The Role of Immunohistochemistry in Rhabdomyosarcoma Diagnosis Using Tissue Microarray Technology and a Xenograft Model.

Rhabdomyosarcomas (RMS) may resemble other non-myogenic sarcomas and malignant rhabdoid tumor (MRT). Alveolar rhabdomyosarcoma (ARMS) often harbors a typical translocation, but embryonal rhabdomyosarcoma (ERMS) lacks any specific rearrangement. Histopathology is not always sufficient for an unequivocal diagnosis, necessitating ancillary studies, including immunohistochemistry (IHC). Sixteen genetically tested RMS and two MRT were xenografted and followed in successive passages. Tissue microarrays were constructed including samples from original and xenograft tumors. Desmin, myogenin, CK, EMA, INI1, LSD1, AP2β, fibrillin-2, HMGA2, nestin, and SIRT1 were tested using immunohistochemical staining. Desmin and myogenin were positive in all RMS, and the epithelial markers were negative in almost all RMS. New markers (LSD1, AP2β, HMGA2, Nestin, and SIRT1) were positive in all RMS and MRT. There were no differences in IHC expression between the three RMS subtypes tested except fibrillin-2, which was negative in ARMS. Applying new IHC markers can contribute to RMS diagnosis. Nevertheless, most markers are also expressed in MRT, and further studies are needed to confirm their value against this and other small round cell tumors.