Synovial sarcoma of the extremities: a clinicopathologic study of 34 cases, including semi-quantitative analysis of spindled, epithelial, and poorly differentiated areas.

Many clinicopathologic studies of synovial sarcoma have grouped together tumors from different sites. The goal of this study was to identify clinical and pathologic features that correlate with a poor outcome in patients with extremity synovial sarcoma. Thirty-four cases of synovial sarcoma of the extremities were studied. Inclusion criteria included a consistent histology, the immunohistochemical expression of at least one epithelial marker (AE1/3, CAM 5.2, or epithelial membrane antigen), and adequate clinical follow-up. Features evaluated included the presence and extent of spindled, epithelial, and poorly differentiated areas, the presence and extent of calcification and necrosis, nuclear grade, the presence or absence of cells with a rhabdoid morphology, and the number of mitotic figures (MFs) per 10 high power fields (HPFs). Patients were considered to have an adverse outcome if they developed metastatic disease or died from tumor. The cohort included 15 males and 19 females with a median age 36 years (range, 11-82 years). There were 22 lower extremity tumors and 12 located on the upper extremities. Tumor size ranged from 1.2 to 16 cm (median, 6 cm). Follow-up ranged from 9 to 108 months (median, 38 months). Eleven (32%) patients had an adverse outcome, all with metastatic disease. Features associated with an adverse outcome included increasing age (p = 0.04), tumor size of 5 cm or greater (p = 0.03), tumor location on the lower extremities (p = 0.04), the presence of poorly differentiated areas (p = 0.04), grade 3 nuclei (p = 0.005), cells with a rhabdoid morphology (p = 0.003), and more than 10 MFs/10 HPFs (p = 0.005). Patients whose tumors were composed of at least 20% poorly differentiated areas were significantly more likely to have an adverse outcome (p < 0.001). In conclusion, a variety of clinical and pathologic features are associated with an adverse outcome in patients with synovial sarcoma of the extremities. These features include increasing age, tumor size of 5 cm or more, lower extremity tumor location, the presence of poorly differentiated areas, particularly when at least 20% of the tumor, grade 3 nuclei, rhabdoid cells, and more than 10 MFs/10 HPFs.