Synovial sarcoma, which has a wide spectrum of
biologic behavior, warrants accurate grading to assess the patient's prognosis. We studied the clinicopathologic and immunohistochemical features of 44 cases of
synovial sarcoma in patients treated primarily or secondarily at the National
Cancer Center, Tokyo, to identify independent prognostic factors. There were local recurrences in 16 patients (36%), and 25 (57%) developed
metastases, primarily to the lungs. The estimated cumulative 5-year and 10-year survival rates were 68% and 41%, respectively. Variables associated with an adverse outcome included
tumor size > 6.7 cm; initial treatment outside the National
Cancer Center; poorly differentiated subtype; high nuclear atypia; mitosis count > 27/10 high-power fields;
tumor necrosis; absence of stromal calcification; nuclear expression of
beta-catenin, which was found in 25 cases (57%); Ki-67 (MIB-1) index > 27%; and histologic grade 3. Nuclear accumulation of
beta-catenin as a cell-signaling event may play an important role in the progression of
synovial sarcoma and therefore might be predictive of short survival. However, multivariate analysis clearly showed that only histologic grade, as defined by using categorized variables for the MIB-1 index and
tumor necrosis, was an independent prognostic factor. Most variables were correlated with lung
metastasis and histologic grade. High-grade
synovial sarcoma assessed by a histologic grading system based on the proliferative activity of the neoplastic cells can be viewed as high risk with the patients most likely to die of disease within 10 years after surgery and in need of improved
chemotherapy. HUM PATHOL 32:257-263.