Moreover, MTHFD1 possesses additional enzymaticactivity as a 10-formyl tetrahydrofolate synthetase, converting 10-CHO-THFto formate.1,20 The key distinction between thesetwo proteins lie in their expression profiles: MTHFD1 is typicallyexpressed in normal cells while MTHFD2 is abundantly expressed inimmortal,21 embryonic,22 and cancer cells,4 but absentin adult normal cells.4 Therefore, designinginhibitors specifically against MTHFD2 holds promise for achievinga broader therapeutic window with minimized toxicity and fewer sideeffects. Here, MTHFD1 is linked to cancer.