Molecular Cytogenetics Detect an Unbalanced t(2;13)(q36;q14) and PAX3-FOXO1 Fusion in Rhabdomyosarcoma With Mixed Embryonal/Alveolar Features.

Distinguishing between alveolar rhabdomyosarcoma (ARMS) and embryonal rhabdomyosarcoma (ERMS) is crucial because treatment and prognosis are different. We describe a case of paratesticular rhabdomyosarcoma (RMS), which was classified as mixed ERMS/ARMS. Fluorescence in situ hybridization (FISH) detected losses of 3'PAX3 and 5'FOXO1, suggesting they had undergone an unbalanced rearrangement that probably produced the PAX3-FOXO1 fusion. Double-color FISH and reverse transcription-polymerase chain reaction (RT-PCR) revealed PAX3-FOXO1, which is characteristic of high-risk RMS. This finding highlights the importance of supplementing histology with genetics so that atypical RMS is appropriately classified and patients are correctly stratified and treated.