Findings for the PALOMA-1 trial23 resulted in approval for Palbociclib (CDK4/6 inhibitor) in combination with Letrozole in the metatstatic breast cancer setting; paving the way for the randomization of high-risk patients with ER+/HER2-cancer and residual disease, in the PENELOPE-B trial. This evidence concerns the gene ERBB2 and breast cancer.