<h4>Patients and methods</h4>we retrospectively collected data of patients with HR+/HER2- advanced breast cancer (ABC) treated with endocrine therapy (ET) and a CDK4/6 inhibitor (CDK4/6i) aiming to describe the patterns of post-progression outcomes.<h4>Results</h4>Among 452 evaluable patients 325 were treated in the first-line setting. The gene discussed is ERBB2; the disease is breast cancer.