• Biopsy proven relapsed or refractory CD20 positive, grade 1-3a follicular lymphoma (biopsy within 3 months of trial entry)

• Aged 18 years or over

• Advanced disease that in the opinion of the treating physician requires treatment

• Patient suitable for standard available therapy at the Investigator's discretion

• Prior therapy with at least one line of immunochemotherapy. Previous radiotherapy at any time is permitted and will not count as a line of therapy. Previous rituximab monotherapy is also permitted as long as patients have at any time also received at least one line of immunochemotherapy

• Assessable disease by PET-CT (at least one involved node with long diameter \>1.5cm, or extranodal lesion \>1cm )

• ECOG performance status of 0, 1 or 2 at trial entry

• Adequate organ function defined as; i. ANC ≥ 1.0 x 109/L (growth factor use is permitted) ii. Platelet count ≥ 75 x 109/L, or ≥ 50 x 109/L if bone marrow infiltration or splenomegaly iii. ALT and AST level ≤3 x ULN iv. Direct bilirubin level ≤ 2 x ULN, unless due to Gilbert's syndrome v. CrCl ≥ 50mL/min (by Cockcroft-Gault formula) vi. PT, INR and aPTT ≤ 1.5 x ULN, unless receiving anticoagulation vii. LVEF within normal limits by MUGA or echocardiography

• Able to provide written informed consent

⁃ Women of childbearing potential (or their partners) must use an effective form of contraception