This study will assess the response in terms of length of survival, detection of minimal disease levels and time until disease worsens in patients with chronic phase CML who are taking nilotinib and pegylated Interferon. Patients will commence taking nilotinib for 3 months, and once tolerated, will simultaneously be treated with injected pegIFN for up to 2 years. Patients can continue taking nilotinib beyond this time providing they are receiving benefit. Options are available for patients to decrease or increase their dose or to switch to another TKI, imatinib, to ensure a balance between drug effectiveness and minimal side effects is achieved.