An Open Label, Single-arm, Phase 2 Study of Neoadjuvant Pembrolizumab (MK-3475) Before Cystectomy for Patients with Muscle-invasive Urothelial Bladder Cancer

Fondazione IRCCS Istituto Nazionale dei Tumori, Milano
Study Design: 
This is a Phase II, single arm clinical trial of patients with histologically confirmed MIBC (T2-T3bN0), predominant urothelial histology ( 50%), and residual disease after transurethral resection of bladder tumor. Although patients had to have GFR 20 mL/min, researchers were agnostic to cisplatin eligibility and patients were not offered cisplatin. Patients were treated with 3 treatments of 3 weekly treatments of pembrolizumab and then underwent radical cystectomy. Cystectomy specimens underwent genomic sequencing with the Foundation One Assay.
Patients with muscle-invasive bladder cancer (MIBC) are at risk for relapse and poor overall survival due to understaging of disease and micrometastatic disease. Due to poor adoption of neoadjuvant chemotherapy and the lack of an effective non-cisplatin based regimen, this group from Italy sought to investigate the use of neoadjuvant pembrolizumab prior to radical cystectomy for MIBC.
In this interim analysis, the primary endpoint was pathologic complete response (pT0) rate and responses 25% were considered significant. Thirty-six patients were evaluated. The final trial will look at the 2-year overall survival rate in all planned 90 patients.
Overall, the results are very exciting and suggest that neoadjuvant pembrolizumab has activity in this setting and potential biomarkers associated with pT0 responses were identified. Although pT0 rates as high as almost 40% have been associated with neoadjuvant chemotherapy, a meta-analysis of 10 trials suggests that the pT0 rate from chemotherapy is closer to 27.8%.1 Also this trial required residual disease after transurethral resection of the bladder tumor and so the pT0 rate is even more impressive with pembrolizumab. Finally, the association of improved pT0 rates with DDR mutations, PD-L1 expression, and Rb1 mutations foretells a future where we may be able to more intelligently select patients for neoadjuvant therapies. However, there are some concerns with the trial. Four patients on the trial suffered unique complications such as ileal anastomosis dehiscence/fistula or ureteral anastomosis dehiscence. This raises a concern about the nature of potential surgical complications if completing immunotherapy 2-3 weeks before surgery. Nevertheless, this is a novel trial and will probably open the door for a randomized neoadjuvant trial of immunotherapy versus chemotherapy prior to radical cystectomy.
Interim efficacy and an interim biomarker analysis was presented at the AACR meeting. The pT0 rate was 38.9% in all patients (47.4% in those with high PD-L1 expression defined as a combined positive score 23% which measures expression in tumor cells, lymphocytes, and macrophages). The pT0 rate was 60% in those with DNA Damage Repair (DDR) mutations and 100% in those with DDR mutations AND high PD-L1 expression. Mutational analysis demonstrated that Rb1 mutations were associated with pT0 response whereas FGFR3 mutations were associated with a non-pT0 response. Interestingly the median time from the end of pembrolizumab to radical cystectomy was 22 days and only 14 days in the last ten patients. Any grade adverse events were experienced in 47% patients but only 5.6% patients experienced grade 3-4 toxicity.