The ultrastructure of liposarcoma. A study of 10 cases

An ultrastructural study of 10 liposarcomas is reported. Four of the liposarcomas were wholly or predominantly of well-differentiated, lipoma-like or fibrosing type, 3 of myxoid type, 2 of round cell type and 1 pleomorphic type. The well-differentiated, lipoma-like liposarcomas showed cells with a few, large lipid droplets, few organelles and a peripherally located, fairly large nucleus, The well-differentiated liposarcomas of fibrosing type revealed mostly spindle-shaped, fibroblast-like cells, with abundant rough endoplasmic reticulum and inconspicuous lipid inclusions, surrounded by collagen. One well-differentiated liposarcoma contained an area which was similar to brown adipose tissue and hibernoma. The spindle and stellate shaped cells of the myxoid liposarcomas showed abundant rough endoplasmic reticulum and large smooth-membraned vacuoles filled with moderately dense amorphous material, which appeared to be extruded extracellularly by rupture of the vacuoles. Cytoplasmic lipid droplets were seen in most cells but were much less prominent than in the well-differentiated lipoma-like liposarcomas. Ultrastructurally there were many similarities between the myxoid and round cell liposarcoma, indicating a close relationship between the two types. The pleomorphic liposarcoma revealed cells with one or more large, irregular nuclei, numerous large vacuoles after dissolved lipids, abundant dilated cisternae of rough endoplasmic reticulum and rounded, electron-dense bodies corresponding to PAS-positive hyalin globules seen in the light microscope. The ultrastructural study suggests that the variegated cellular appearance of the different subtypes of liposarcoma reflects the wide cellular spectrum seen during the differentiation of adipose tissue and supports the view that all liposarcomas histogenetically represent a single entity.