Impact of Folinic Acid Dosing on Efficacy and Toxicity of High-Dose Methotrexate in Central Nervous System Lymphoma
Authors: Haran Arnon , Gros Even-Zohar Noa , Lebel Eyal , Aumann Shlomzion , Shaulov Adir , Gatt Moshe E , Nachmias Boaz 
Published: December 2023

Treatment of primary central nervous system lymphoma (PCNSL) is centered around a backbone of high-dose methotrexate (HDMTX) with folinic acid (FA) rescue. Higher FA doses were associated with treatment failure in several retrospective studies in acute lymphatic leukemia (ALL), leading to the adoption of lower FA doses in ALL treatment protocols. In PCNSL, FA doses have varied widely, guidelines and consensus statements generally do not address FA dosing, and the effect of FA dosing on treatment outcomes has not been assessed. We retrospectively analyzed the medical records of patients treated at our institute for PCNSL between the years 2014 and 2022 to address this question.

Patient characteristics are listed in table 1. Complete dosing data was available for 36 patients. The median number of HDMTX doses administered was 6.5 (range, 2-9;), with an average dose of 3.9 g/m 2 (SD +/- 0.74; range, 2.7-5.0). Per the local protocol, IV FA rescue began 24 hours after each MTX infusion at a fixed dose of 50 mg four times daily and continued until MTX clearance. The average cumulative dose of FA administered per treatment was 322 mg/m 2 (SD +/- 141; range, 140-700). 33 patients (92%) achieved either a partial or complete response on MRI following induction treatment. Three (8%) had progressive disease. 26 patients (72%) proceeded with consolidation treatment. Of these, 16 (44%) underwent autologous hematopoietic stem cell transplant.

At a median follow up of 1.6 years (range, 0.3-8.1), 12 patients (33%) suffered progressive disease, disease relapse, or death. The 2-year PFS probability for the entire cohort was estimated at 64.5% (95% confidence interval [CI], 49.4-84.1%), and the 2-year OS as 70.7% (95% CI 56.0-89.2%). In univariate Cox regression analysis, average FA dose during MTX treatment was a significant predictor of both PFS and OS, with hazard ratios (HR) of 2.22 (95% CI 1.39-3.55; p &lt; 0.001) and 2.07 (95% CI 1.31-3.29; p = 0.002), respectively, for each 100 mg/m 2 increase. The FA dose during the first treatment cycle, before assessment of response, was also significantly associated with worse PFS (HR 1.56; 95% CI 1.24-1.96; p &lt; 0.001) and OS (HR 1.41; 95% CI 1.14-1.74; p = 0.001). A trend towards worse PFS and OS was seen with male gender, elevated serum LDH, and deep structure involvement.

A Cox multivariate regression analysis using the variables age, gender, serum LDH, deep structure involvement, and the average MTX and FA doses, identified FA dose as an independent prognostic factor for PFS, with an estimated hazard ratio (HR) of 2.23 for each 100 mg/m 2 increase (95% CI, 1.25-3.97; p = 0.006). A smaller effect was seen when the FA dose during only the first treatment cycle was examined (HR 1.55; 95% CI 1.16-2.08; p = 0.003). Involvement of deep structures was also significantly associated with worse PFS, with an estimated HR of 8.59 (95% CI, 1.28-57.5; p = 0.027), and there was a borderline significant trend for worse PFS with male gender and elevated LDH. None of the examined variables were identified as statistically significant predictors of OS in the multivariate analysis.

Logistic regression with 2-year PFS as the dependent variable was used to define a cutoff value of 350 mg/m 2 for FA dose. The group of patients who received FA doses above and below this threshold showed significantly different PFS curves (figure 1). The 2-year PFS probability was estimated at 56.6% (95% CI, 35.4-90.5%) for patients who received doses of FA above this threshold, and 70.5% (95% CI, 51.7%-96.2%) for patients who received doses below it.

We identified no effect of FA dosing on hematologic, renal, hepatic, or gastrointestinal toxicity at the dose ranges examined.

In summary, we found that high FA doses were associated with inferior PFS in PCNSL. Such high doses may be avoided through use of lower individual doses of FA, such as 15 mg/m 2 or 25 mg fixed doses as have been used in some protocols, rather than the 50 mg or higher doses used in our and other's practice. Our conclusions are moderated by the study's limitations, which include a small sample size limited to a single center and a retrospective design. However, they suggest that optimizing FA dosing in treatment of PCNSL might improve treatment efficacy without excess toxicity. Future larger and prospective studies will be required to better define the range of MTX and FA doses at which the balance between prevention of treatment toxicity and preservation of treatment efficacy is preserved.