Prevention of BC by more effective treatment in early CP as shown by the cumulative incidence of blast crisis (German CML Study Group experience 1983-2011). CML study I compared busulfan versus hydroxyurea (HU) versus interferon-α (IFN) monotherapy, CML study II IFN in combination with HU versus HU alone, CML study III and IIIA IFN in combination with intensive chemotherapy versus allo-SCT and CML study IV imatinib 400 mg versus imatinib in combination with low-dose cytosine arabinoside versus imatinib in combination with IFN versus imatinib after IFN failure versus imatinib at 800 mg.⁴²