermingled carcinoma and melanoma are exceptionally rare. We report a case of a 76-year-old male with a history of stage IB melanoma of the upper back and multiple non-melanoma skin cancers who presented for routine surveillance skin exam with a non-healing, evolving lesion of the left neck over several months. On exam, an approximately 1 cm pink pearly papule with focal central pigment and erosion was identified with high clinical suspicion for a BCC. A shave biopsy of the lesion was obtained with H&E stained sections showing a predominance of basaloid cells budding from the undersurface of the epidermis and forming nodular and angulated islands within the dermis with overlying erosion. Single cell necrosis, peripheral palisading of tumor nodules, and retraction artifact were seen. On further examination, melanoma in-situ was identified within the tumor, extending focally into the adjacent epidermis. SOX-10 and Melan-A immunohistochemical stains (IHC) highlighted confluent and nested growth of atypical melanocytes and pagetoid spread in the epidermis at the periphery of the lesion and throughout the BCC. Lesional melanocytes expressed PRAME by IHC. The Breslow thickness of the invasive basomelanocytic tumor was at least 0.8 mm with involvement of the deep margin, although the biologic significance of tumor staging in these cases is uncertain. Basomelanocytic tumors present a challenge in both diagnostic evaluation and clinical management, and differentiation of combined tumors from collision tumors can be problematic. Further study of these rare but interesting neoplasms is needed to improve understanding of their pathogenesis and biologic behavior, and they should serve to remind dermatopathologists to examine even seemingly routine BCCs with care.

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