Rhabdomyosarcomas are a heterogeneous group of malignant tumors showing skeletal muscle differentiation. They can be divided into 3 subtypes: alveolar, embryonal, and pleomorphic. The rarer alveolar rhabdomyosarcomas (ARMS) are seen in older children, are more likely to occur in limbs, and are associated with higher stage disease and an unfavorable prognosis.
Chromosomal rearrangements involving the FOXO1 gene on chromosome 13q14 are associated with alveolar rhabdomyosarcoma (ARMS). Identification of RMS is a diagnostic dilemma for pathologists, requiring a significant amount of rule out testing for this and other soft-tissue cancers. Most cases of ARMS (75%) are associated with a t(2;13)(q35;q14), where a chimeric gene is formed from the rearrangement of the PAX3 gene on chromosome 3 and the FOXO1 (FKHR) gene on chromosome 13. A small subset of ARMS patients (10%) are associated with a variant translocation, t(1;13)(q36;q14), involving the PAX7 gene on chromosome 1 and the FOXO1 gene.
A positive result suggests rearrangement of the FOXO1 gene region at 13q14 and is consistent with a subset of alveolar rhabdomyosarcomas (ARMS). Correct identification allows to select an appropriate therapy.