Chronic myeloid leukemia (CML) is a disease that originates from a hematopoietic stem cell characterized by a reciprocal chromosomal translocation t(9;22) (q34;q11). This chromosomal translocation, also known as Philadelphia (Ph) chromosome, is responsible for the formation of the fusion gene BCR-ABL. This chimeric gene codes for a cytoplasmic protein with constitutive tyrosine-kinase activity that has a fundamental role in the leukemogenic process. Imatinib Mesylate shows good rates of haematologic remission, cytogenetic remission and good molecular response. Objective: To compare the major molecular remission (MMR) rate of early versus late imatinib therapy (initiation of imatinib therapy before or after 1 year from diagnosis) in patients with chronic myeloid leukemia (CML) in chronic phase. Methods: Between May 2002 and November 2007, 44 patients with CML in chronic phase were treated with second-line imatinib therapy at the Hematology Service of the Ophir Loyola Hospital in Belem, Brazil. The BCR-ABL transcript levels were measured at approximately 6 months intervals using the real-time quantitative polymerase chain reaction technique. Results: The early treatment group presented a probability of 60% of achieving MMR, while the probability for those that received the late treatment was 40%. The probability of not achieving MMR within 1 year of the initiation of imatinib therapy or loosing MMR was higher in patients that received the late treatment (79%), compared with patients who received early treatment (21%, odds ratio=5.75, P=0.012). The probabilities of maintaining MMR at 30 months of treatment were 80% in the early treatment group, and 44% in the late treatment group (P=0.0005). Conclusion: In patients with CML in chronic phase treated with second-line imatinib therapy, the probability of achieving and maintaining MMR were higher in patients that received an early treatment approach compared with those in whom the time interval between the diagnosis of CML and the initiation of imatinib therapy was longer than 1 year.
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