Randomized, Open-label, Two-arms, Phase III Comparative Study Assessing the Role of Involved Mediastinal Radiotherapy After Rituximab Containing Chemotherapy Regimens to Patients With Newly Diagnosed Primary Mediastinal Large B-Cell Lymphoma

Primary mediastinal large B cell lymphoma is treated with a combination of chemotherapy and the monoclonal antibody rituximab (chemoimmunotherapy). Following chemoimmunotherapy patients receive radiation therapy if they have residues which may be active tumour. However at the end of chemoimmunotherapy the majority of patients show tissue scarring that is not necessarily active tumor. In recent years, PET/CT has proved to be a good tool to accurately identify active tumor from scar tissue in patients treated for mediastinal lymphoma.The purpose of this trial is to test whether radiation therapy is really necessary in patients where PET/CT has shown that the tumor is no longer active. Therefore we will compare radiation treatment with careful observation. Patients that at the end of conventional treatment of chemoimmunotherapy have a negative PET/CT (i.e., without residues suspected to contain active tumor), will randomly assigned to two different treatment groups: one treatment group will receive the radiation treatment, and the other treatment group will receive careful observation. The trial is planned according to a non-inferiority design aimed at demonstrating that progression free survival after the experimental treatment (observation) is not worse than after the standard comparator (mediastinal irradiation.Participation in this study could spare patients with complete remission at the end of chemo immunotherapy (PET/CT negative) radiation therapy that may be unnecessary.