It has been shown that the block of cell proliferation and apoptosis induced by SHMT2 downregulation can be at least partially reverted by supplementing the growth medium with glycine demonstrating that the major role of this protein is in the serine/glycine conversion.12 Our experiments show that supplementation with serine or glycine fails to block the SHMT1-dependent induction of apoptosis, further supporting the idea that SHMT1 has a different and more important role in lung cancer cells other than the production of amino acids. Here, SHMT2 is linked to lung cancer.