At a median follow-up of 10 months, the median PFS was 2.0 months (95% CI 1.9–2.1), and the median OS was 14 months (95% CI 6.3–21.7), suggesting that tucidinostat plus ET may be an optional sequential strategy for patients with HR+/HER2− advanced BC that has progressed on CDK4/6i. This evidence concerns the gene CDK4 and breast cancer.