CDK4 and breast carcinoma: According to the approval numbers obtained from the ClinicalTrials.gov database, in addition to the use of single agent CDK4/6 inhibitors in anti-cancer such as anti-HCC treatment (Identifier: NCT01356628; NCT03109886; NCT02524119), several clinical trials combining CDK4/6 inhibitors (Palbociclib, Ribociclib, or Abemaciclib) with immune-checkpoint inhibitors for breast cancer (Identifier: NCT03294694; NCT02791334; NCT02779751), ovarian cancer (Identifier: NCT03294694), and non-small cell lung cancer (Identifier: NCT02779751) are ongoing or active (28).