Nivolumab for Pediatric and Adult Relapsing/Refractory ALK+, for Evaluation of Response in Patients With Progressive Disease (Cohort 1) or as Consolidative Immunotherapy in Patients in Complete Remission After Relapse (Cohort 2)

Inclusion Criteria: All criteria from I-1 to I-10 are required for all patients, in addition of the cohort-specific criteria I-1. Histologically confirmed evidence of relapsed/refractory ALK+ ALCL. If biopsy could not be performed, relapsed/refractory status should be confirmed by molecular analysis whenever possible (increase of MRD quantitative PCR at 2 consecutive measures qualifying for a significant increase according to the same reference laboratory, with clinical signs and symptoms suggestive of progressing disease). In this case, relapsed/refractory status must be reviewed and confirmed by the international coordinating investigator. I-2. Age at inclusion \> 6 months I-3. No washout needed, but patients must have recovered from acute toxic effects of all prior therapy before enrollment into the study. A short course of steroids is allowed at the beginning of Nivolumab if it is clinical indicated I-4. Adequate organ function: * Peripheral absolute neutrophil count (ANC) ≥750/μL in patients without bone marrow involvement and ≥500/μL in patients with bone marrow involvement (unsupported) * Platelet count ≥75,000/μL in patients without bone marrow involvement and 50 000 in patients with bone marrow involvement (unsupported) * Hemoglobin ≥8.0 g/dL (transfusion is allowed) * Serum creatinine ≤1.5 x upper limit of normal (ULN) for age * Total bilirubin ≤1.5 x ULN in patients without liver involvement and \< 2.5 ULN in patients with liver involvement * Alanine aminotra…