FOXO1 and neoplasm: Histologically, Pax3:Foxo1a,Rb1 tumors consisted of myogenin and desmin-positive small round blue cells, consistent with the diagnosis of aRMS, whereas Rb1 tumors were represented as mixed spindle and small round blue cells with only focal regions of myogenin or desmin positivity consistent with either RMS not otherwise specified or poorly differentiated malignant epithelioid neoplasms (Figure 4).