Sarcoma sinovial primario de mama

Primary synovial sarcoma of the breast is very rare. We report a case of a 33-year-old woman, who had previously undergone a radical mastectomy, having been diagnosed with fusocellular breast carcinoma. Histopathology revealed a hypercellular lesion formed by spindle cells with storiform and herringbone patterns. Immunohistochemistry showed strong expression of vimentin and CD99, and focal bcl2, EMA, CK AE1-AE3, actin and desmin, with negativity for S100, CD34, CK7, CK14, CK19, hormone receptors, caldesmon and myosin. Molecular biology revealed the expression of the fusion product of the SS18 and SSX genes, indicative of the translocation t(X;18)(p11.2;q11.2), which confirmed the diagnosis of synovial sarcoma.