In the dose escalation part of the phase 1/2a trial testing the first‐in‐class CDK2/4/6i PF‐06873600 (ebvaciclib), an acceptable safety profile was observed along with preliminary evidence of anti‐tumour activity in 59 HR+/HER2−–BC patients who had progressed on a previous CDK4/6i and ≤2 prior chemotherapy lines.78 Here, CDK4 is linked to breast cancer.