Pigmented and nested sebomatricoma or seborrheic keratosis with sebaceous differentiation?

Recently, the term sebomatricoma has been proposed as the most appropriate denomination to avoid controversial and confusing terms and to encompass all benign neoplasms with sebaceous differentiation. We report on two specimens that may be interpreted as examples of two new histopathologic patterns in sebomatricoma, namely, pigmented and nested sebomatricoma, or as seborrheic keratosis with sebaceous differentiation. The first case consisted of a neoplasm composed of basaloid immature cells with features of sebaceous differentiation in the form of clusters of sebocytes and sebaceous ducts, in addition to the proliferation of dendritic melanocytes arranged as solitary units scattered through the neoplastic aggregations of immature germinative sebaceous cells. The second case, in addition to the proliferation of single dendritic melanocytes as the first case, showed well-defined nests of basaloid and heavily pigmented germinative sebaceous cells connected to the skin surface and numerous sebaceous ducts. In the first case, the pigmented nature of the lesion was the most striking histopathologic characteristic, whereas the nested pattern was remarkable in the second one. Immunohistochemical investigations demonstrated positivity of cytokeratin MNF116 in neoplastic aggregations of germinative sebaceous cells, whereas the clusters of mature sebocytes and sebaceous ducts expressed epithelial membrane antigen positivity. S-100 protein made evident the scattered dendritic melanocytes, but neoplastic cells resulted negative.