Increased Serum Beta-2 Microglobulin during Induction Chemotherapy Associated with Poor Prognosis in Primary Central Nervous System Lymphoma

Introduction Primary central nervous system lymphoma (PCNSL) is a rare extra-nodal non-Hodgkin lymphoma that exclusively involves the brain, leptomeninges, eyes, or spinal cord. Due to the rare incidence of PCNSL, therapeutic decisions and predictions of outcomes rely on phase 2 clinical trials and retrospective studies. Indeed, it is important to continuously search potential prognostic factors. Serum beta-2 microglobulin (B2MG) is thought to be associated with prognosis in several lymphomas and multiple myeloma. Previous study in our center showed that increased serum B2MG of ≥ 1.8 μg/mL at diagnosis was associated with poor prognosis in PCNSL. In this study, we investigated association of serum B2MG level changes with survival outcomes in PCNSL patients during induction chemotherapy who had elevated serum B2MG level at diagnosis.

Methods We retrospectively reviewed prospectively collected PCNSL registry data for patients treated from March 1993 to May 2017 at Asan Medical Center in Seoul, Korea. Patients with serum B2MG of ≥ 1.8 μg/mL at diagnosis who had at least two or more measurement of serum B2MG including at diagnosis, 6 weeks, and 3 months from the initiation of induction chemotherapy were included in the analysis. Two weeks of window period was allowed for measured B2MG at 6 weeks and 3 months from the beginning of treatment. Overall survival (OS) was defined as the time from the initiation of induction treatment to death from any cause, and progression-free survival (PFS) was defined as the time from the initiation of induction treatment to disease progression or death. Univariate analyses were performed to compare survival outcomes using log-rank tests. Multivariate analyses were performed to identify independent prognostic factors for PFS and OS using a Cox proportional hazards model.

ResultsAmong 241 patients with diagnosis of PCNSL, 42 patients were included in the study. Median follow-up period was 4.0 years (range, 0.1-9.7). Median OS and PFS was 2.3 years (95% CI 1.9-2.6), and 1.2 years (95% CI 0.6-1.8), respectively. Median age was 67 years old (range, 28-85) and 26 patients (61.9%) were male. All patients received methotrexate-based combination chemotherapy as induction treatment and 31 patients (88.6%) showed complete response or partial response as best responses. Ten patients (23.8%) received consolidation treatment with high-dose chemotherapy followed-by autologous stem cell transplantation. Patients were classified into two groups according to serum B2MG level difference compared to B2MG level at diagnosis with the B2MG level at 6 weeks and 3 months from the initiation of induction treatment. Median B2MG at diagnosis, 6 weeks, and 3 months was 2.4 μg/mL (range, 1.9-11.7), 2.5 μg/mL (range, 1.3-8.7), and 2.6 μg/mL (range, 1.4-8.7), respectively. There was no statistically significant difference in terms of OS between patients with increased B2MG level at 6 weeks (16 patients) and patients with no increment (10 patients) with median OS of 1.4 years (95% CI 0.1-2.8) and 3.0 years (95% CI 1.1-4.9), respectively (P = 0.065). Patients with increased B2MG level at 3 months (23 patients) significantly poor prognosis in terms of OS compared to patients with same or decreased level (13 patients). Median OS was 1.4 years (95% 0.6-2.3) for the increased patients and not reached in patients with no increment (P < 0.001). Multivariate analysis with other factors showed significantly poor outcomes in patients with increased serum B2MG level at 3 months from the initiation of induction treatment in terms of OS with hazard ratio of 14.3 (95% CI 2.1-100.0, P = 0.007).

Conclusion Among PCNSL patients who had serum B2MG level of ≥ 1.8 μg/mL at diagnosis, which was associated with poor prognosis in our previous study, patients with no increment of serum B2MG level at 3 months from the initiation of induction chemotherapy was associated with better survival outcomes in terms of OS compared to those with increased level.