Extended Use of Rituximab in Older Adults with Non-Hodgkin Lymphoma
Authors: Matasar Matthew J. , Atoria Coral L. , Elkin Elena B. , Nabhan Chadi 
Published: October 2019

Abstract
Background: The introduction of rituximab has improved outcomes in B-cell non-Hodgkin lymphoma (BCL) across all histologies. Extended use of rituximab, or maintenance rituximab, improves progression-free survival in follicular lymphoma (FL) patients who achieve a response to induction rituximab with or without chemotherapy, but there is no evidence of an overall survival benefit. There is currently little evidence to support extended use of rituximab in other histologic subgroups, and older patients in particular may be at risk of adverse events. Our objective was to characterize patterns and predictors of extended rituximab therapy in a population-based cohort of older BCL patients in the United States.
Methods: In the Surveillance, Epidemiology and End Results (SEER)-Medicare dataset,we identified patients 66 years and older diagnosed with BCL in 2000-2010. Histology was classified as diffuse large B-cell lymphoma (DLBCL), Burkitt lymphoma (BL), FL, mantle cell lymphoma (MCL), other indolent BCL, and BCL not otherwise specified (NOS). We identified Medicare claims for rituximab starting at any point following diagnosis. Extended rituximab therapy was defined as a duration of greater than 7 months with no gap in rituximab claims greater than 6 months. Demographic and clinical characteristics associated with extended rituximab were evaluated in multivariable logistic regression.
Results: There were 24,232 BCL patients who received rituximab during the study period. The cohort was predominantly white (91%), half were men, 15% had a Charlson comorbidity score ≥2, and 12% were 85 years or older. DLBCL was the most common histology (44%), followed by FL (21%), other indolent BCL (17%), BCL-NOS (13%), MCL (6%), and BL (1%). Overall, most patients (85%) received rituximab for ≤7 months, but duration varied by histology (Table 1). More than a quarter of FL patients had extended therapy, including 7% who had rituximab for more than 24 months. Among patients with other histologies, receipt of extended therapy varied from 20% (other indolent BCL) to 8% (BL). Compared with FL patients and controlling for demographic and disease characteristics, patients with other histologies were less likely to receive extended rituximab therapy (p<0.0001). Adjusted odds ratios were 0.91 (95% CI 0.78-1.05) for MCL, 0.83 (0.75-0.91) for other indolent BCL, 0.67 (0.60-0.75) for BCL-NOS, 0.32 (0.29-0.36) for DLBCL, and 0.28 (0.15-0.53) for BL. However, 75% of patients who had extended rituximab, and 63% of those who had rituximab >24 months, were of non-FL histology. Controlling for histology and other characteristics, extended rituximab therapy was more likely among women (adjusted OR 1.09, 95% CI 1.01-1.18), and less likely among unmarried patients (0.92, 0.85-0.99) and those in rural areas (0.84, 0.75-0.94). There was significant regional variation (p<0.0001), with patients in the West (adjusted OR 0.86, 95% CI 0.79-0.95), and Midwest (0.75, 0.66-0.86) less likely to receive extended rituximab than those in the Northeast. There was no significant relationship between extended therapy and age, race, or comorbidity.
Conclusions: While FL patients were more likely than others to receive extended rituximab, the majority of patients receiving extended rituximab had other diagnoses across the entire spectrum of B-cell lymphoma, for which extended rituximab is neither indicated nor supported by guidelines or prospective data. After controlling for histology, several demographic characteristics significantly influenced the duration of therapy. Extended use of rituximab – particularly in patients for whom it is not clearly indicated – may have important implications for clinical outcomes, toxicity, and costs.
Table 1 Duration of rituximab use across B-cell lymphoma histologic subgroups Histology Duration of Rituximab N ≤7 mos >7-24 mos >24 mos DLBCL 10,567 91% 7% 2% FL 5,001 76% 17% 7% BL 127 92% 6% 2% MCL 1,339 79% 16% 5% Other indolent 4,095 80% 15% 5% BCL NOS 3,103 83% 13% 4% Total 24,232 80% 15% 5%

Disclosures
Matasar: Merck: Research Funding; GlaxoSmithKline: Research Funding; Genentech: Honoraria; Spectrum: Honoraria. Nabhan:Celgene: Honoraria, Research Funding.