Loss of Atrx had no discernable effect on sarcoma growth rates in the absence of treatment, but following a single dose of 20 Gy focal radiation therapy, tumors in P7 KPA mice demonstrated a significant growth delay relative to tumors in the P7 KP mice (Figure 5, A–D, and Supplemental Figure 8, B and C). This evidence concerns the gene ATRX and sarcoma.