The 3 FDA-approved CDK4, 6 inhibitors, palbociclib, ribociclib, and abemciclib, all provided progression-free survival benefits when combined with endocrine therapy in advanced ER+/HER2- breast cancer. But, not all of them provided overall survival benefit in the same setting. One of the proposed mechanisms that influence the overall survival difference is from the different influence of the 3 CDK4, 6 inhibitors on tumor microenvironment and/ or immune system. However, there was no head-to-head comparison of the 3 CDK4, 6 inhibitors in the same study. Neoadjuvant therapy provides a window to obtain tissue samples before treatment, during treatment, and after treatment. We aim to compare the immune modulation effects of palbociclib, ribociclib, and abemaciclib with letrozole in neoadjuvant treatment for ER+/HER2- early breast cancer. We will collect tumor tissue, blood, and stool samples prospectively before treatment, at 2 weeks after treatment, and after 12 weeks of treatment at the time of surgery. Immune modulation effects will be compared between 3 treatment groups from breast tumor RNAseq analysis.
