This finding is consistent with a previous study, which indicated that intraperitoneal injection of L‐lactate and 3‐hydroxy‐butyrate (a ketone body) increased tumor growth by 2.5‐fold and stimulated the formation of lung metastases by 10‐fold in MDA‐MB‐231 breast cancer in a mouse model.33 What we knew about MCT4 was largely based upon experimental studies that investigated how MCT4 impacted the metabolism of a tumor. This evidence concerns the gene SLC16A3 and breast cancer.