CDK9 and neoplasm: As a vital direction for novel drug discovery, the therapeutic strategies of PROTAC have been successfully applied to conditionally degrade plenty of POIs in vitro and in vivo, such as estrogen receptor (ER) 7, androgen receptor (AR) 8, bromodomain-containing protein 4 (BRD4) 9-11, anaplastic lymphoma kinase (ALK) 12, 13, Focal adhesion kinase (FAK) 14, cyclin dependent kinase 9 (CDK9) 15, BCR-ABL1 16, 17, and cycle-related and expression-elevated protein in tumor (CREPT) 18.