An old but effective drug against diabetes can also help in the fight against breast cancer. Probably, if administered to healthy women it can prevent its insurgence. These are the important results of a study on metformin just published on Nature Communication, and conducted by the team of Giovanni Blandino of the National Cancer Institute Regina Elena (IRCCS). In this work metformin exerts some of its antitumor activities by reprogramming the metabolism of a tumor cell.