Successful Use of High Dose Methotrexate in Treatment of Primary CNS Lymphoma Patients Without Access to Serum Methotrexate Levels Monitoring: Challenges and Outcome

High dose methotrexate (HDMTx) based chemotherapy forms the backbone of therapy for patients with Primary Central Nervous system Lymphoma (PCNSL). However, delivering HDMTx in resource constrained settings, especially without therapeutic drug monitoring, is difficult. We share our experience of treatment of patients with PCNSL at our center over a 10-year period with local adaptations made to deliver HDMTx. We retrospectively analysed the case records of patients diagnosed with a PCNSL over the course of 10 years from 2010 to 2020. Fifty-five patients received therapy for newly diagnosed PCNSL. Thirty-six patients received Modified De-Angelis protocol ± Rituximab with curative intent. Fourteen of these patients were unable to complete the protocol with the most common cause being development of methotrexate toxicity. Patients unable to complete the designated 5 cycles of HDMTx had a poorer PS and higher probability of having a high IELSG score at baseline. Nineteen patients were given non HDMTx based therapy either due to advanced age or poor performance status. Twenty-nine patients (52.7%) were able to achieve a complete response. The most common cause of mortality was relapse/progressive disease. The Median EFS and OS of the cohort was 29 months and 40 months respectively. All attempts should be made to have therapeutic drug level monitoring for administration of HDMTX based therapy for the patients with PCNSL, more so in patients who have poor performance status and a high IELSG score. If it is imperative to give HDMTx without access to TDM facility then a possible risk of higher toxicity should be explained to all patients, beforehand