Notably, CDK4 overexpression was observed in 9.8% of the pretreated ER+/HER2− relapsed breast cancer patients, compared to just 1.5% in the untreated ER+/HER2− metastatic cohort (p = 2.82 × 10−4) and in all three early breast cancer cohorts. Here, CDK4 is linked to breast carcinoma.