Phase II trial of atezolizumab in BCG-unresponsive non-muscle invasive bladder cancer: SWOG S1605 (NCT #02844816).

Abstract

5022 Background: Radical cystectomy (RC) is the standard of care for patients with BCG-unresponsive high risk non-muscle invasive bladder cancer (NMIBC), but many patients are unfit for surgery or elect bladder preservation. Based on the reported efficacy of atezolizumab in metastatic urothelial carcinoma and the known expression of PD-L1 in NMIBC after BCG therapy, this trial was designed to evaluate the activity of atezolizumab in BCG-unresponsive high risk NMIBC. Methods: This single arm phase II registration trial testing systemic atezolizumab (1200 mg IV) every 3 weeks for one year aimed to enroll 135 (70 CIS and 65 non-CIS) eligible patients with histologically proven BCG-unresponsive high risk NMIBC who were unfit for or declined RC. Here we report on the subset with CIS (with or without concomitant Ta/T1) among patients who received at least one protocol treatment. The primary endpoint was pathological complete response (CR) rate at 6 months as defined by mandatory biopsy with a null hypothesis of 30% and alternative of 50% with a 1-sided alpha = 0.05 and 96% power. The 3 month CR rate, defined by cytology, cystoscopy and for-cause biopsy, is reported here as a secondary endpoint, in addition to safety. Results: Seventy-five eligible CIS patients were enrolled. Two received no treatment and are not evaluable. Of 73, median patient age was 73.4 years and median number of prior BCG doses was 12. Concomitant Ta/T1 tumor was found in 30 (41.1%) patients, including T1 disease in 16 (21.9%). A CR was observed in 30 (41.1%; 95% CI 29.7%, 53.2%) patients at 3 months and 19 (26.0%; 95% CI 16.5%, 37.6%) at 6 months. Any possibly or probably treatment-related adverse event (AE) was observed in 61 (83.6%) patients. The most frequent AEs were fatigue 36 (49.3%), pruritis 8 (11.0%), hypothyroidism 8 (11.0%), and nausea 8 (11.0%). Grade 3-5 AEs occurred in 9 (12.3%) patients and there was one treatment-related death (myasthenia gravis with respiratory failure and sepsis). Conclusion: The observed response to atezolizumab at 3 and 6 months in patients with BCG-unresponsive CIS was similar to that reported in recent similar trials and meets the benchmark for initial CR defined by the FDA guidance. This trial provided no new safety concerns. The duration of response will determine if this is a suitable treatment option for patients with BCG-unresponsive high risk CIS. Clinical trial information: 02844816 .