Atypical lipomatous tumor/"well-differentiated liposarcoma" of the skin clinically presenting as a skin tag: clinicopathologic, immunohistochemical, and molecular analysis of 2 cases.

Liposarcomas are extremely rare in the skin. When they involve the skin, it is usually by upward spread from a subcutaneous or deeper seated liposarcoma. Very rarely, liposarcoma metastasize to the skin or arise as a primary dermal lesion. We describe 2 cases of atypical lipomatous tumor "well-differentiated liposarcoma" located in dermis. Both presented clinically as a skin tag. The neoplasms arose in a 56-year-old female and a 69-year-old male patient. Both lesions were treated by excision and reexcision. In addition to classical morphology of atypical lipomatous tumor with evidence of lipoblasts and atypical adipocytes, immunohistochemistry with nuclear murine double-minute type 2 protein and cyclin-dependent kinase-4 expression as well as fluorescence in situ hybridization analysis showing an amplification of murine double-minute type 2 protein and cyclin-dependent kinase-4 were helpful to establish the diagnosis. None of the cases recurred after surgical treatment. These 2 cases show the importance of not to misdiagnose lesions which clinically may appear to be benign.