Immunohistochemical evaluation of ERG expression in soft tissue tumours: a tissue microarray study of 489 cases

Aims To investigate immunohistochemical expression of the E26 transformation-specific factors (ETS)-related gene ( ERG ) in a large number of soft tissue neoplasms using a tissue microarray technique. Methods 489 cases of soft tissue neoplasms, including benign and malignant entities, were collected from the files of the respective institutions and constructed into tissue microarrays. Tissue microarrays were stained for ERG immunohistochemistry using two antibodies, EP111 and EPR3864. Results A total of 25 cases (5.1%) were identified that were positive for ERG using the monoclonal antibody EP111 and 15 cases (3%) using the monoclonal antibody EPR3864, including rhabdomyosarcoma, peripheral nerve sheath tumours, synovial sarcoma, myxofibrosarcoma, epithelioid sarcoma, dermatofibrosarcoma protuberans, low-grade fibromyxoid sarcoma, nodular fasciitis and dedifferentiated liposarcoma. The most consistently stained tumours included synovial sarcoma, rhabdomyosarcoma and benign and malignant peripheral nerve sheath tumours. Various other fibroblastic proliferations, including dermatofibrosarcoma protuberans, myxofibrosarcoma, low-grade fibromyxoid sarcoma and nodular fasciitis, also showed positive staining in a small fraction of cases. One case of dedifferentiated liposarcoma showed nuclear positivity for ERG, and one case of epithelioid sarcoma was also positive. Conclusions This study supports the value of ERG as a highly sensitive and specific marker for the diagnosis of vascular neoplasms but also demonstrates rare cases of aberrant staining and underscores the need to assess soft tissue tumours using a panel of stains and interpret the results of immunohistochemistry in the appropriate histological and clinical context.