Rosette-forming epithelioid osteosarcoma: a histologic subtype with highly aggressive clinical behavior

Osteosarcoma shows a variety of histologic patterns. Rarely, this tumor may appear epithelioid, including a rosettelike configuration simulating glands. We retrospectively reviewed 16 cases of osteosarcoma with rosettelike structures treated at the National Cancer Center and Akita University, Japan, from 1972 to 1999. The 16 patients were under 30 years of age, and males were predominant in the sex distribution. The tumors arose primarily in the metaphysis of long tubular bones, and the most common symptom was pain. Roentgenographically, the lesions showed a highly destructive appearance with varying degrees of mineralization. Twelve patients (75%) died of multiple lung metastases in spite of surgery with wide surgical margins and systemic chemotherapy. The estimated cumulative 5-year survival rate was 15%, significantly worse than the rate of 55% in 70 cases of conventional osteoblastic osteosarcoma without rosettelike structures arising in long tubular bones. All of the 16 tumors, originally classified as conventional osteoblastic osteosarcoma, predominantly displayed a small multinodular growth pattern with lacelike osteoid deposits in the center between dilated blood vessels showing a hemangiopericytoma-like appearance. Ten tumors (63%) showed immunoreactivity for epithelial membrane antigen. We believe rosette formation in osteosarcomas of long tubular bones is an ominous sign; therefore, those tumors should be distinguished from osteosarcomas with conventional morphotypes.