FOXO1 and alveolar rhabdomyosarcoma: ERMS and ARMS are the most prevalent, accounting for 70 and 20% of RMS cases, respectively.1 Most ARMS tumors express fusion proteins combining the DNA-binding domain of either PAX3 or PAX7 transcription factors with the transcriptional-activation domain of FOXO1A.2, 3 ERMS accounts for most RMS cases, although its molecular basis remains poorly understood.