In preliminary laboratory science studies, the investigators show that proton pump inhibitors (PPIs) effectively inhibit human fatty acid synthase (FASN) and breast cancer cell survival. A preliminary retrospective study shows that PPI usage in breast cancer patients during chemotherapy significantly improved overall survival. The impact was most striking in patients with triple negative breast cancer (TNBC). Thus, PPIs may be repositioned as safe and effective breast cancer drugs to enhance the effect of chemotherapy.