Decreased lymphoma-related deaths and improved long-term relative survival with radiotherapy for early-stage diffuse large B-cell lymphoma in the rituximab era.

Background: We aimed to investigate the incidence of lymphoma-related death (LRD) and the long-term net survival benefit of radiotherapy (RT) for early-stage diffuse large B-cell lymphoma (DLBCL) in the rituximab era.

Methods: 10,841 adults diagnosed with early-stage DLBCL between 2002-2015 were retrospectively analyzed using data from the Surveillance, Epidemiology, and End Results database. Primary therapy was categorized into combined-modality treatment (CMT, n = 3,631) and chemotherapy alone (n = 7,210). Competing risk analysis was used to evaluate the cumulative incidence of mortality. Inverse probability of treatment weighting (IPTW) was used to balance groups. The net survival benefit of RT was estimated through relative survival (RS), standardized mortality ratio (SMR), and transformed Cox regression, while controlling for background mortality.

Results: Patients initially treated with CMT had a lower cumulative incidence of LRD compared to those who received chemotherapy alone (HR 0.63, 95%CI: 0.57-0.69; P < 0.001). The 10-year overall survival (OS), RS, and SMR for CMT were 66.1%, 85.0%, and 1.71 respectively, which were significantly better than those for chemotherapy alone (53.0%; 69.8%; 2.62; all P < 0.001). IPTW and multivariable analysis revealed that the addition of RT led to 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). Moreover, compared with chemotherapy alone, the benefit of OS and RS for CMT increased over time within 10 years of diagnosis.

Conclusion: RT reduced LRD and improved the long-term net survival in early-stage DLBCL in the rituximab era. Further prospective studies are warranted to assess the specific patient population that would benefit the most from consolidative RT in early-stage DLBCL.