Clinicopathologic and Molecular Analyses of 2 Basomelanocytic Tumors and Literature Review

Basomelanocytic tumors are rare cutaneous neoplasms characterized by an intimate admixture of basal cell carcinoma and melanoma. Although basal cell carcinoma (BCC) and melanoma are commonly encountered individually, only a limited number of basomelanocytic tumors have been documented. We report the clinical and histologic features and molecular findings of 2 combined basomelanocytic tumors: 80-year-old man and 91-year-old-man, presented with lesions on the left upper lip and left forehead, respectively. The first tumor consisted of a close admixture of BCC, highlighted by p63 and keratin immunostains, and melanoma, highlighted by Melan-A and SOX10, with abundant melanoma in situ within the lobules of BCC. The second tumor exhibited 2 different neoplastic populations: 1 component of a nodular proliferation of basaloid epithelial nests with peripheral palisading, characteristic of BCC and stained positive for keratin 5/6, keratin 17, and p63. Scattered within these basaloid nests were melanocytes highlighted by Sox10, Melan-A, MiTF, and HMB-45. Molecular analyses of Case 1 show 11 identical variants with similar allelic frequencies detected in both the nodules of invasive melanoma and the remaining surrounding basal cell carcinoma with admixed melanoma cells. In addition, high-level NRAS amplification, and variants of KDR and TRAF7 variants were restricted to the nodules of invasive melanoma, possibly reflecting molecular progression. CDKN2A and PCTH1 mutations, frequently detected in melanoma and basal cell carcinoma, respectively, were detected in the second case. The presence of 2 components with distinct immunoprofile yet with some common genetic aberration suggests that basomelanocytic tumors may arise from a common progenitor.