In this study, we analyzed multi-omic and clinical data from patients diagnosed with metastatic HR + /HER2- breast cancer who had progressed on a prior CDK4/6 inhibitor, and were treated with a CDK4/6i-containing triplet therapy (palbociclib + everolimus + exemestane) as part of a phase 1b/2 clinical trial. Here, ERBB2 is linked to breast cancer.