Patients with advanced melanoma are, amongst others, currently treated with nivolumab monotherapy or with nivolumab and ipilimumab followed by nivolumab. Even though registration studies administered nivolumab in a 3 mg/kg 2 weekly scheme, currently, nivolumab monotherapy is either administered in a 240 mg 2-weekly scheme or in a 6 mg/kg or 480 mg 4-weekly scheme. With the current dosing regimen, steady-state is achieved after approximately 5 to 6 months, whereas a tumour response is usually observed earlier in patients with metastatic melanoma. Moreover, PD-1 receptor occupancy is almost saturated above doses of 0.3 mg/kg, or at nivolumab serum levels of 10 mg/L, which is a concentration that is achieved after one treatment cycle. In melanoma patients, the additional probability on response in patients treated with 3 mg/kg compared to 1 mg/kg seems limited. PFS and OS for 3 mg/kg were not superior to 1 mg/kg. Therefore, in this study, our aim is to investigate nivolumab trough levels and pharmacokinetic parameters after 3 reduced nivolumab doses.