MTHFD1 and cancer: Since MTHFD2 does not perform an exclusive enzymatic reaction within the one-carbon pathway, and its dehydrogenase and cyclohydrolase catalytic activities are shared with other members of the MTHFD family, the mitochondrial MTHFD2L and the cytosolic MTHFD1, it is intriguing why the cancer cell particularly increases the expression of MTHFD2.