In further studies, Tseng et al. showed that Apigenin inhibited breast cancer cell (MDA-MB-231 line) proliferation-inducing G2/M cell cycle arrest through a double action: by suppressing the expression of cyclin A, cyclin B, and cyclin-dependent kinase-1 (CDK1), and upregulating p21, a known downstream effector of the p53 tumor suppressor protein [99]. This evidence concerns the gene CDK1 and breast cancer.