ERBB2 and breast cancer: The study showed that PFS was significantly prolonged with dalpiciclib plus fulvestrant (15.7 months) versus placebo plus fulvestrant (7.2 months), providing a significant benefit for patients who relapse or progress on previous ET.663 Following these promising results, the efficacy of AI (letrozole or anastrozole) plus dalpiciclib or placebo for endocrine-sensitive HR+/HER2- advanced breast cancer patients was evaluated in the DAWNA-2 trial.