Among the four MCTs, MCT4 is mainly expressed in glycolytic tissues, such as muscles and tumour tissues [10–13], and overexpression of MCT4 is associated with poor prognosis in patients with a plethora of tumours [14–16], including non-small cell lung cancer (NSCLC), breast cancer, cervical cancer, colorectal cancer, oesophageal adenocarcinoma, hepatocellular carcinoma and melanoma [17]. This evidence concerns the gene SLC16A3 and breast cancer.