CDKN1A and breast cancer: We noticed a time-dependent increase of P21 expression in tested breast cancer cells and increased P-P53 expression in ZR-75-1 cells treated with 100 μg/mL of rGO in comparison to untreated control cells after 24 and 48 h of incubation The Cdk inhibitor P21 may be induced by both P53-dependent and P53-independent mechanisms, and the induction of P21 is attributable to cell cycle arrest [48].