CCR2 and neoplasm: We observed significantly enhanced tumor regression of MC38 tumors grown in CCR2−/− hosts treated by local IR as compared with tumors grown in wild-type (WT) mice (Fig. 2a, Day 31, CCR2−/− IR 52 ± 33 vs. WT IR 351 ± 82, P < 0.05: Student’s t-test).