Brentuximab Vedotin in Early Stage Hodgkin Lymphoma

Eligible patients will be randomised to receive either ABVD chemotherapy (doxorubicin, bleomycin, vinblastine and dacarbazine) or A2VD chemotherapy (doxorubicin, brentuximab vedotin, vinblastine and dacarbazine, with growth factor support). If patients agree, they will have a PET-CT scan after 1 cycle (PET1). The result of this scan will be blinded and used for exploratory endpoints only. Treatment will not be influenced by the result of this scan. All patients will have a PET-CT scan after 2 cycles of treatment (PET2) which will be centrally reviewed. The Deauville score from central review will be used to risk adapt subsequent therapy as follows: * Patients with Deauville score 1-3 will have one further cycle of their randomised chemotherapy and then enter follow up. * Patients with Deauville score 4 will have two further cycles of their randomised chemotherapy followed by involved site radiotherapy * Patients with Deauville score 5 will be withdrawn from trial treatment. They will have further treatment at their treating clinician's discretion and will enter follow up for the trial. Patients with Deauville score 4 on PET2 will have a final PET-CT scan to confirm adequate treatment response. Patients will be followed up for a minimum of 5 years after completing treatment.