[Diagnosis of micrometastases of alveolar rhabdomyosarcoma]

Alveolar rhabgomyosarcoma is a highly malignant, small blue cell pediatric soft tissue tumor. Identification of micrometastases in alveolar rhabdomyosarcoma is important because the poor prognosis associated with this subgroup necessitates a modified therapeutic regimen. Since the obtained lymph node specimen can be very small; rhabdomyosarcoma cells are not easily detected using conventional histological methods. To assess the value of myogenin staining in the diagnosis of micrometastases in alveolar rhabdomyosarcoma, the authors examined 36 lymph nodes from children bearing this tumor. Occult tumor cells were detected in 8 cases. The PAX3/7-FKHR gene fusion that resulted from chromosomal translocation in alveolar rhabdomyosarcoma provided potential molecular diagnostic markers. Reverse-transcriptase polymerase chain reaction (RT-PCR) was used to develop an assay capable of identifying RAX3/7-FKHR positive cells in the fresh lymph nodes. Thirty-six lymph nodes were examined and of them 17 lymph nodes had PAX3/7-FKHR fusion transcripts of alveolar rhadomyosarcoma cells. The study demonstrates that molecular RT-PCR detection of micrometastases is the most sensitive method for diagnosing alveolar rhabdomyosarcoma.