The combination of CDK4/6 inhibitor abemaciclib and HER2 inhibitor tucatinib resulted in significant tumor regression in p16INK4A-negative, HER2-positive BC BM patient-derived xenograft models compared with either drug alone23, suggesting that patients with HER2-positive BC and BM may benefit from the combination treatment. This evidence concerns the gene CDKN2A and breast cancer.