Myxoid liposarcoma: study of ten cases.

The ultrastructure of 10 myxoid liposarcomas from 9 patients is presented. Features closely resembling those of developing fetal adipose tissue were seen in all tumors. THe various cell types identified ranged from undifferentiated cells to typical multivacuolated and univacuolated lipoblasts. In addition, a secretory type mesenchymal cell with distended cisternae of rough endoplasmic reticulum was found in every case as well as intermediate cells with secretory product and lipid accumulation. relative proportions of these types varied from case to case. A prominent feature in all cases was the particular spatial relationship of the abundant capillaries to the various cell types. The undifferentiated cells had perivascular processes with a tendency to envelop the primitive capillaries. These cells progressively enlarged and acquired features of the differentiated cell types as they separated from the lamina. Mitotic activity, when detectable, was prominent in the capillary wall and its vicinity. Lipoblasts resembling those of brown adipose tissue frequently coexisted in the same tumor with others analogous to those of white adipose tissue. Our findings suggest that tumor cells in liposarcoma originate from a dividing population of perivascular mesenchymal cells, in a manner akin to that of developing white adipose tissue.