ARID1A and neoplasm: Consistent with our previous observations, for eRAS/BRAF WT PDX tumors, ARID1A mutant-like tumors were less responsive to cetuximab than the ARID1A WT-like group as evidenced by a greater tumor volume increase observed at 3 weeks post-treatment (Wilcoxon rank sum p < 0.01, Fig. 3c), as well as by a lower fraction of responder cases (PR, SD-PR) in the ARID1A mutant-like group compared to the ARID1A WT-like group (Fisher exact p = 0.05, ORR = 11% vs. 36%, respectively, Fig. 3d).