Transcriptomic Predictors of Survival for Palbociclib + Endocrine Therapy Versus Capecitabine in Aromatase Inhibitor–Resistant Breast Cancer From the GEICAM/2013-02 PEARL Trial

PAM50 intrinsic subtype predicted PFS differences between palbociclib + ET and capecitabine. Lower B-cell-associated gene expression predicted longer OS with palbociclib + ET versus capecitabine. These features may help identify HR+/HER2- tumors resistant to further ET-based treatment with CDK4/6i.