OBJECTIVE: The present study aims to investigate the correlation of 
polymorphisms of SLCO1B1 gene with the toxicity during therapy with the 
high-dose methotrexate (MTX) chemotherapy in childhood acute lymphoblastic 
leukemia.
METHODS: We analyzed 2 polymorphisms (rs4149081 and rs11045897) in SLCO1B1 gene 
in 280 Chinese pediatric B-ALL patients, using MTX plasma concentration as an 
objective and quantifiable marker of toxicity. We utilized Enzyme-multiplied 
immunoassay technique (EMIT) to measure the plasma concentration of MTX. The 
polymerase chain reaction-allele specific (PCR-AS) method was utilized to 
perform the genotyping.
RESULTS: We found there was a statistically significant association between MTX 
plasma concentration and the SLCO1B1 rs11045879 CC genotype (P<0.05). We also 
found the rs4149081 AA genotype was associated with high-MTX plasma 
concentrations. A-C haplotype carriers have a higher risk for MTX delayed 
clearance but G-T haplotype was associated with a lower risk for MTX delayed 
clearance.
CONCLUSIONS: The rs4149081 AA genotype and the rs11045897 CC genotype could be 
indicators for high-MTX plasma concentrations in children with ALL.