The BCR-ABL tyrosine kinase inhibitor imatinib mesylate (Gleevec) induces complete cytogenetic responses (CCR) in more than 85% of patients with chronic myelogenous leukemia (CML). However, patients in CCR relapse after imatinib interruption in case of detectable residual disease. In fact, less than 10% of patients achieve a molecular remission, defined by an undetectable residual disease using real time quantitative polymerase chain reaction (RTQ-PCR). We previously reported the outcome of CML patients in CCR after cessation of interferon-alpha during the pre-imatinib era. Seven (all with a negative PCR) out of 15 patients did not relapse (

J Clin. Oncol.
,
20
,
2002
:
214
–220
). In the present study, we address the issue of the discontinuation of imatinib in CML with undetectable residual disease for more than 2 years in 15 patients. The median duration of RTQ-PCR negativity and imatinib therapy were respectively 32 months (24–46) and 45 months (32–56) before imatinib interruption. Eight patients displayed a molecular relapse with a detectable BCR-ABL transcript appearance between the first 6 months. Imatinib was then re-introduced and led to a novel molecular response in most patients. Seven other patients have still an undetectable level of BCR-ABL transcript after a median follow up of 20 months (9–24). With the assumption that the doubling time of a proliferative CML cell is 8 days, it will take a maximum of 6 months if only one leukemic cell persists and proliferates to reach 107 cells i.e corresponding to a residual disease detectable by RTQ-PCR. Relapses observed within 6 months may reflect the kinetic of undetectable dividing CML cells. Those cells may be eradicated or controlled in long term non relapsing patients described in our study.

Topics:
disease remission, follow-up, imatinib mesylate, leukemia, myelocytic, chronic, polymerase chain reaction, bcr-abl tyrosine kinase, residual tumor, interferon-alpha, leukemic cells, neoplasm, residual

Disclosure: No relevant conflicts of interest to declare.

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2006, The American Society of Hematology
2006
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