Statistical Analysis Plan Summary The study employs a one stage phase II Fleming's design using irPFS at 1 year as primary endpoint. Using response hypotheses of H0 < 12 % and Ha> 25% i.e. that the irPFS at 1 year for the maintenance Pembrolizumab arm is 25%, compared to 12% in the normal chemotherapy maintenance arm, with a significance level (i.e., the probability of rejecting H0 when it is true) α=0.05 and the power (i.e. the probability of deciding the regimen is active) is 0.8 when true response rate is 25%, 48 patients are required to be entered into this study.