Soft tissue sarcoma with complex membranous and microtubular inclusions.

Cytoplasmic inclusions of great complexity are encountered in an undifferentiated sarcoma of a 67-year-old woman. The tumor arising in adipose tissue between muscles of the parspinous musculature contains inclusions in most tumor cells represented by four different morphologic types. Two are intracisternal, designated microtubular reticular structure (TRS) and tubular confronting cisternae (TCC). Two others are cytoplasmic and consist of crystalline microtubular arrays and of confronting cisternal complexes of smooth endoplasmic reticulum (SER). This latter is uniquely complex and not found in previous descriptions. Tumors of mesenchymal origin and experimental virus-induced tumors are known to contain short segments of confronting cisternae and TRS. Tubuloreticular structures and TCC are well documented in cases of lupus, in human immunodeficiency virus infections, in T-cell leukemia, and in experimental viral hepatitis in chimpanzees. The patient presented has none of the coincidental pathologic condition associated with occurrence of TRS and TCC. The morphology of the inclusions and their relationships are illustrated although their biological significance remains obscure.