Pleomorphic lipoma: a benign tumor simulating liposarcoma. A clinicopathologic analysis of 48 cases.

A clinicopathologic study of 48 cases of pleomorphic lipoma from the files of the Armed Forces Institute of Pathology reveals that this tumor occurs principally in males (83%) in the fifth to seventh decades (mean 57 years) and shows a predilection for the posterior neck, shoulder, and back. Typically, the lesion appears as a painless, circumscribed subcutaneous mass that, on gross examination, resembles an ordinary lipoma. However, microscopically, in contrast to the uniform appearance of the mature adipose tissue cells of an ordinary lipoma, this neoplasm is characterized by an intimate admixture of variably-sized fat cells, and bizarre, pleomorphic, multinucleated giant cells. Many of the latter cells show a distinctive floret-like arrangement of the nuclei and are associated with interlacing bundles of dense birefringent collagen. Despite this pleomorphic picture, which not infrequently leads to a misdiagnosis of liposarcoma, follow-up data obtained for 34 patients (median follow-up period of three years) establish the invariably benign clinical behavior of this unusual tumor.