Case 5 Female, 85 years. Tumour skin of lower armShow diagnosis & comments
Lentigo maligna melanoma, massive nodular outgrowth
This striking, sharply circumscribed, nonpigmented, mitotically active spindle cell tumour of the skin was initially considered elsewhere to be some type of spindle cell sarcoma. However, the adjacent skin shows lentigo maligna. Immunohistochemistry showed positivity for Melan-A, S-100 and, focoally, HMB-45.
When confronted with a cutaneous (or indeed lymph node) spindle cell tumour of which the diagnosis is not immediately apparent, it is always wise to consider the possibility of a melanocytic tumour. Usually, immunhistochemistry is unequivocal, though it should be borne in mind that desmoplastic melanoma is generally negative for most melanocytic markers (including HMB45, MITF, Melan-A and tyrosinase).