Primary round cell liposarcoma of the omentum. A case report.

Liposarcomas are the most common of the malignant soft tissue tumors arising in the mediastinum and retroperitoneum. We have treated patients for round cell liposarcoma, an unusual histologic subtype, which is reported to be histologically mistaken for Ewing's sarcoma, lymphoma and other round cell neoplasms. The successful resection of a 2,300-g round cell liposarcoma of the omentum was recently performed at our hospital. Ultrastructural observations of this tumor are characterized by massive proliferation of the mitochondria in addition to the presence of lipid vacuoles in tumor cells. To our knowledge, no description of substantial mitochondrial proliferation in round cell liposarcoma has appeared previously in the literature; therefore, this is the first case report of histopathologic, cytopathologic and electron microscopic observations on this extremely rare tumor.