In addition, the benefit of palbociclib for the HER2-E subtype demonstrated in the PALOMA-2 and PALLET cohorts in this study and in the PALOMA-2 cohort by Finn et al., and the benefit of ribociclib for the HER2-E subtype shown in the MONALEESA trials, suggests that there could be a role for CDK4/6 inhibitors in patients with ER+/HER2+ breast cancer, which is also consistent with preclinical data20. Here, CDK4 is linked to breast cancer.