Results of a prospective minimal disseminated disease study in human rhabdomyosarcoma using three different molecular...

Rhabdomyosarcoma (RMS) has 2 major histologic subtypes: alveolar (ARMS) and embryonal (ERMS). ARMS is more aggressive and prone to distant tumor dissemination, whereas ERMS tends to expand and recur locally. Little information is available on bone marrow involvement by RMS.

We determined the sensitivity and specificity of MyoD1, myogenin, and PAX-FKHR transcripts as RMS markers and used them to study prospectively by reverse-transcriptase polymerase chain reaction (RT-PCR) a series of consecutive unselected RMS patients enrolled in the Italian Association of Pediatric Hematology and Oncology national trial. Prevalence of minimal disseminated disease (MDD) and its response kinetics to chemotherapy were assessed.

MyoD1 and myogenin were specifically associated with RMS, independently of histologic subtype, whereas PAX3/7-FKHR transcripts were expressed only in ARMS. Sensitivity was higher for MyoD1 compared with myogenin and PAX-FKHR. Out of a cohort of 40 patients, MDD positivity was limited to ARMS, with the sole exception of 1 ERMS. Prevalence of MDD positivity increased when a real-time polymerase chain reaction approach was used on a subgroup of patients. RT-PCR was more sensitive than microscopic examination of bone marrow biopsies. The study of the response kinetics of MDD showed that in approximately half of the cases, bone marrow was cleared of disease after 1 cycle of chemotherapy.

MyoD1 and myogenin transcripts can be used as tumor markers for MDD assessment in virtually all RMS cases, whereas PAX-FKHR is specific for ARMS. Sensitivity of RT-PCR methods was superior compared with standard morphologic assays. Our study suggests that bone marrow involvement is more common in ARMS compared with ERMS, and that MDD can be often cleared by the initial chemotherapy cycles.