Despite notable advancements in improving patient outcomes in HR+/HER2− BC using CDK4/6 inhibitors, these therapies are associated with several side effects, including neutropenia, cardiac issues, pneumonitis, diarrhea, and elevated levels of alanine aminotransferase (ALT) and/or aspartate aminotransferase [309, 324]. This evidence concerns the gene CDK4 and breast cancer.