Phase II/III clinical results of IL-15RαFc superagonist N-803 with BCG in BCG-unresponsive non-muscle invasive bladder cancer (NMIBC) carcinoma in situ (CIS) patients.

Abstract

510 Background: Patients with NMIBC CIS unresponsive to BCG have limited treatment options. N-803 (Anktiva) is a mutant IL-15-based immunostimulatory fusion protein complex (IL-15RαFc) that promotes proliferation and activation of natural killer (NK) cells and CD8+ T cells, but not regulatory T cells. Phase Ib data in BCG-naive patients with NMIBC demonstrate that intravesical administration of N-803 with BCG induced complete response in all patients, without recurrences for the study duration of 24 months. An open-label, 3 cohort multicenter phase II/III study (QUILT 3.032) of intravesical BCG plus N-803 in patients with BCG-unresponsive high-grade NMIBC (NCT03022825) was opened. We report here the interim analysis of Cohort A, BCG-unresponsive (CIS) [with or without Ta or T1 disease], as of December 2020 data cutoff. Methods: All treated patients received intravesical N-803 plus BCG, consistent with the standard induction/maintenance treatment schedule. The primary endpoint for Cohort A of this phase II/III study is incidence of complete response (CR) of CIS at any time. Results: To date, 80 patients have enrolled in cohort A of this phase II/III trial. Evaluable analysis at this time shows CR rate at any time of 72% (N=51/71); for patients achieving CR, the probability of maintaining a CR for 12 months is 59%, with a median duration of complete response of 19.2 (7.6, 26.4) months. Low-grade treatment related AEs include dysuria, hematuria, and pollakiurua (all 16%), urgency (14%), and bladder spasm (8%), all other AEs were seen at 6% or less. A total of 9 subjects experienced at least 1 treatment emergent SAE (Severe Adverse event), the SAE rate is 1% for any given AE. No treatment emergent SAE’s were considered treatment related. No immune related SAE’s have been seen. To date, 10/80 (12.5%) patients proceeded to cystectomy in this BCG unresponsive population. Conclusions:With a CR rate of 72%, N-803 has met its primary endpoint with 59% probability of CR patients maintaining CR for at least 12 months. With the observed strong efficacy and an SAE rate of 1%, N-803 represents a novel treatment option for BCG unresponsive CIS with a favorable benefit:risk ratio, in a therapeutically challenging disease. Clinical trial information: NCT03022825.