Extrauterine Müllerian adenosarcoma of the peritoneum with an extensive rhabdomyosarcomatous element and a marked myxoid change.

A case of extrauterine Müllerian adenosarcoma of the peritoneum in a 20-year-old woman is reported. The tumor was widely based on the abdominopelvic wall and there were no unusual features in the genital organs. The cut surface of the tumor showed a marked gelatinous appearance. The tumor was composed of an admixture of benign Müllerian-type epithelium and sarcomatous stroma. The predominant element of the sarcomatous area was rhabdomyosarcoma, which showed a close resemblance to well-differentiated embryonal rhabdomyosarcoma. In another sarcomatous area, fibroblastic cells without myoblastic properties diffusely proliferated in a marked myxoid background with some collagen bundles. Both the mitotic count and Ki-67 proliferative index of these cells were lower than those of rhabdomyoblastic cells. On follow up, the patient was disease free for 1 year postoperatively, without any subsequent treatment. The present case indicates that extrauterine adenosarcoma can also show histological heterogeneity as do uterine adenosarcomas. The remarkable myxoid change of this tumor seemed to be more largely due to a fibromyxoid element than a rhabdomyosarcomatous element, and the coexistence of the former may be related to the less aggressive behavior of this tumor.