AZD8421 is a potent and highly selective inhibitor of Cyclin-dependent Kinase 2 (CDK2), with an IC50 against CDK2 of 9nM with selectivity over CDK1, CDK4 and CDK6. It also exhibits an anti-proliferative effect, effectively inhibits Rb phosphorylation, and shows strong activity both as a monotherapy and in combination with CDK4/6 inhibitors in breast and ovarian cancer models.