Dermal squamo-melanocytic tumor: A unique biphenotypic neoplasm of uncertain biological potential

We report four cases of an unusual cutaneous squamomelanocytic neoplasm wit h histological features of malignancy and uncertain biological potential. T hese tumors developed on the face of middle-aged and older adults. Clinical ly, a purple-black nodule ranged in size from 3 to 10 mm in maximum diamete r. After complete excision, neither recurrence nor metastasis has been obse rved (mean follow-up time, 3.25 years). Histologically, a discrete dermal n odule surrounded by a fibroblastic stroma was composed of large islands of mitotically active atypical epithelioid cells. The nodule was not connected to the epidermis in three of four cases. Two types of cells were either di ffusely admired or clustered in small groups within the nodule. Small, atyp ical, epithelioid cells containing finely granular brown pigment, proven to be melanin, constituted the first cell type. The second type consisted of atypical squamoid cells, some with abundant pink cytoplasm, giving rise to squamous pearls. A lentigo maligna was present in one case. The remaining t hree cases had neither significant intraepidermal melanocytic nor keratinoc ytic atypia. Immunohistochemical studies indicated that the melanin-contain ing epithelioid cells expressed S-100 antigens, and the squamoid cells expr essed cytokeratins. A small population of tumor cells did not label with ei ther of the antibodies. These four tumors (along with a previously reported, apparently identical t umor arising in the setting of lentigo maligna) represent a unique biphasic dermal neoplasm with histological features of malignancy but, at this time , uncertain biological behavior. Although none have recurred or metastasize d, the follow-up time is too short in our estimation to guarantee a benign course. These neoplasms are easily recognized by their characteristic featu res. Further follow-up evaluations should allow determination of their biol ogic potential. Hmi PATHOL 30:525-529. Copyright (C) 1999 by W.B. Saunders Company.