Liposarcomas. A histogenetic approach to the classification of adipose tissue neoplasms.

A series of atypical lipomas, well-differentiated/dedifferentiated liposarcomas, and myxoid/round cell liposarcomas were examined by light and electron microscopy in order to understand better the marked variation in histologic growth patterns exhibited by adipose tissue neoplasms. We found that they were composed of a mixture of adipocytes and nonfat-storing mesenchymal cells or were predominantly made up of only one of these cell types. From these and other published observations, we feel that 1) myxoid/round cell liposarcomas are composed of adipocytes; 2) spindle cell lipomas, atypical lipomas, and well-differentiated liposarcomas are composed of a mixture of the two cell types; and 3) the dedifferentiated regions of well-differentiated liposarcomas are composed of nonfat-storing mesenchymal cells. The basic structural differences of the two cell types and the quantitative variations when they occur in mixtures seem to account for the marked variations in neoplastic growth patterns.