Overall, our results demonstrated that chronic hypoxia induced acidosis, one of the most obvious tumor microenvironments, which reduced the BMAL1 circadian clock gene via inhibition of transcriptional activity and decreased protein stability in breast cancer, and reduced BMAL1 promoted metastatic potency, which could be prevented by targeting tumor acidosis using melatonin via inhibition of LDH-A (Figure 6e). Here, BMAL1 is linked to breast cancer.