INCA is a multicentre, randomised, phase II trial comparing IO-R-CVP with Gem-R-CVP in the first line treatment of patients with DLBCL who are not fit for anthracycline-containing chemotherapy. 132 patients will be randomised to receive either IO-R-CVP or Gem-R-CVP. Samples collected for trial: 7ml EDTA blood sample taken at baseline; Formalin fixed paraffin embedded tumour block - both sent to HMDS, Leeds. Blood serum sample (4.9ml) taken at Baseline (between day -14 pre registration and day 1 pre-treatment), Cycle 1 day 3 (+/- 1 day), Cycle 1 day 8 (+/-1 day) and Cycle 2 day 1 (-1 day) to be sent to Cancer Research UK Manchester Institute, Macclesfield.