Survival outcomes of whole pelvic vs. bladder-only radiation in muscle-invasive bladder cancer: A nationwide large-scale study.

4600 Background: Muscle-invasive bladder cancer (MIBC) is an aggressive malignancy traditionally managed with definitive surgery combined with systemic therapy. However, bladder-preservation approaches, including concurrent chemoradiation, offer alternatives for patients unfit for surgery. Within bladder-preservation, the choice between whole pelvic radiation (WP-RT) and bladder-only radiation (BO-RT) remains debated. WP-RT may address microscopic lymphatic disease, while BO-RT minimizes radiation toxicity. This study aims to compare survival outcomes between WP-RT and BO-RT utilizing the National Cancer Database. Methods: This retrospective study included patients with MIBC (T1-4a, N0-2, M0) from 2004-2020. It focused on individuals who received radiation therapy and underwent the maximum feasible local resection without definitive surgery. Kaplan-Meier analysis and a multivariate Cox proportional hazards model were used to evaluate survival outcomes based on the radiation field in patients with MIBC. Results: This study analyzed 18,659 patients with MIBC, including 18,092 who received BO-RT and 567 who underwent WP-RT. Among these, 71.76% received systemic therapy. Notably, the use of systemic therapy was more common in the WP-RT group (89.24%) compared to the BO-RT group (71.21%). The median overall survival was 23.33 months for patients treated with BO-RT compared to 38.7 months (Log rank P<0.001) for those who underwent WP-RT. In our adjusted analysis, patients treated with WP-RT had a 35% lower risk of death (HR: 0.65, 95% CI: 0.55–0.76, P < 0.001) compared to those receiving BO-RT, irrespective of receiving systemic therapy. Additionally, the use of concurrent chemoradiation was associated with a 50% reduction in the risk of death (HR: 0.50, 95% CI: 0.48–0.51, P < 0.001). Conclusions: This study found that in patients with MIBC, WP-RT was independently associated with better overall survival compared to BO-RT. These findings highlight the survival benefits of targeting microscopic lymphatic disease with WP-RT, while weighing the risks of associated toxicity. Additionally, Concurrent systemic therapy significantly reduced the risk of death, emphasizing its vital role in improving survival outcomes. Cox proportional model in patients with muscle invasive bladder cancer. Variable HR (95% CI) P-value Charlson Score 0 >=1 1.24 (1.20–1.29) < 0.001 Radiation Field Bladder Only Pelvic + Bladder 0.65 (0.55–0.76) < 0.001 Histology Urothelial Non-Urothelial 1.23 (1.16–1.30) < 0.001 Concurrent Chemoradiation No Yes 0.50 (0.48–0.51) < 0.001