Prognostic and predictive value of an immune-related adverse event among stage III melanoma patients included in the EORTC 1325/KEYNOTE-054 pembrolizumab versus placebo trial.

2517 Background: Several studies suggested that patients (pts) with an immune-related adverse event (irAE) during immunotherapy have better outcomes than those without. It remains uncertain whether these observations can be explained by guarantee-time bias or the role of irAE as an indicator of drug activity. Here, we investigated the association between irAEs and recurrence-free survival (RFS) in the double-blind EORTC 1325/KEYNOTE-054 trial that compared pembrolizumab and placebo in high-risk stage III melanoma pts. Methods: Eligible pts included adults with complete resection of cutaneous melanoma metastatic to lymph node(s), classified as stage IIIA (lymph node metastasis > 1 mm), IIIB or IIIC (without in-transit metastasis) and with no active autoimmune disease that required systemic treatment in past 2 years. We used a Cox model adjusted for sex, age, and stage with a time-varying covariate taking a value zero before the irAE onset and a value one afterwards to estimate the association between the occurrence of irAEs and RFS. Results: Consistent with the main analysis in the ITT population (n = 1019, Eggermont et al, NEJM, 2018), RFS was longer in the pembrolizumab than in the placebo arm (HR = 0.56, 98.4% CI: 0.43-074) among pts who started the treatment (n = 1011). The incidence of irAE on study was 37.3% in the pembrolizumab (n = 509) and 9.0% in the placebo arm (n = 502) and, in each treatment group, it was similar in males and females. The occurrence of an irAE was significantly associated with a longer RFS in the pembrolizumab arm (HR = 0.61, 95% CI: 0.39-0.95, P = 0.03). This was true for both males and females. However, in the placebo arm, no association was observed (HR = 1.39, 95% CI: 0.83-2.32, P = 0.21). Compared to the placebo arm, the reduction in the hazard of recurrence or death in the pembrolizumab arm was greater (P = 0.028) after an onset of an irAE (HR = 0.37, 95% CI: 0.24-0.57) than without/before an irAE (HR = 0.61, 95% CI: 0.49-0.77). Conclusions: In the EORTC 1325/KEYNOTE-054 study conducted in high-risk stage III melanoma pts, the occurrence of an irAE was strongly associated with a longer RFS in those treated with pembrolizumab, but not with placebo. Clinical trial information: NCT02362594.