Treatment Option Overview for CML
Treatment of patients with chronic myelogenous leukemia (CML) is usually initiated when the diagnosis is established, which is done by the presence of an elevated white blood cell (WBC) count, splenomegaly, thrombocytosis, and identification of the BCR/ABL (breakpoint cluster region/Abelson) translocation. The optimal frontline treatment for patients with chronic-phase CML is the subject of active clinical evaluation but involves specific inhibitors of the BCR/ABL tyrosine kinase.
In a randomized trial comparing imatinib mesylate with interferon plus cytarabine, with 5 years' median follow-up, imatinib mesylate induced complete cytogenetic responses in more than 80% of newly diagnosed patients; in addition, the annual rate of progression to accelerated phase or blast crisis dropped from 2% to less than 1% in the fourth year on the imatinib arm.[Level of evidence: 1iiDiii] However, most of these continually responding patients still showed detectable evidence of the BCR/ABL translocation by the most sensitive measurement of reverse transcriptase–polymerase chain reaction (RT–PCR).[3-5] The clinical implication of this finding after 10 years or more is unknown, but these results have changed clinical practice. Although evidence-based survival advantages are unavailable because of crossover in randomized trials, the overall survival rate for all patients at 5 years is 89%, with fewer than 50% of all deaths (4.5%) caused by CML.
Tyrosine kinase inhibitors with greater potency and selectivity than imatinib for BCR/ABL have been evaluated in newly diagnosed patients with CML. In a randomized, prospective study of 846 patients comparing nilotinib with imatinib, the rate of major molecular response at 24 months was 71% and 67% for two-dose schedules of nilotinib and 44% for imatinib (P < .0001 for both comparisons).[Level of evidence: 1iiDiv] Progression to accelerated-phase CML or blast crisis occurred in 17 patients on imatinib (14%), but this progression occurred in only two patients (<1%, P = . 0003) and in five patients (<1.8%, P = .0089), respectively, on two-dose schedules of nilotinib.
Similarly, in a randomized, prospective study of 519 patients comparing dasatinib with imatinib, the rate of major molecular response at 12 months was 46% for dasatinib and 28% for imatinib (P < .0001). The rate of major molecular response at 24 months was 64% for dasatinib and 46% for imatinib (P < .0001).[Level of evidence: 1iiDiv] Progression to accelerated-phase CML or blast crisis occurred in 13 patients (5%) on imatinib and in six patients (2.3%) on dasatinib (not statistically different).
Although one of these two studies showed statistically significant decreased rates of progression to accelerated or blastic phase, which may ultimately translate into improved survival, the follow-up period with nilotinib and dasatinib has not been long enough to detect and confirm this prolonged survival with these agents. The preferred initial treatment for newly diagnosed patients with chronic-phase CML could be any of these specific inhibitors of the BCR/ABL tyrosine kinase.
The only consistently successful curative treatment of CML beyond 10 years' follow-up has been allogeneic bone marrow transplantation (BMT) or stem cell transplantation (SCT). Long-term data beyond 10 years of therapy are available, and most long-term survivors show no evidence of the BCR/ABL translocation by any available test (e.g., cytogenetics, RT–PCR, or fluorescent in situ hybridization [FISH]). Many patients, however, are not eligible for this approach because of age, comorbid conditions, or lack of a suitable donor. In addition, substantial morbidity and mortality result from allogeneic BMT or SCT; a 15% to 30% treatment-related mortality can be expected, depending on whether a donor is related and on the presence of mismatched antigens.
Long-term data are also available for patients treated with interferon alpha.[11-13] Approximately 10% to 20% of these patients have a complete cytogenetic response with no evidence of BCR/ABL translocation by any available test, and the majority of these patients are disease free beyond 10 years. Maintenance of therapy with interferon is required, however, and some patients experience side effects that preclude continued treatment.
Newly diagnosed patients with very high levels of circulating leukocytes (WBC >100,000/mm3) require immediate therapy with imatinib mesylate to avoid cerebrovascular events or death from leukostasis. Leukophoresis and plateletpheresis are sometimes required for an even more emergent reduction of counts.
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