ANTINEUROBLASTOMA ANTIBODY NB-84 ALSO IDENTIFIES A SIGNIFICANT SUBSETOF OTHER SMALL BLUE ROUND-CELL TUMORS

NB-84 is a monoclonal antibody to a 57-kDa protein which has previousl y been described as a highly sensitive and specific marker of neurobla stoma. Of the tumors in the differential diagnosis of small blue round cell tumors (SBRCT), such as neuroblastoma, only a small number of Ew ing's sarcoma/primitive neuroectodermal tumors (ES/PNETs) and medullob lastomas have been reported as being positive with monoclonal antibody NB-84; rhabdomyosarcomas, nephroblastomas, and lymphoblastic lymphoma s have been reported as entirely negative. Using sensitive immunocytoc hemical techniques and employing heat-induced epitope retrieval (HIER) , we tested the specificity of NB-84 in a series of 94 SBRCTs. Deparaf finized, formalin-fixed sections were immunostained with antibodies to NB-84 after HIER. NB-84 was positive in 16 of 16 neuroblastomas, 7 of 23 ES/PNETs, 1 of 9 blastemal nephroblastomas, 3 of 13 rhabdomyosarco mas, 10 of 11 medulloblastomas, 1 of 9 esthesioneuroblastomas, and 2 o f 3 small cell osteosarcomas; 8 lymphoblastic lymphomas and 2 mesenchy mal chondrosarcomas were negative. We conclude that, while NB-84 is a highly sensitive marker of neuroblastoma (100%), it may also be positi ve in a significant subset of ES/PNETs (30%). In addition, and in cont rast to previously published reports, we found 23% of rhabdomyosarcoma s and 11% of blastemal nephroblastomas to be NB-84+. We were unable to find reactivity of NB-84 with any cases of mesenchymal chondrosarcoma or lymphoblastic lymphoma. The presence of NB-84 positivity in SBRCTs other than neuroblastoma reinforces the necessity of applying a panel of antibodies in the diagnosis of these tumors.