Fine-needle aspiration biopsy of synovial sarcoma. A cytomorphologic analysis of primary, recurrent, and metastatic tumors.

Thirteen fine-needle aspiration specimens from 10 patients with histologically proven synovial sarcoma are described. The aspiration biopsy specimens were obtained from the primary tumor in five cases, locally recurrent tumors in four cases, pulmonary metastases in three cases, and mediastinal metastasis in one case. Patient's ages ranged from 22 years to 65 years; there were four women and six men. All cases had a confirmation biopsy and/or resection specimen that were reviewed. Histologic subtypes included monophasic fibrous (5 cases), monophasic epithelial (1 case), biphasic (3 cases), and poorly differentiated (1 case). The majority of the aspiration biopsy specimens were similar with moderate to marked smear cellularity dominated by cohesive clusters of spindle-shaped cells with ovoid, hyperchromatic nuclei and scanty tapering cytoplasm. Nucleoli were not prominent. Epithelial tumor cells with ovoid to round, mostly regular, centrally to eccentrically located nuclei, surrounded by scant to abundant cytoplasm predominated in one case (monophasic epithelial) and were admixed with spindle cells in a second (classical biphasic). Multi-nucleated tumor giant cells were not observed in any of the tumors. In biphasic synovial sarcoma, the neoplastic spindle cells are generally more numerous and frequent than the epithelial cells, making distinction from monophasic synovial sarcoma or other spindle cell soft tissue tumors difficult. Although synovial sarcoma may be diagnosed by fine-needle aspiration cytology, clinical correlation, especially in monophasic types, is necessary to minimize errors in sarcoma classification.