AZD8421 is a selective CDK2 inhibitor (IC 50 : 9 nM) with selectivity for CDK1 , CDK4 and CDK6 . AZD8421 inhibits cancer cell proliferation by inhibiting pRB phosphorylation, inducing cell cycle arrest and senescence. AZD8421 demonstrated promising single efficacy and synergy with CDK4/6 inhibitors such as Palbociclib in in vivo breast and ovarian models. AZD8421 also has potent single-agent inhibitory activity against drug-resistant breast cancer cells.