We next assessed whether the clinical ATRi, VX-970, could inhibit ARID1A-deficient tumours in vivo. To do this, we generated cohorts of mice with established xenograft tumours derived from either HCT116 ARID1A+/+ or ARID1A−/− cells...We found that, compared with vehicle treatment, VX-970 had no effect on ARID1A+/+ tumours (P=0.45, ANOVA, Fig. 3b) but significantly inhibited the growth of ARID1A−/− tumours (P=0.024, ANOVA, Fig. 3b).