Variability of histologic pattern in recurrent soft tissue sarcomas originally diagnosed as liposarcoma.

The histopathologic classification of liposarcoma and its clinicopathologic significance are well delineated in previous studies, but the literature is inexplicably mute on recurrent liposarcomas. Supposition and experience may have led to the assumption that the microscopic features remained static over a period of years and multiple recurrences. Thirteen sarcomas originally classified as liposarcoma were reviewed to assess patterns of histologic change with recurrence. A total of 52 recurrences was studied. In 7 of the 13 cases, multiple morphologic sarcomatous patterns were identified, either as a change with recurrence or as multiple discrete patterns within a tumor. All changes except in one case occurred before irradiation or chemotherapy. The variations included patterns such as malignant fibrous histiocytoma, hemangiopericytoma, malignant schwannoma, and unclassified spindle-cell sarcoma as well as the various liposarcoma subtypes. This variability of patterns can cause significant diagnostic difficulties and can cause one to question the validity of using monomorphic diagnoses in all cases. In addition, the polymorphic differentiation of these tumors supports the concept that soft tissue sarcomas are derived from a pluripotential mesenchymal stem cell.