SLC16A3 and neoplasm: Monocarboxylic acid transporter 4 (SLC16A3/MCT4) is one of the membrane protein stubs in cells that is structurally able to output lactic and pyruvic acids and affect the acidity of the tumor microenvironments.15, 16, 17 High expression of MCT4 has been reported to be a biomarker in various types of tumors,18, 19, 20, 21, 22, 23, 24 which makes it an appealing therapeutic target in cancers.