Monophasic and biphasic synovial sarcomas abundantly express cancer/testis antigen ny-eso-1 but not mage-a1 or ct7

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Abstract
Synovial sarcomas are high‐grade malignant mesenchymal tumors with biphasic (BSS) and monophasic (MSS) variants that carry a pathognomonic cytogenetic alteration, t(X;18), involving the SYT gene on chromosome 18 and one of several SSX genes on chromosome X, usually SSX1 or SSX2. Cancer/testis (CT) antigens are expressed in a variety of malignant neoplasms but, in normal tissues, are restricted to male germ cells. Previous analysis revealed a high incidence and homogeneous expression of MAGE CT antigen in synovial sarcomas. The present study was performed to analyze the expression of 3 CT antigens, NY‐ESO‐1, MAGE‐A1 and CT7, by immunohistochemistry with 3 monoclonal antibodies (MAbs), ES121 (anti‐NY‐ESO‐1), MA454 (anti‐MAGE‐A1) and CT7‐33 (anti‐CT7), in 25 synovial sarcomas (12 MSS, 13 BSS) typed for the t(X;18)‐derived fusion transcript by RT‐PCR (19 SYT‐SSX1, 6 SYT‐SSX2). NY‐ESO‐1 immunoreactivity was found in 20/25 (80%) cases, and antigen expression was homogeneous in 14/20 NY‐ESO‐1‐positive cases. Both morphologic variants and both translocation types were NY‐ESO‐1‐positive, whereas 5 SYT‐SSX1 tumors (1 MSS, 4 BSS) were NY‐ESO‐1‐negative. MAb MA454 was immunoreactive with 4/25 cases (2 MSS, 2 BSS; 3 SYT‐SSX1, 1 SYT‐SSX2), and MAb CT7‐33 was immunoreactive with only 2/25 cases (both BSS, SYT‐SSX1). Expression of MAGE‐A1 and CT7 was heterogeneous in all positive cases. Our study shows that NY‐ESO‐1 is highly expressed in a homogeneous pattern in synovial sarcomas of both morphologic variants and both translocation types, making these tumors an attractive target for NY‐ESO‐1 antigen‐based immunotherapy.