Three causes of discrepancies were identified: (1) loss of distinctive histological features resulting in a morphologically undifferentiated tumor (n = 5), even if additional studies confirmed the preservation of diagnostic immunohistochemical markers such as MyoD1 in rhabdomyosarcoma; (2) expansion of a blastic component without preservation of differentiated features (n = 3); (3) true diagnostic errors, mainly in cases in which morphology alone was not sufficient to reach a final diagnosis (n = 4). This evidence concerns the gene MYOD1 and neoplasm.