Rhabdomyosarcoma: molecular diagnostics of patients classified by morphology and immunohistochemistry with emphasis on bone marrow and purged peripheral blood progenitor cells involvement

Two histologically distinct subtypes of rhabdomyosarcomas (RMS), embryonal and alveolar, are different in many aspects, such as age distribution, primary site, and clinical outcome. We analyzed a group of 30 patients with RMS. The aim was to broaden the spectrum of diagnostic tools in evaluating the primary tumors, their recurrences and/or metastases, and to extend the diagnostic boundary to bone marrow and purged peripheral progenitor blood cell samples. We have performed the RT-PCR assay to analyze RMS for the presence of expression of MyoD1 gene and for the presence of chimeric transcripts PAX3/FKHR or PAX7/FKHR. MyoD1 gene expression was found in all 30 patients in samples from primary tumors. The chimeric transcripts PAX/FKHR were identified in 13 of 15 patients with alveolar RMS. Furthermore, the fusion transcript PAX7/FKHR was identified in 2 of 15 patients with RMS classified as embryonal by histology. Bone marrow samples (12) and peripheral blood progenitor cell specimens (13) in ten patients were examined by RT-PCR. We were able to identify 7 patients with bone marrow involvement and/or with contamination of peripheral blood progenitor cells by the tumor cells. We demonstrate that employing molecular diagnostics has an impact on staging, therapy monitoring and recognition of malignant cells at the tumor resection margins.