Remarkably, ZMYND8 is found to regulate glycolysis in hypoxic breast cancer cells as well as in 4T1-induced breast tumors in mice, elevating the expression of hexokinase II (HKII) and lactate dehydrogenase A. Notably, ZMYND8 directly regulates the transcription of lactate dehydrogenase A by promoting the recruitment of S5-phosphorylated RNA polymerase II to its promoter region. This evidence concerns the gene ZMYND8 and breast cancer.