Background: BC2001 showed that adding chemotherapy (5FU+MMC) to radiotherapy significantly improved rates of muscle invasive bladder cancer (MIBC) locoregional control (LRC) [James 2012] but that reduced high dose volume RT rather than standard RT did not significantly reduce late side effects [Huddart 2013]. Here we present an update of the time to event outcomes after a median 10 years follow up. Methods: Under the 2x2 partial factorial design, 458 pts were randomised to RT (178) or cRT (182) (CT comparison) and/or to stRT (108) or RHDVRT (111) (RT comparison). Primary endpoint was LRC, secondary endpoints included overall survival (OS), bladder-cancer specific survival (BCSS), metastasis free survival (MFS) and salvage cystectomy rates. Results: Median follow up was 118 months (95%CI: 112-122). LRC and invasive LRC (ILRC) were improved with cRT (Table 1). Though no statistically significant differences between groups were found in OS, cRT exhibited a trend towards improvement in BCSS, significant when adjusted by known prognostic factors. Similar trend was found for MFS. Salvage cystectomy rate was lower for cRT (2-year rate, cRT:11% vs RT:17%, p=0.03). No differences between stRT and RHDVRT were found for any trial endpoint. Conclusions: With extended follow-up, an improvement in LRC and a reduced salvage cystectomy rate is confirmed with cRT. After adjustment for known prognostic factors this results in an improvement in BCSS. This updated data supports the use of cRT with 5FU/MMC and confirms this should be a standard of care for this patient population. Clinical trial information: ISRCTN68324339.

*Log rank test, stratified by RT treatment; ^**Adjusted Cox p-value.¹ Cox hazard ratio (HR) adjusted by RT group; ² HR adjusted by RT group and dose, neoadjuvant CT, age, stage, grade, multiple tumours and WHO status.