Epithelioid sarcoma with heterotopic bone: a morphologic review of 4 cases.

Epithelioid sarcoma is an uncommon malignancy that usually arises in the superficial soft tissues of the extremities. Classically, epithelioid sarcoma grows as nodules of mild to moderately atypical epithelioid cells, frequently with central necrosis. The stroma is variably fibrous and may rarely contain heterotopic bone. The presence of bone within epithelioid sarcoma raises a variety of lesions in the differential diagnosis, including reactive processes as well as benign and malignant neoplasms.This morphological variant of epithelioid sarcoma and its associated diagnostic pitfalls has received little attention in the literature. The authors report herein 4 cases of epithelioid sarcoma with heterotopic bone and highlight the morphological characteristics of the bone and how such variants can be distinguished from other bone-forming lesions of the soft tissues.