Extraskeletal neoplasm resembling Ewing's sarcoma.

This article reviews the pathologic features and the behavior of 39 small, round, or oval cell sarcomas occurring in the soft tissues and considered histologically indistinguishable from Ewing's sarcoma of bone. The tumors affected chiefly young adults (median age 20 years) and most commonly involved the soft tissues of the lower extremity and the paravertebral region. Microscopically, they consisted of solidly packed small, round, or ovoid cells of great uniformity, arranged in sheets or lobules separated by strands of fibrous connective tissue. The nucleus of the tumor cells contained finely divided chromatin, a distinct nuclear membrane, and frequently a minute nucleolus. The scanty ill-defined cytoplasm contained varying amounts of glycogen. Sometimes the histologic picture was dominated by a "peritheliomatous" pattern, or by large areas of necrosis or hemorrhage. Followup data ranging from 1 month to 14 years were available in 35 of the 39 cases (93%). Of these, 13 were alive and 22 had died. In the majority of the fatal cases, the clinical course was rapid; metastatic lesions developed within a few months after the primary tumor was excised. The lungs and the skeleton were the two most common sites of metastasis. Cure may be achieved by wide local excision of the tumor at an early stage of the disease, combined with radiation therapy and chemotherapy.