Good Response to Pemetrexed after Treatment Failure with Another Thymidylate Synthase Inhibitor in Lung Adenocarcinoma: A Case Report

Pemetrexed is an antimetabolic agent and is well-known as a potent inhibitor of thymidylate synthase (TS). It also inhibits dihydrofolate reductase (DHFR) and glycinamide ribonucleotide formyl transferase (GARFT). We reported an intriguing case in which a non-small cell lung cancer patient who was refractory to pretreatment with S-1, a strong TS inhibitor, showed good response to pemetrexed treatment.