Imatinib (IM) has greatly improved survival rates in chronic myeloid leukemia (CML). However, all patients (pts) must continue treatment for an unknown period of time. A pilot study of the first pts who discontinued IM therapy was previously reported (

Rousselot et al. Blood.
). The new, multicentre « Stop Imatinib » (STIM) study was started in July 2007. The aim of this study is to evaluate in a larger cohort the persistence of complete molecular remission (CMR) after stopping IM, and to determine the factors that could influence the persistence of CMR. The criteria for inclusion were IM treatment for at least 3 years and sustained CMR. Sustained CMR was defined as BCR-ABL/ABL levels below a detection threshold corresponding to a 5-log reduction (undetectable signal using RQ-PCR) for at least 2 years. Molecular relapse, defined as RQ-PCR positivity, was taken into account if confirmed in two successive assessments. In cases of molecular relapse, pts were re-treated with IM at 400 mg dailyIn the pilot study, 7 out of 15 pts relapsed within 6 months, but CMR was re-attained in all cases after IM was re-started. The other 8 pts (4 male, 4 female) are still in CMR, with a median follow up of 37 months (range 26–49 months) after IM discontinuation. All pts were pre-treated with interferon-alpha (IFN) and most responded to IFN before IM treatment. The STIM study included 50 pts from 18 centres (20 male, 30 female), with a median age of 62 years (range 32–81 years). Of these, 25 pts had received no pre-treatment with IFN. By July 2008, 34 pts had a follow up ≥ 6 months. Eighteen pts relapsed within the first 6 months: 3 pts in month 2 (M2), 8 pts in M3, 4 pts in M4, and 3 pts in M5. One patient relapsed after more than 6 months (M8). Among the 19 pts who relapsed, 11 were not IFN pre-treated and 8 were IFN pre-treated (relapse rate 44% vs 32%). Ten IFN pre-treated pts with follow up ≥ 6 months have not relapsed (M12 in 2 pts, M10 in 5 pts, M8 in 1 pt, M7 in 2 pts), and 5 pts with follow up ≥ 6 months who were not IFN pre-treated have not relapsed (M12 in 1 pt, M10 in 1 pt), M8 in 1 pt, M6 in 2 pts).

These studies confirm that CMR can be sustained after discontinuation of IM, particularly in pts pre-treated with IFN with a long follow-up (pilot study). Among pts in the STIM study who were not pre-treated with IFN, more than half have not relapsed, and 20% have reached a follow-up ≥ 6 months and not relapsed. Updated data will be presented but we conclude that it is possible to stop treatment in pts with sustained CMR, even in those treated with IM as a single agent.

Disclosures: Off Label Use: Imatinib for treatment of Chronic myeloid leukemia.

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