Fig. 2

a The small round cell tumor arranged mainly in a predominantly solid pattern with a vague alveolar pattern noted focally (in the lower right portion of the image). The majority of the tumor cells are primitive in appearance. Occasional tumor cells with more abundant brightly fibrillar eosinophilic cytoplasm, consistent with rhabdomyoblasts (as indicated by arrows) are noted. (Hematoxylin and eosin stain, original magnification ×400). b On immunohistochemistry, the tumor cells are positive for myogenin and indicative of rhabdomyogenic differentiation. (Immunohistochemical staining for myogenin, original magnification ×400). c Typical fusion transcript of PAX3-FOXO1 was detected by reverse transcription polymerase chain reaction, confirming the diagnosis of alveolar rhabdomyosarcoma