Immunohistochemistry of small round blue cell tumors of childhood

Small round blue cell tumors in childhood represent a diagnostic category o f tumors that show no distinguishing morphologic features but require accur ate identification because of their requirement for specific therapies and different clinical outcomes. While the use of ancillary investigations such as cell culture, cytogenetics, and molecular analysis has contributed to t heir identification and our understanding of their pathogenesis, electron m icroscopy and immunohistology have proven to be the most practical diagnost ic tool in this category of tumors. In the majority of cases, a carefully s elected panel of antibodies allows the identification of rhabdomyosarcoma, leukemia/lymphoma, neuroblastoma, Ewing's sarcoma/peripheral neuroepithelia l tumors, desmoplastic small round cell tumor, and mesenchymal chondrosarco ma. Although no single antibody is specific, the combination of a number of positive and negative markers produces an immunohistochemical profile that is relatively specific to each of these tumors. To aid understanding of th e immunophenotype and histogenesis, molecular aspects of each lesion is bri efly discussed.