External addition of 20 mM lactate reversed the phenotype toward chemoresistance [100], and was associated with an increased activity of genes coding for proteins whose oncogenic potential was shown in various cancer models (STAT3 and HIF-1α), the earlier mentioned LDHA, lactate receptor—HCAR1 (hydroxycarboxylic acid receptor 1/GPR81) and ABCB1 (ATP binding cassette subfamily B member 1; also known as MDR1 or P-glycoprotein). This evidence concerns the gene HCAR1 and cancer.