A recent study presented at the 2024 International Bladder Cancer Network (IBCN) Annual Meeting suggests that whole-pelvis radiation therapy may offer a survival benefit for patients with muscle-invasive bladder cancer. The research, led by Dr. Gautier Marcq, explored the impact of radiation field size on oncological outcomes in this patient population.
The study utilized a large Canadian multicenter collaborative database, analyzing data from 809 patients with muscle-invasive bladder cancer (cT2-4aN0-2M0) who underwent curative radiation therapy. Patients were categorized into two groups based on the radiation therapy volume: whole-pelvis radiation therapy versus bladder-only radiation therapy. The median follow-up was 54 months (95% CI 46-60).
Study Design and Patient Characteristics
After applying exclusion criteria, the final cohort included 599 patients, with 369 (61.6%) receiving whole-pelvis radiation therapy. Notably, patients undergoing whole-pelvis radiation therapy were younger and more likely to present with node-positive disease and lymphovascular invasion. They also more frequently received neoadjuvant and concurrent chemotherapy. To account for these differences, the researchers employed inverse probability of treatment weighting (IPTW) to balance covariates between the two treatment groups.
Key Findings: Survival Benefit with Whole-Pelvis Radiation
Approximately three months post-radiotherapy, 76% of patients achieved a complete response. Multivariable analysis revealed that hydronephrosis (OR 0.45, 95% CI 0.28-0.71) was the only predictor of lower odds of complete response. While whole-pelvis radiation therapy did not significantly impact complete response rates (OR 1.14, 95% CI 0.76-1.72; p = 0.526), it was significantly associated with improved cancer-specific survival (HR 0.66, 95% CI 0.47-0.93; p = 0.016) and overall survival (HR 0.68, 95% CI 0.54-0.87; p = 0.002), independent of other prognostic factors.
Sensitivity Analyses and Limitations
Dr. Marcq and his team conducted several sensitivity analyses (T2-T3 cN0 cM0, TMT, hypofractionated regimen), which consistently demonstrated improved survival with whole-pelvis radiation therapy. However, the authors acknowledged the study's limitations, including its retrospective design and the heterogeneity of radiotherapy regimens used. They also emphasized the need for prospective validation to confirm these findings.
Clinical Implications
The study suggests that pelvic lymph node irradiation may improve survival outcomes in patients with muscle-invasive bladder cancer undergoing curative-intent radiation therapy. While prospective validation is ideal, the practical challenges of conducting such a trial may limit its feasibility. These findings contribute valuable insights to the ongoing debate regarding the optimal radiation field size in the treatment of muscle-invasive bladder cancer.
