Interestingly, in metastatic, drug-relapsed or endocrine-resistant ER-positive breast cancer patients and primary lobular breast cancer patients, who are generally resistant to ER-targeted therapies, ARID1A inactivating mutations are more frequently observed, suggesting that ARID1A loss is sufficient to mediate therapy resistance (Desmedt et al., 2016; Yates et al., 2017; Razavi et al., 2018; Nagarajan et al., 2020; Xu et al., 2020; Schwartz et al., 2021). This evidence concerns the gene ARID1A and Hereditary breast cancer.