An autopsy case of malignant rhabdoid tumor arising from soft parts in the left inguinal region.

An autopsy case of malignant rhabdoid tumor arising from soft parts in the left inguinal region of a 31-year-old Japanese male is reported. The tumor grew rapidly and appeared as a large mass measuring 21.5 X 16.5 cm located in the subcutaneous tissues of the lower abdominal wall. Histologically the tumor was composed of small round cells resembling rhabdomyoblasts, which showed a diffuse or alveolar arrangement. The cytoplasm of the tumor cells was eosinophilic and frequently contained round inclusion bodies, each consisting of an aggregation of globular filaments by electron microscopy. Immunohistochemistry showed the tumor cells to be positive for vimentin and keratin in the cytoplasm, but negative for actin, myoglobin and myosin. At autopsy, extensive metastatic or invasive tumors were observed mainly in the retroperitoneum and pelvic organs. The patient showed hypercalcemia which disappeared for only short periods just after surgery.