When to stop immunotherapy for advanced melanoma: Emulation of target trials.

9521 Background: Immune checkpoint inhibitors (ICI) have demonstrated their effectiveness with a 7.5-year overall survival (OS) close to 50% for advanced stages. The design of clinical trials allowed treatment until progression or toxicity, or for a maximum duration of two years. Prolonged follow-up of responders after cessation shows sustained response and a low risk of relapse in the months following cessation. As of yet, the optimal duration of anti-PD-1 therapy for metastatic melanoma remains unestablished. The objective of this work was to evaluate the optimal duration of ICI. Methods: We conducted emulated trials using the cloning, weighting and censoring approach. Each emulated trial aimed at comparing the causal effect of stopping versus continuing ICI at a specific timepoint, in patients still under treatment and with disease control at that time. Results: The study comprised 1017 participants to the MELBASE cohort. Results of the 6-month discontinuation emulated trial showed a significantly lower OS if treatment was discontinued, compared to continuing treatment for at least three months. The 48-month survival difference was 37.8% (95% confidence interval [CI] 19.8 to 60.5), and the corresponding restricted mean survival time difference 8.3 months (95% CI: 4.1 to 12.7). The 12-month and 18-month discontinuation emulated trials both showed no evidence of benefit of either discontinuing or continuing ICI at any of those timepoints. The 24-month discontinuation emulated trial results were more in favor of stopping compared to continuing treatment at that decision point, with an absolute 48-month survival 10.5% higher (95% CI 4.4 to 18.1). Conclusions: These results suggest that a one-year course of immunotherapy is both necessary and sufficient for patients with advanced melanoma. Prolonged treatment beyond 2 years does not appear to be beneficial in terms of survival and could even be detrimental.[Table: see text]