Pemetrexed, a multitarget antifolate, is effective in non-squamous NSCLC and malignant pleural mesothelioma, with the main focus on inhibition of enzymes involved in pyrimidine and purine synthesis such as thymidylate synthase (TS), dihydrofolate reductase (DHFR) and glycinamide ribonucleotide formyltransferase (GARFT). The gene discussed is DHFR; the disease is non-small cell lung carcinoma.