Safety evaluation of combined PD1+CTLA4 inhibition concurrently to chemoradiotherapy (CRT) in localized muscle invasive bladder carcinoma (MIBC)

Background: Neoadjuvant nivolumab (nivo) + ipilimumab (ipi) prior to radical cystectomy showed efficacy in localized MIBC. The safety of PD-1 and PDL-1+CTLA4 inhibition concurrent with CRT in localized MIBC has not been assessed. We present the first clinical trial data on concurrent 3 doses of q4w nivo 480mg (cohort1) and concurrent 4 doses of q3w nivo 3mg/kg + ipi 1kg/mg (nivo3+ipi1, cohort2) in combination with Mitomycin C/Capecitabin (MMC/Cape) CRT. Methods: We report the first 2 cohorts of a phase 1b, EC approved, study with nivo only or nivo3+ipi1 added to MMC/Cape CRT. CRT consists of MMC i.v. on day 1 with Cape 750mg/m2 on days of radiotherapy. Radiotherapy schedule comprises a 20x2Gy whole bladder irradiation with a simultaneous tumorboost of 20x0.75Gy. Patients with MIBC, T2-4N0-1, ECOG performance status <2 were included. A dose escalation scheme, with a staggered enrollment is used. The first 10 patients received nivo 480mg on week 1, 5, 9. Cohort2 of 10 patients received nivo3+ ipi1 at week 1, 4, 7 and 10. Relevant severe Adverse Events (AEs) were registered as Dose Limiting Toxicity (DLT) when they occurred within 6 weeks after start of treatment. Clinical efficacy is evaluated by cystoscopy and CT at week 12 and 24. Results: Both cohorts enrolled 10 patients. Median age was 68 [IQR 61-75] and 70 [IQR 66-75] years in cohort1 and 2, respectively. In cohort1 no patients experienced DLT. No dose reductions were applied. In cohort2, 2 patients experienced DLT, 1 trombocytopenia (grade 4) and 1 asystole (grade 5). 50% of patients did not receive all 4 q3w nivo3+ipi1 infusions, due to AEs. Table 1 reports an overview of AEs. In cohort2 6 SAE's occurred in 3 patients. Median follow up is 71 [IQR 59-86] and 30 weeks [IQR 12-45] in cohort1 and 2, respectively. 1year OS and DFS is 100% in cohort1. Conclusions: Concurrent 3 doses nivo 480mg q4w added to MMC/Cape based CRT is feasible with a favorable toxicity profile and shows promising efficacy in MIBC patients. An escalated regimen with 4 doses nivo 3mg/kg + ipi 1mg/kg q3w concurrent to CRT shows acceptable toxicity. Cohort3 with ipi 3mg/kg and nivo 1mg/kg is enrolling.