The importance of CDK6 overexpression in mediating resistance to CDK4/6i is further supported by another study in which FAT1 loss-of-function was shown to induce CDK6 overexpression via suppression of the Hippo pathway in tumors of ER+/HER2− breast cancer patients after initiation of CDK4/6i treatment [30]. The gene discussed is ESR1; the disease is breast carcinoma.