Six-month progression-free survival as the primary endpoint to evaluate the activity of new agents as second-line therapy for advanced urothelial carcinoma.

Objective: Second-line systemic therapy for advanced urothelial carcinoma (UC) has substantial unmet needs, and current agents show dismal activity. Second-line trials of metastatic UC have used response rate (RR) and median progression-free survival (PFS) as primary endpoints, which may not reflect durable benefits. A more robust endpoint to identify signals of durable benefits when investigating new agents in second-line trials may expedite drug development. PFS at 6 months (PFS6) is a candidate endpoint, which may correlate with overall survival (OS) at 12 months (OS12) and may be applicable across cytostatic and cytotoxic agents.

Methods: Ten second-line phase II trials with individual patient outcomes data evaluating chemotherapy or biologics were combined for discovery, followed by external validation in a phase III trial. The relationship between PFS6/RR and OS12 was assessed at the trial level using Pearson correlation and weighted linear regression, and at the individual level using Pearson chi-square test with Yates continuity correction.

Results: In the discovery dataset, a significant correlation was observed between PFS6 and OS12 at the trial (R(2) = 0.55, Pearson correlation = 0.66) and individual levels (82%, Қ = 0.45). Response correlated with OS12 at the individual level less robustly (78%, Қ = 0.36), and the trial level association was not statistically significant (R(2) = 0.16, Pearson correlation = 0.37). The correlation of PFS6 (81%, Қ = 0.44) appeared stronger than the correlation of response (76%, Қ = 0.17) with OS12 in the external validation dataset.

Conclusions: PFS6 is strongly associated with OS12 and appears more optimal than RR to identify active second-line agents for advanced UC.