Aspirin and metformin exhibit antitumor activity in murine breast cancer.

Studies have shown that aspirin and metformin play important roles in chemoprevention and repression of breast cancers, even though the exact mechanism remains unclear. Aspirin is capable of stimulating apoptosis through prostaglandin-dependent or prostaglandin-independent pathways. Metformin inhibits cell growth by enhancing the tumor suppressive function of transforming growth factor (TGF-β). In the present study, we report a new link between aspirin, metformin, TGF-β1 and murine breast cancer inhibition. Specifically, we showed that aspirin and metformin enhanced 4T1 cell apoptosis by inducing secretion of TGF-β1, whereas estradiol weakened the effect.