CDK4 and cancer: This hypothesis also provides a potential mechanism to explain how a cyclic amphiphilic peptide anticancer agent with a warhead homologous to the Pro‐Arg‐Gly‐Pro‐Arg‐Pro sequence in a non‐kinase (NK) region on an external loop in the C′‐terminus of Cdk4, selectively kills cancer cells but not normal cells by depriving them of energy, in contrast to the classical anticancer drug mechanism of attacking their replication.