 Interferon is the standard treatment of CML before the era of TKI. As a single agent, it induces complete cytogenetic response CCR in about 20, and non-sustainable deep MR in about 10 of patients in early chronic phase. These are much smaller figures compared to TKI. Imatinib at the dose of 400mg daily induces CCR in about 70 and deep MR in about 10 of patient in chronic phase after one year of treatment. However, interferon-responded patients may indeed retain the response once interferon was withdrawn via interferon-induced immunity towards the leukemic clone, which leads to longer drug free period compared to TKI. Hence, it is logical to postulate the use of interferon after TKI was stopped when patients have attained deep MR for more than two years will increase the percentage of patients remain TKI-free on follow-up. Unfortunately, there are not many studies concerning this matter. Carella et al described a case series of five patients with deep MR ranging from 12 to 41 months, were put on interferon with follow-up ranging from three to 16 months. Recently, there was a study from Japan, nine out of 12 analyzable patients including 3 patients with previous treatment of interferon, who stopped TKI, was put on interferon remained in deep MR after median follow-up of 23 months 6-27 months. In regards to peginterferon, there is a small studies by Hardan I et al describing 11 CML patients with various responses after imatinib from complete cytogenetic response N3, major molecular response N6, deep MR N2 were put on peginterferon-α-2a for nine months together with imatinib, then imatinib was stopped and continued with peginterferon-α-2a for another three months. It is difficult to draw any conclusion from this paper because of the small number of subjects, only two subjects have achieved deep MR with unknown duration before study entry, and peginterferon-α-2a was combined with imatinib for nine months which will cloud the true effect of peginterferon-α-2a after imatinib was stopped. 