Additional pre-clinical studies also demonstrate potential immuno-modulation by CDK4/6 inhibitors (CDK4/6i) in breast cancer and melanoma with upregulation of MHC Class I expression, T regulatory cell reduction, increased IFN-γ release in the tumor microenvironment and enhanced long-term anti-tumor immunity [17,18,19,20,21]. Here, CDK4 is linked to breast cancer.