PAX-7 (BSB-145), MMab

Summary and Explanation

PAX-7 is restricted to muscle satellite and myogenic precursor cells in adults, although it is upregulated in embryonal (ERMS) and alveolar rhabdomyosarcoma (ARMS) and could suggest a de-differentiated cell type when overexpressed in these tumors. Recent studies suggested that PAX-7 antibody is a novel marker, because it was expressed consistently in Ewing sarcoma, in addition to rhabdomyosarcoma and synovial sarcoma. PAX-7 antibody was found expressed in 90% of Ewing sarcomas (90%), mainly in a diffuse and strong manner. Although NKX2-2 showed similar sensitivity, PAX-7 showed more extensive and strong reactivity. ARMS differs from ERMS by virtue of its occurrence in older patients, distinctive pseudoalveolar pattern, usual absence of strap cells, and strong myogenin rather than MyoD1 expression. Identification of a PAX3 or PAX-7/FKHR fusion gene may be necessary for the confident distinction of ARMS from the most primitive forms of ERMS.