Gene Amplification in Rhabdomyosarcoma: Lessons from a Rare Cancer

Studies of the pediatric soft tissue cancer alveolar rhabdomyosarcoma have contributed to the current understanding of the diverse set of molecular changes that occur as part of the gene amplification process. In accord with the traditional view of amplification, the amplicon from the 2p24 chromosomal region primarily involves a single protein-coding gene (MYCN). In contrast, amplification of the 12q13-q14 chromosomal region involves a gene-rich region in which there are at least two critical protein-coding oncogenic targets (CDK4 and SHMT2). Amplicons involving the 1p36 and 13q14 chromosomal regions co-occur as part of a multistep process in which a mutation, in this case a translocation that forms a gene fusion (PAX7::FOXO1), is followed by amplification. Analysis of the amplicon involving the 13q31 region highlights an example of a situation in which the critical amplification target is a gene for a non-coding RNA (MIR17HG) instead of a protein-coding gene. Translational studies of the prognostic significance of these amplicons emphasize important considerations encountered in defining useful prognostic markers. Finally, preclinical investigations revealed that some amplification events (CDK4 and SHMT2) decrease susceptibility to drugs that directly target the amplified gene products and increase susceptibility to drugs targeting proteins that function in signaling pathways downstream of these amplified gene products. These combined studies in alveolar rhabdomyosarcoma emphasize the biological and clinical complexities of gene amplification in cancer.