The frequency of PAX3 and PAX7 Mutations in Children with Rhabdomyosarcoma

Abstract Background: Rhabdomyosarcoma is the most common soft tissue sarcoma among children which has two major subtypes: embryonal rhabdomyosarcoma (ERMS) and alveolar rhabdomyosarcoma (ARMS). Distinction between these subtypes is mandatory to choose proper treatment and to determine prognosis. Histopathologic study is the main method, but nowadays molecular studies like PCR are also used. The aim of this study was to evaluate the frequency of PAX3 and PAX7 mutations in children with rhabdomyosarcoma. Materials and Methods: In this cross- sectional survey, Paraffin blocks of 34 Rhabdomyosarcoma cases with mean age of 6.3 ± 2.9 years  were studied in Mofid Children's Hospital's Pathology Department, Tehran, Iran, during a 10-year period. Tumoral lesions dissected and embedded in paraffin blocks for PCR study (Tissue dissection method). Pure RNA extraction, cDNA synthesis, and PCR process were performed according to iNtRON biotechnology company kits’ protocols. All of these cases were analyzed regardingPAX3 and PAX7 mutations. Results: Out of 34 cases, 32 were ERMS and two were ARMS. None of the ERMS samples was t (2; 13) or t (1; 13) positive. Moreover, two ARMS cases were negative for PAX3 and PAX7 mutations. No significant difference was seen for age below and above five years (P= 0.69) as well as for tumor location (trunk tumor and limbs/head tumor) (P= 0.11). Conclusions: This study revealed lack of PAX3 and/or PAX7 mutations in both ERMS and ARMS. However, careful morphological evaluation cannot be replaced by the PCR-based t(2;13) and t(1;13) assay  of  childhood sarcomas,  it can  be  used  to  make certain current histopathological diagnosis.