Currently, three CDK4/6i are approved for advanced HR+HER2− BC treatment—palbociclib, ribociclib and abemaciclib [23,24,25], now being studied in other BC subtypes, including HR+/HER2+ (e.g., NCT03709082; NCT03913234; NCT02448420), HER2+ (e.g., NCT04351230; NCT02448420) and triple-negative BC (TNBC) (e.g., NCT05067530; NCT03130439). This evidence concerns the gene CDK4 and breast cancer.