Recently Lopez-Lopez et al. [180] analyzed 10 polymorphisms in seven genes [MTHFR, TS, SHMT1, RFC1, ABCB1, ABCG2, and SLCO1B1 (OATB1B1 gene)] from the MTX metabolism in Spanish pediatric B-ALL patients, and found a statistically significant association between MTX plasma concentration and the SLCo1B1 rs11045879 CC genotype or rs4149081 AA genotype. The gene discussed is SLCO1B1; the disease is precursor B-cell acute lymphoblastic leukemia.