Abstract Background Nivolumab obtained approval in advanced melanoma (AM) with weight‐adjusted dose (WAD) administration (3 mg/kg/2 weeks). In 2018, the dosage regimen was changed to flat dose (FD) administration (240 mg/2 weeks or 480 mg/4 weeks) based on a modeling study, without clinical data. Methods AM patients have been prospectively included in the French national multicenter MelBase database since 2013. First‐line patients treated with nivolumab monotherapy were included in the WAD or FD groups of this study. The primary end point was the incidence of grade ≥3 immune‐related adverse events (irAEs). Secondary end points were incidence of any grade irAEs, and overall survival (OS) and progression‐free survival (PFS). Inverse probability of treatment weighting was used to balance groups on their baseline characteristics. Results Between 2015 and 2022, 348 patients were included: 160 in the WAD and 188 in the FD groups. In the FD group, 45% and 27% of patients weighed &lt;75 kg and &gt;85 kg, respectively. Grade ≥3 and any grade irAEs rates were 13.1% versus 11.7% ( p = .8) and 63.1% versus 67.0% ( p = .5) in the WAD and FD groups, respectively. After weighting, median PFS was 3.1 and 3.7 months (hazard ratio [HR], 0.84; 95% confidence interval [CI], 0.65–1.07), and median OS was 24.8 and 37.0 months (HR, 0.74; 95% CI, 0.54–1.01) in the WAD and FD groups, respectively. Conclusions There was no difference in the incidence of severe irAEs and in median PFS between AM patients treated by WAD or FD nivolumab. The median OS between patient groups did not reach statistical significance.

Methods of nivolumab administration in advanced melanoma: A comparison of patients’ clinical outcomes treated with flat dose or weight‐adjusted dose, a multicenter observational study