CDK4 and breast cancer: Clinical data beyond ER-positive breast cancer are currently sparse: single-arm studies have been performed in a variety of cancer types with genomic alterations that are predicted to enhance sensitivity to CDK4/6 inhibition including human epidermal growth factor receptor 2 (HER2)-positive breast cancer, mantle cell lymphoma, liposarcoma, melanoma, non-small cell lung cancer, glioblastoma, neuroblastoma, and malignant rhabdoid tumors [37,38,39,40].