Gene expression of 2534 cancer-related genes from 302 patient tumors revealed that high expression of CCNE1 - but not other genes related to cell cycle regulation (CDK4, CDK6, CCND1, and RB1) - was associated with resistance to palbociclib (median PFS palbociclib arm: 7.6 vs. 14.1 months high vs. low; placebo arm: 4.0 vs. 4.8 months high vs. low). This evidence concerns the gene CDK4 and cancer.