Patients and Methods: We analyzed the clinical and biologic features of 298 infants and children with primary AML treated on four consecutive institutional clinical trials. The Kaplan-Meier method was used in survival analysis and the Cox proportional-hazards model was used to analyze the effect of potential prognostic factors on event-free survival (+/- 1 SE).

Results: Molecular studies of 152 cases detected 42 with MILL rearrangements. The karyotypes of these 42 revealed the t(9;1 1) (15 cases), abnormalities of chromosomes 10 and I I (nine cases), the t(l 1, 19) (four cases), other abnormalities of 11 q23 (seven cases), and miscellaneous rearrangements (seven cases). Among these 42 patients, the 15 whose leukemic cells carried the t(9;1 1) had a better outcome (66% +/- 15%) than the other 27 (25.9% +/- 11.2%; P =.004). Cases with the t(9;11) were also characterized by M5 AML morphology (21 of 23 cases). Of the 63 patients with M5 AML, the 21 whose leukemic cells demonstrated the t(9;1 1) had a better outcome (71.1 % +/- 11%) than the other 42 (25.8% +/- 7.9%, P =.0004). The only independent factors indicating a favorable prognosis were presenting leukocyte count less than 50 x 10(9)/L (relative risk of relapse, 0.73, 95% confidence interval, 0.55 to 0.97; P =.03) and the t(9;1 1) (relative risk of relapse, 0.32; 95% confidence interval, 0.16 to 0.64, P =.002).

Conclusion: We conclude that the t(9;1 1) is the most favorable genetic factor for patients with AML treated at our institution. (C) 2002 by American Society of Clinical Oncology.