In the setting of NSCLC, thymidylate synthase renders cancer cells resistant to the chemotherapeutic drug pemetrexed, while in patients with SCLC, it may, in part, be responsible for the lower efficacy of the drug combination pemetrexed and carboplatin in comparison with the chemotherapeutic regimen of etoposide plus carboplatin [36,37,38]. Here, TYMS is linked to small cell lung carcinoma.