CDK4 and neoplasm: Endocrine therapy such as aromatase inhibitors, fulvestrant or tamoxifen are used in patients with an HR+ tumor phenotype either alone [50], or more commonly in combination with any of the following kinase inhibitors, such as the CDK4/6 inhibitors (e.g., palbociclib, ribociclib, or abemaciclib), the mTOR inhibitor (e.g., everolimus), or the PI3K/AKT inhibitors (e.g., alpelisib, capivasertib) [51–54].