Background: Transurethral resection of bladder tumor (TURBT) plus systemic therapy has been known for decades to achieve durable bladder-intact survival in a subset of patients with MIBC but efforts to advance this paradigm have been complicated by a lack of (a) prospective studies, (b) rigorous approaches to assess and define clinical complete response (cCR), and (c) integration of novel therapies. Methods: Eligible patients were cisplatin-eligible with cT2-T4aN0M0 urothelial bladder cancer. Patients received 4 cycles of gemcitabine, cisplatin, plus nivolumab followed by clinical restaging including urine cytology, MRI/CT of the bladder, cystoscopy and bladder biopsies. Patients achieving a cCR (normal cytology, imaging, and cT0/Ta) were eligible to proceed without cystectomy and receive nivolumab q2 weeks x 8 followed by surveillance. Patients not achieving cCR were recommended to undergo cystectomy. Coprimary endpoints included (1) cCR rate and (2) association between cCR and 2-year outcomes. The key secondary endpoint was the impact of pre-specified baseline genomic alterations on outcomes. Additional biomarkers to refine patient selection were also explored. Results: Between 8/2018-11/2020, 76 patients were enrolled at 7 sites (male 79%, median age 69; cT2 = 56%, cT3 = 32%, cT4 = 12%). Median follow-up is 27 months. 72/76 patients underwent clinical restaging and a cCR was achieved in 33/76 (43%; 95% CI: 32%, 55%). One cCR patient opted for immediate cystectomy (ypTaN0M0). Outcomes are summarized in the Table. Baseline ERCC2, ATM, FANCC, or RB1 alterations were not, but tumor mutational burden ≥ 10 mutations/mb was, significantly associated with the composite endpoint of ypT0 (immediate cystectomy) or 2-year bladder-intact metastasis-free survival (BIMFS). On landmark analysis, VI-RADS (Vesical Imaging–Reporting and Data System) score (3-5 versus 1-2) on restaging MRI (central blinded review) was associated with inferior BIMFS (HR 4.5; p = <0.01) and MFS (HR 19.3; p <0.01). Circulating tumor DNA data will be presented at the meeting. Conclusions: TURBT followed by gemcitabine, cisplatin, plus nivolumab achieves stringently defined cCR in a substantial subset of patients with MIBC. ≥2-year bladder-intact survival is achieved in the majority of patients with a cCR. Clinical trial information: NCT03558087.