Biphasic axillary synovial sarcoma diagnosed by preoperative fine-needle aspiration cytology

Synovial sarcoma (SS) is a soft-tissue sarcoma which usually occurs in lower extremities. Less than 20 cases of SS located in shoulder or axillary region have been reported, and these studies describe histopathological features. We report a case of axillary SS diagnosed by fine-needle aspiration cytology, immunocytochemistry, and molecular techniques performed on cytology smears. A 48-year-old woman presented with a palpable and well-defined axillary mass which measured 4 cm. On-site smears showed high cellularity with spindle cells, and a mesenchymal tumor was suspected. Definitive cytological analysis showed cells with ovoid- or comma-shaped nuclei arranged in loose sheets and fascicles, associated with naked nuclei and isolated cells. Mitotic count was 2 mitoses/HPF. Immunocytochemical studies showed vimentin and focal CK AE1-AE3 positivity. A PCR was performed and the specific translocation t(X;18) was detected. The lesion was excised and the diagnosis of biphasic SS was confirmed. The identification of SS on cytology specimens is difficult and differential diagnosis is broad. Complementary studies are necessary and they can be performed on FNA smears or cell blocks.