Keynote 57: A Phase II Clinical Trial to Study the Efficacy and Safety of Pembrolizumab (MK-3475) in Subjects With High Risk Non-muscle Invasive Bladder Cancer (NMIBC) Unresponsive to Bacillus Calmette-Guerin (BCG) Therapy

Merck Sharp & Dohme Corp
Study Design: 
Eligible patients had high-risk NMIBC unresponsive to BCG who refuse or are ineligible for cystectomy. Patients with papillary disease were fully resected prior to therapy. There were two cohorts: A) carcinoma in situ (CIS) with or without high grade papillary disease and B) high grade papillary disease without CIS. Subjects received pembrolizumab every 3 weeks and had standard cystoscopy, cytology, and if indicated, biopsy every 12 weeks for 2 years followed by every 24 weeks for 2 years.
High-risk (HR) non-muscle invasive bladder cancer (NMIBC) is defined as carcinoma in situ (CIS), T1 tumor and/or high grade Ta tumor. The CR rate from TURBT and intravesical BCG is approximately 70%, however, a significant percentage of patients with high risk disease experience a recurrence and progression risk is 30-40% over a 10-year period. This is a single arm open-label Phase II study of pembrolizumab (MK-3475) 200mg IV every 3 weeks in patients unresponsive to BCG who refuse or are ineligible for cystectomy. Due to some of the remarkable long lasting responses and rapid approval of PD-1/PD-L1 inhibitors in metastatic urothelial cancer, several trials are ongoing to evaluate the impact of these drugs in patients with BCG unresponsive high risk NMIBC. In the absence of novel therapy, these patients ultimately are treated with radical cystectomy which is a potentially morbid operation. Therefore, this trial is the first of many that are ongoing to look at the potential impact of checkpoint inhibitors in localized high-risk urothelial cancer.
Primary Endpoints: In Cohort A, complete response (defined as the absence of high risk NMIBC) up to 3 years is the primary endpoint. In Cohort B, disease-free survival up to 3 years is the primary endpoint. Secondary Endpoints: The duration of response in Cohort A (absence of any disease either high-risk or low-risk NMIBC) along with overall safety/tolerability.
In this trial there was a very low risk of “missing the window of opportunity” for radical cystectomy as no patients progressed to muscle invasive disease and the complications of radical cystectomy were not increased. Although this preliminary data is exciting and establishes safety and efficacy, it may fall short of the bar set by expert consensus suggesting that novel therapies with activity in CIS BCG unresponsive NMIBC should result in an initial 40-50% CR rate at 6 months with a more durable CR of 30% at 12 months. Furthermore, this finding raises several important questions in patients who achieve a CR such as how long should therapy be continued and can the cost be justified especially if treatment continues beyond 12 months? This interim analysis is of interest, but 12-month data are needed.
At ESMO 2018, Dr. De Wit and colleagues presented a 38.8% complete response (CR) rate in 40/103 patients in Cohort A (CIS containing BCG unresponsive high risk NMIBC) at 3 months among 103 patients. The median time to CR was 12.4 weeks and 80% had a CR duration of greater than or equal to 6 months. However, 25% of patients experienced recurrent NMIBC after CR. No patient developed muscle-invasive or metastatic bladder cancer.