Trial schema for treatment protocol and sampling for PD-1 RO and pharmacokinetics. Each cycle lasted 28 days and comprised 2 infusions of nivolumab at a fixed 40 mg dose (NIV40) on days 1 and 15, and lenalidomide (LEN10) at a fixed dose of 10 mg from day 1 to 21. Samples for RO were collected at the following time points: before infusion of nivolumab (baseline PD-1 receptor status), 1 hour after infusion of first dose of nivolumab (peak PD-1 RO), and before infusion of second dose of nivolumab (trough PD-1 RO). For pharmacokinetics, plasma samples were obtained during the first cycle of therapy at the following time points: 1 hour after infusion of first dose of nivolumab (peak drug level), 5 days after infusion, 10 days after infusion, and at 14 days (before infusion of second dose of nivolumab, ie, trough drug level). Patients were re-assessed with FDG-PET 4 weeks after the fourth dose of nivolumab. CR, complete response; PR, partial response; PD, progressive disease.