RecruitingPhase 2Drug trialA Phase II Study of Durvalumab Treatment - Substudy A: In Patients Who Discontinued Prior Checkpoint Therapy Due to Immune Related Toxicity - Substudy B: For Continued Treatment (+/- Tremelimumab) of Patients Previously Enrolled to Completed CCTG StudiesI238A: The purpose of this study is to find out what effects being treated with durvalumab has on cancer. The researchers doing this study also want to evaluate if prednisone (a type of steroid), when given together with durvalumab, can reduce any side effects. I238B: The purpose of this study is to allow patients previously enrolled on a completed CCTG trial to continue treatment with durvalumab (+/- tremelimumab)