ARID1A deficiency is related to a mismatch repair-deficient phenotype with ARID1A mutant tumours showing an increase in TILs, activation of the immune checkpoint and sensitization to the PD-L1 checkpoint blockade in ovarian cancer in in vivo mouse models compared to ARID1A wild-type tumours [18]. The gene discussed is ARID1A; the disease is neoplasm.