Background: Chemoradiotherapy (cRT) with 5FU and Mitomycin C (5FU/MMC) is an accepted standard of care for muscle invasive bladder cancer. Cetuximab is an approved radio-sensitiser in head and neck cancer and EGFR is over-expressed in bladder cancer. We report a phase 1/2 trial of the addition of cetuximab to standard cRT. Methods: Phase 1/2 single-arm, multicentre, open-label study conducted in 5 UK centres. Treatment: RT: 64 Gy/32 fractions, 5FU 2.5g/m2 over days 1-5 & 22-26, MMC 12g/m2 day 1, cetuximab 400mg/m2 day -8, 200mg/m2 day 1 and weekly x7. Main inclusion criteria: T2-4aN0M0 urothelial cancer, PS 0-1; prior neoadjuvant therapy permitted. Endpoints: Phase 1; feasibility and safety of cRT with cetuximab + 5FU/MMC in combination. Phase 2; local control (LC) at 3 months. Secondary outcomes: invasive loco-regional progression free survival (LPFS), noninvasive LPFS, metastasis free survival (MFS), overall survival (OS) & patient reported outcomes (PROMs). Sample size; phase 1 between 6 and 18, phase 2 up to 45 including those recruited in phase 1. Results: Between Sept 2012 and Oct 2016, 33 patients were recruited; 7 in phase 1 26 in phase 2. Median age 70.1 (IQR 65.4-80.2) yrs, 60.6% WHO Performance Status 0; 81.8% male, 26/33 neoAd chemotherapy. 3 patients ineligible post registration. 30 evaluable pts started RT, 1 patient didn’t complete RT due to serious adverse event (interstitial pneumonitis), 3 with delays. Phase 1, 6/7 pts completed Cetux therapy, 1 omitted 1 dose for grade 3 rash. LC was 77% (95% CI 58, 90). Overall median dose intensities Cetux 100%, MMC 99% 5FU 99.8%. 8 pts developed recurrence; 2 MIBC. The 6 & 12 month muscle-invasive LPFS was 93 &; non-invasive LPFS 97% & 85%, MFS 90% & 90%, OS 97% & 87%. PROMs showed a transient dip at 1 mo, back to baseline at 3 mo. Conclusions: Phase 1 data demonstrate it’s feasible and safe to add cetuximab to cRT with 5FU/MMC with high delivered dose intensities. Although recruitment failed to reach the pre-specified target for phase 2 exploratory analysis indicate the 3 month bladder control rates and recurrence rates are above those reported in BC2001 with good PROMs provides evidence to consider further evaluation of cetuximab. Clinical trial information: 80733590.