Radiotherapy Effect on Long-Term Net Survival Benefit for Early-Stage Diffuse Large B-Cell Lymphoma in the Rituximab Era

Abstract

It is controversial whether to add consolidative radiotherapy (RT) after chemoimmunotherapy in the first-line treatment for diffuse large B-cell lymphoma (DLBCL). This study aimed to investigate the long-term net survival benefit of RT for early-stage DLBCL in the rituximab era. The data of 10,841 adult patients with early-stage DLBCL from the Surveillance, Epidemiology, and End Results (SEER) database between 2002 and 2015 were extracted and analyzed. The patients had received combined modality treatment (CMT, chemotherapy plus RT) or chemotherapy alone. Linear regression analysis was performed for RT utilization by year of diagnosis. Competing risk analysis was used to evaluate the cumulative incidence of mortality according to the cause of death. Inverse probability of treatment weighting (IPTW) was used to balance the distribution of covariates between treatment arms. Relative survival (RS), standardized mortality ratio (SMR), and transformed Cox regression were performed to estimate the net survival benefit of RT by controlling for background mortality. Linear regression revealed that the slope of the best-fit line for RT utilization over time was negative between 2002 and 2015 (m = -0.006, P = 0.003). A total of 4,648 deaths were recorded among 10,841 patients; 55.6% were lymphoma-related death (LRD), and 44.4% were attributed to other causes. Patients initially treated with CMT had a lower cumulative incidence of LRD than chemotherapy alone (HR 0.63, 95% CI: 0.57-0.69; P < 0.001). The 10-year overall survival (OS) rate of 66.1%, RS rate of 85.0%, and SMR of 1.71 achieved with CMT were significantly better than chemotherapy alone (OS, 53.0%; RS, 69.8%; SMR, 2.62; P < 0.001). By IPTW and multivariable analysis, the addition of RT remained associated with better OS (HR 0.67, 95% CI: 0.62-0.71; P < 0.001) and RS (HR 0.69, 95% CI: 0.65-0.74; P < 0.001). RT was associated with better long-term net survival in patients with early-stage DLBCL in the rituximab era.