Similarly, in a randomized, prospective study of 519 patients that compared 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 CML, 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.
Higher doses of imatinib mesylate, alternative tyrosine kinase inhibitors (such as dasatinib or nilotinib, and allogeneic SCT) are implemented for suboptimal response or progression and are under clinical evaluation as frontline approaches.[11,12,13,14,15,16,17,18,19] Currently in practice, dose escalation of imatinib is usually the first step taken for suboptimal response, but clinical trials are required to establish the relative efficacy and sequencing of dose escalation, dasatinib, and nilotinib.[16,17] Two studies looked at dose escalation of imatinib in almost 200 previously untreated patients, most of whom were of intermediate Sokal risk; 63% to 73% achieved a major molecular response by 18 to 24 months and only three patients showed progression to advanced phase in these preliminary phase II results.[20,21][Level of evidence: 3iiiDiv] Until randomized studies are performed, it is unclear whether the increased response with increased dosage will translate into longer durations of response or survival advantages.[18,22]
A single-center, retrospective analysis of 483 patients with chronic phase CML who were treated with imatinib (400 mg or 800 mg daily), dasatinib, or nilotinib, indicated that patients who have better than 35% t(9;22)+ cells at 3 months of therapy have inferior event-free, transformation-free, and OS rates compared with patients who have better early cytogenetic responses.