CDKN1B and breast cancer: P27KIP1 is also a CDK inhibitor protein known to function in regulating the G1-S transition, and P27KIP1 deficiency has been clinically associated with poor outcomes in breast cancer patients (Alkarain and Slingerland, 2004; Besson et al, 2008; Chu et al, 2008; Razavipour et al, 2020).