PAX3 and alveolar rhabdomyosarcoma: The two major subtypes are the alveolar (ARMS), more frequently expressing the pro-oncogenic fusion proteins PAX3/7-FOXO1 (PAX3/7-FKHR), namely “fusion positive” RMS (FP-RMS), and the embryonal (ERMS), characterized by different mutations, “fusion negative” (FN-RMS).