To investigate whether the level of TS expression affects the sensitivity of NSCLC cells to pemetrexed, we first established A549 (A549/TS1 and A549/TS2), H1299 (H1299/TS1 and H1299/TS2), and PC9 (PC9/TS1 and PC9/TS2) cells that stably overexpress TS. Here, TYMS is linked to non-small cell lung carcinoma.