A 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 Studies

Substudy A: Inclusion Criteria: * Patients must have histologically and/or cytologically confirmed solid tumour, that is advanced/ metastatic/recurrent or unresectable and for which no curative therapy exists. * Patients must live within Canada and have received durvalumab alone, or durvalumab in combination with tremelimumab, with or without chemotherapy/targeted therapy. Patients who have received other anti PD-1/PD-L1 agents +/- anti CTLA agents are eligible, providing full details of prior therapy, toxicity and management are available. Consult with CCTG for further details. * Patients must have previously discontinued immunotherapy due to an irAE. * Immune-related adverse events must have resolved to ≤ grade 1 or baseline and patient must have completed corticosteroid therapy at least 28 days prior to registration in this current study. * Complete response, partial response or prolonged stable disease (SD ≥ 8 weeks) to initial immunotherapy. Patients that received prior adjuvant/neoadjuvant/consolidation immunotherapy are eligible providing there has been at least a 6 month treatment free interval prior to enrollment and patient has received at least one standard-of-care chemotherapy regimen in the palliative setting (discuss with CCTG if chemotherapy is not considered standard of care or not indicated or patient refused/not eligible as such patients are eligible). * Patients must have a life expectancy of at least 12 weeks. * Tumour material may have already been submi…