MTHFR C677T genetic polymorphisms are not a decisive factor in delayed methotrexate excretion in central nervous...

High-dose methotrexate (HD-MTX) serves as a cornerstone treatment for central nervous system lymphoma. However, its clinical utility is limited by delayed drug excretion and associated adverse events. The methylenetetrahydrofolate reductase (MTHFR) C677T polymorphism, a critical genetic variant influencing MTX metabolism, has been proposed by some experts as an indicator for HD-MTX dose reduction due to its potential association with delayed excretion.

This study aimed to identify clinical risk factors for delayed MTX excretion and evaluate the predictive value of MTHFR C677T polymorphism in HD-MTX treatment cycles for CNS lymphoma patients.

We conducted a retrospective analysis of 213 HD-MTX treatment cycles in CNS lymphoma patients (derived from 98 patients) treated at our institution between May 2015 and December 2023. Each patient received a median of 3 HD-MTX cycles (range 1-9 cycles). Treatment cycles were stratified into delayed excretion (n = 66) and normal excretion (n = 147) groups based on international consensus guidelines for pharmacokinetic monitoring of serum MTX concentrations. MTHFR C677T genotypes were analyzed using PCR-RFLP with Sanger sequencing validation (10% random sample). Clinical parameters were compared between groups; univariate logistic regression (retention threshold: P < 0.10) was used for initial risk factor screening, and a mixed-effects logistic regression model with a random intercept for individual patients (retention: P < 0.05) was applied for identifying independent risk factors to correct for non-independence of repeated measures.

Univariate analysis revealed four potential risk factors (P < 0.1): advanced age (OR = 1.03), MTHFR C677T CT/TT (OR = 1.73), hypoalbuminemia (< 35 g/L) (OR = 3.42), and acidic urine pH (< 7.0) (OR = 4.15). Mixed-effects multivariate analysis identified hypoalbuminemia (adjusted OR = 3.02, 95%CI 1.56-5.85) and acidic urine pH (adjusted OR = 4.15, 95%CI 2.17-7.94) as independent predictors of delayed excretion (P < 0.05), with a random effect variance of σ²=0.21 indicating mild individual intervariability. The MTHFR C677T CT/TT genotype showed no statistically significant association in the adjusted model (P = 0.095). A total of 35.1% (13/37) of patients with CT/TT genotype exhibited delayed clearance in initial cycles (1-2) but normalized excretion in subsequent administrations (cycles 3-6, involving 42 treatment cycles). The median number of HD-MTX cycles administered was 4 (range 1-8) in patients with at least one delayed excretion cycle and 5 (range 1-9) in patients with all normal excretion cycles.

Our findings demonstrate that urine acidification and hypoalbuminemia, rather than MTHFR C677T polymorphism, constitute primary risk factors for HD-MTX excretion delay in treatment cycles. These results suggest that optimal management should prioritize urinary alkalinization (pH ≥ 7.0) and albumin level maintenance over genotype-guided dose reduction. These modifiable factors present actionable targets for improving HD-MTX safety profiles in CNS lymphoma treatment.