Nivolumab in Combination With Metronomic Chemotherapy in Paediatrics Refractory / Relapsing Solid Tumors

The study is a two-stage trial: 1. First stage (closed - 16 patients recruited in France): Phase I feasibility trial to evaluate the safety of the combination of Nivolumab + metronomic chemotherapy considering three possible metronomic chemotherapy regimens 2. Second stage (opened - 86 patients expected in France and Belgium): Phase II randomized controlled balanced 1:1 open-label trial comparing the efficacy of the metronomic chemotherapy regimen selected at the end of the previous stage (arm C: cyclophosphamide, capecitabine, vinblastine), with or without nivolumab. 3. "Trans-MetroPD1" ancillary sub-study is partially implemented since April 2022, and proposed to patients participating to second stage