Pembrolizumab for Previously Treated Advanced or Metastatic Urothelial Cancer: An Evidence Review Group Perspective...

Pembrolizumab is an intravenously administered monoclonal antibody licensed for locally advanced or metastatic urothelial carcinoma after platinum-containing chemotherapy. This summary presents the perspective of Warwick Evidence, the Evidence Review Group (ERG) appointed by the National Institute of Health and Care Excellence (NICE) for the single technology appraisal of pembrolizumab for this indication. Pembrolizumab is manufactured by Merck, Sharp and Dohme (MSD). The major source of clinical effectiveness was the KEYNOTE-045 trial, where 542 patients received either pembrolizumab or clinician's choice of docetaxel, paclitaxel or vinflunine as a second-line treatment. No indirect treatment comparison was performed. The clinical effectiveness was assessed using hazard ratios for overall survival (OS) and progression-free survival (PFS) of the intention-to-treat (ITT) population, together with the subpopulations positive for programmed cell death 1 ligand 1 (PD-L1) expression (combined positive score [CPS] ≥ 1%) and strongly positive for PD-L1 expression (CPS ≥ 10%). In the ITT population, OS improved with pembrolizumab (HR 0.73, 95% CI 0.59-0.91) while PFS outcomes showed no difference (HR 0.98, 95% CI 0.81-1.19). Pembrolizumab demonstrated a better safety profile than its combined comparators, with fewer patients experiencing adverse events (60.9 vs 90.2%). Similar results were observed in populations expressing PD-L1. MSD estimated the cost effectiveness of pembrolizumab using a de novo partitioned survival model. The model had three health states: pre-progression, post-progression and death, where OS and PFS estimates excluded patients who received vinflunine. The largest uncertainty was over the selection of the parametric models used to extrapolate OS and PFS and the time point for when to begin their extrapolation. The company preferences for extrapolation were not well supported and the ERG disagreed with their selection for OS. Utility values were also contentious, with the company preferring to use pooled time-to-death-based utilities pooled across treatment arms, whilst the ERG preferred pooled progression-based utilities. The company preferred to use data from patients receiving vinflunine when calculating the utility values, which the ERG disagreed with as this is not recommended treatment within the UK. The company assumed a lifetime treatment effect for their model; however, the lack of evidence made it difficult to confidently provide a realistic estimate of treatment effect duration. Various durations were explored (3, 5 and 10 years). The first appraisal committee meeting concluded that pembrolizumab was not cost effective, largely due to uncertainty in the OS and PFS extrapolations. The company's second submission included an additional 4 months follow-up to survival data. The company in this new submission maintained their original assumptions in their base-case analysis, changing only the choice of parametric curve for PFS. This change resulted in the OS and PFS curves intersecting at 6 years in the pembrolizumab arm, at which point PFS identically followed OS. This resulted in no patients in the post-progression health state beyond this time point, and therefore, the majority of pembrolizumab's benefit came from pre-progression survival. Given the unclear PFS benefit, the ERG found this implausible and maintained their original base-case model assumptions. Considerable uncertainty remained over the specification of the extrapolations and the duration of treatment effect. Based on a new-value proposition submitted by the company, the appraisal committee concluded that pembrolizumab had plausible potential to be cost effective. Pembrolizumab was referred for funding through the Cancer Drugs Fund, so that further data could be collected with the aim of diminishing the outstanding uncertainties pertaining to its clinical effectiveness.