# Interactive Effect of Age on Overall and Relative Survival Benefits of Radiotherapy for Early-Stage Diffuse Large B-Cell Lymphoma in the Rituximab Era

## TL;DR

This study shows that radiotherapy benefits early-stage lymphoma patients more when given to younger individuals, especially in terms of overall and relative survival.

## Contribution

The study identifies a significant interaction between age and radiotherapy benefits in DLBCL, particularly highlighting greater benefits for younger patients.

## Key findings

- Radiotherapy improved survival across all age groups, with the greatest benefit observed in younger patients.
- Age significantly interacted with radiotherapy for both overall and relative survival outcomes.
- Relative survival was a valid alternative to overall survival for evaluating treatment benefits.

## Abstract

The aim of the study was to determine the interactive effect of age on overall survival (OS) and relative survival (RS) benefits of radiotherapy (RT) in early-stage diffuse large B-cell lymphoma (DLBCL).

Data for 10,841 adults with early-stage DLBCL from the Surveillance, Epidemiology, and End Results database between 2002 and 2015 were retrospectively analyzed. Primary therapy was classified as combined-modality treatment (CMT; n = 3,631) and chemotherapy alone (n = 7,210). Inverse probability of treatment weighting was used to balance covariate distribution between the treatment groups. Survival was estimated and compared using the Kaplan-Meier method and log-rank test, respectively. Age-RT interactive effect on survival was examined through Cox regression multiplicative interaction analysis.

Using age of 60 years as the reference, older age was an independent predictor of shorter OS in the multivariable Cox model (hazard ratio (HR), 1.07; 95% confidence interval (CI), 1.06–1.07; P < 0.001). After controlling for background mortality, older age was not an independent predictor of RS (HR, 1.00; 95% CI, 0.99–1.00; P = 0.842). Across all age groups, patients treated with CMT had better OS and RS than those who received chemotherapy alone. A significant interaction between age and RT was identified for both OS (Pinteraction = 0.020) and RS (Pinteraction = 0.038), indicating greater RT benefit in young patients. A linear correlation existed between RS and OS at the treatment arm level.

RT was associated with improved net survival across all ages, particularly for young adults. RS was a valid alternative endpoint for prognostication and benefit evaluation.