In a related report of non-aRMS soft tissue sarcomas, Rb1 loss accelerated progression of p53-initiated tumors and led to undifferentiated phenotypes, but, as expected, did not induce tumor initiation in a conditional model using a Prx-cre driver (specific to the mesenchymal tissue of the limb bud) [34]. The gene discussed is PRX; the disease is soft tissue sarcoma.