Further, elevated TS coupled with downregulation of FOLR1 (encoding FRα) and marginally upregulated expression of SLC19A1 and SLC46A1 (encoding reduced folate carriers) likely contributes to a relative lack of efficacy for anti-folate TS inhibitors in SCLC, including pemetrexed and raltitrexed. This evidence concerns the gene FOLR1 and small cell lung carcinoma.