ALDH18A1 and melanoma: ALDH18A1 not only regulates proline metabolism in cancer cells such as melanoma, NB and hepatocellular carcinoma cells but also controls the pentose phosphate pathway by altering the NADP+/NADPH ratio, which in turn regulates cell proliferation through nucleotide metabolism in cancer cells such as lymphoma, NSCLC and hepatocellular carcinoma cells57,.103