The multivariate analysis, adjusted for MTX administration route, showed that the ABCC1 rs2238476-AG genotype (AG vs. GG: OR = 8.10, 95% CI = 1.69–46.63, p = 0.011) and the FOXP3 rs3761548-GT genotype (OR = 4.11, 95% CI = 1.22–15.30, p = 0.027) were associated with a higher risk of having asthenia during MTX therapy (these values are shown in Table 6). This evidence concerns the gene ABCC1 and asthenia.