A phase II trial of risk enabled therapy after initiating neoadjuvant chemotherapy for bladder cancer (RETAIN BLADDER): Interim analysis

397 Background: Cisplatin-based neoadjuvant chemotherapy (NAC) followed by cystectomy (Cx) or chemoradiation (CRT) is the standard of care for urothelial carcinoma (UC) pts with muscle invasive bladder cancer (MIBC). Both Cx and CRT have potential short and long-term toxicity and QOL implications. Mutations in DNA damage repair/response genes are associated with pathologic downstaging after NAC. Methods: We conducted a phase II, multi-institutional clinical trial (NCT02710734) to evaluate a risk-adapted approach to treatment of MIBC. Pts with cT2-T3N0M0 UC of the bladder, ECOG PS 0-1 and CrCl≥50 mL/min, underwent NAC with accelerated methotrexate, vinblastine, doxorubicin, and cisplatin (AMVAC). Pre-NAC TURBT specimens were sequenced (Caris Life Sciences) for mutations (pathogenic or VUS) in ATM, ERCC2, FANCC or RB1. Pts with at least one mutation and no clinical evidence of disease by restaging TUR and imaging post-NAC began pre-defined active surveillance (AS). Remaining pts underwent bladder-directed therapy: intravesical therapy ( < cT2 post-NAC), CRT or Cx. The primary endpoint was metastasis-free survival (MFS) at 2 years which is not mature. We herein report key interim results of clinically-meaningful intermediate endpoints. Results: Seventy-one (ITT) pts were enrolled over 33 months at four academic centers. Median age was 70 years (47-83), 74% were male, 92% Caucasian, 81% ECOG PS 0 and 79% cT2. 90% completed 3 cycles of NAC and with 17% grade 3-4 TRAEs and one death during AMVAC. At the time of data cut-off (September 11, 2020), for the ITT pts, 32 pts have had a Cx, 5 underwent CRT and 7 underwent intravesical therapy, at some point during the trial. Thirty-three pts (46%) had a mutation of interest and 28 pts (39%) started AS (2 of the 28 pts on AS did not have a mutation but elected to start AS after achieving cT0 post AMVAC). 76% of those with a mutation were cT0 at post-NAC TURBT. With a median follow-up of 14.9 mo (range: 3.1-35.3 mo), 14 AS pts recurred (50%). Of the 14 recurrences, 2 recurred with locally advanced or metastatic disease and have died, 5 had MIBC with one eventual metastatic recurrence, and 7 had NMIBC. Six (14%) non-AS pts have died. Out of the 40 pts who did not go to upfront Cx [AS (N = 28), CRT (N = 5), intravesical tx (N = 7)], 3 (7.5%) (all in the AS group) went on to Cx later. The bladder preservation rate is 55% for ITT pts and 89% for the AS group. In the AS cohort, mutations were seen in RB1 (50%), ATM (42%), ERCC2 (31%), FANCC (4%) with lowest rate for recurrence in ERCC2 (25% recurrence) vs RB1 (62% recurrence). Conclusions: Interim results of a phase II trial of risk enabled therapy utilizing a selection of clinical and genomic factors in pts with cT2-T3 MIBC demonstrates a 50% rate of any UC recurrence and a 11% rate of locally advanced/metastatic disease in the AS group. 89% of AS pts have retained their bladder. Follow-up continues for the primary endpoint of 2-year MFS. Clinical trial information: NCT02710734.