Introduction: Radiotherapy is an accepted treatment approach for well-selected patients with bladder cancer. Randomized control trials have shown superior outcomes to patients who receive concurrent chemotherapy compared to radiation monotherapy. However, there are limited data to guide selection of the optimal radio-sensitizing regimen. Methods: Canadian academic centres contributed to a retrospective cohort of muscle invasive (cT2-4N0-2) bladder cancer patients treated with curative-intent radiotherapy, with or without concurrent chemotherapy. Patients were stratified and analyzed by radio-sensitizing chemotherapy regimen. Outcomes were metastasis-free, cancer-specific, and overall survival (MFS, CSS, and OS). Results: Of 656 patients, 268 (41%) were treated with radiation monotherapy, 174 (27%) with cisplatin, 108 (16%) with gemcitabine, 74 (11%) with 5FU-MMC, and 32 (5%) with carboplatin. The median follow-up was 24 months (95% CI: 21 – 27). In the entire cohort, the median MFS was 35 months (95% CI: 29 – 44), median CSS not reached (95% CI: 94– not reached) and median OS 52 months (95% CI 42 – 60). Disease characteristics were similar between groups, but patients who received radio-sensitizing chemotherapy were younger and had fewer comorbidities. Compared to no chemotherapy, concurrent cisplatin was associated with improved MFS (HR 0.46; 95% CI: 0.35-0.60), CSS (HR 0.44; 95% CI: 0.31-0.64) and OS (HR 0.33; 95% CI: 0.24-0.43). Concurrent 5FU-MMC was also associated with improved MFS (HR 0.60; 95% CI: 0.40-0.88), CSS (HR 0.32; 95% CI: 0.16-0.66), and OS (HR 0.45; 95% CI: 0.28-0.71). Concurrent gemcitabine was associated with improved MFS (HR 0.77; 95%CI 0.58-1.02), CCS (0.76; 95%CI 0.49-1.27), and OS (HR 0.76; 95%CI 0.57-1.02). Concurrent carboplatin was associated with improved MFS (HR 0.55; 95% CI: 0.33-0.92), CSS (HR 0.64; 0.43-1.27), and OS (HR 0.52; 95% CI: 0.30-0.89). Conclusions: Patients with MIBC treated with RT have better oncologic outcomes with all forms of radio-sensitizing chemotherapy. While the best outcomes are associated with cisplatin, other radiosensitizers seem to be effective for platinum-ineligible patients. SOURCE OF Funding: None
