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

"* Experimentals Arm A or C (First stage): 2 mg/m2/day IV, weekly per cycle, 28 days cycle~* Experimental Arms Metronomic or Metronomic+Nivolumab (second stage): see C"

"* Arm A (First stage): 30 mg/m2/day PO, D1-4// D8-11// D15-18// D22-25 per cycle, 28 days cycle~* Arm C (First stage): 30 mg/m2/day PO, D1-D4// D15-D18 per cycle, 28 days cycle~* Metronomic or Metronomic+Nivolumab Arm (second stage): see C"

"* Arm B (First stage): 400 to 600 mg/m2/day PO, all days per cycle, 28 days cycle~* Arm C (First stage): 400 to 600 mg/m2/day PO, D8-D11// D22-D25 per cycle, 28 days cycle~* Metronomic or Metronomic+Nivolumab Arm (second stage): see C"

"* Arm A, B or C (First stage): 3 mg/kg IV, D1 \& D15 per cycle, 28 days cycle~* Metronomic+Nivolumab Arm (second stage): 3 mg/kg IV, D1 \& D15 per cycle, 28 days cycle"