Synovial sarcoma--identification of favorable and unfavorable histologic types: a Scandinavian sarcoma group study of 104 cases.

Synovial sarcoma has traditionally been regarded as a high-grade sarcoma and treated as such. Recently, specific types of poorly differentiated synovial sarcoma have been defined and shown to affect prognosis adversely. We studied 104 primary synovial sarcomas of the extremities and trunk wall without metastasis at diagnosis that were retrieved from the Scandinavian Sarcoma Group Registry (SSG) and the Swedish Cancer Registry from 1986 to 1994. Follow-up was available in all patients, median 6 (3-11) years for the survivors. There were local recurrences in 15% of patients and metastases in 33%. Histologically, the tumors were divided into favorable and unfavorable types. The favorable type had no significant cytologic atypia, and in most instances, no necrosis and a mitotic count of < 10/10 hpf. The unfavorable type included so-called poorly differentiated synovial sarcomas as well as recognizable biphasic and monophasic synovial sarcomas with prominent nuclear atypia, extreme cellularity and nuclear crowding. Designation of a tumor as having favorable vs. unfavorable histology conveyed more prognostic information than any single histologic factor. Kaplan-Meier estimates of metastasis-free survival at 5 years were 83% for patients with histologically favorable tumors and 31% for patients with histologically unfavorable tumors (95% confidence intervals 72-92% and 13-51%, respectively). These findings may influence future treatment protocols for synovial sarcoma.