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Early response after induction is a prognostic factor for disease outcome in childhood acute myeloid leukaemia (AML). Residual disease (RD) detection by multiparameter flow cytometry (MFC) was performed at day 15 and before consolidation therapy in 101 patients enrolled in the Nordic Society of Paediatric Haemato-Oncology AML 2004 study. A multicentre laboratory approach to RD analysis was used. Event-free survival (EFS) and overall survival (OS) was significantly different in patients with and without RD at both time points, using a 0·1% RD cut-off level. RD-negative and -positive patients after first induction showed a 5-year EFS of 65 ± 7% and 22 ± 7%, respectively (P < 0·001) and an OS of 77 ± 6% (P = 0·025) and 51 ± 8%. RD-negative and -positive patients at start of consolidation therapy had a 5-year EFS of 57 ± 7% and 11 ± 7%, respectively (P < 0·001) and an OS of 78 ± 6% and 28 ± 11%) (P < 0·001). In multivariate analysis only RD was significantly correlated with survival. RD before consolidation therapy was the strongest independent prognostic factor for EFS [hazard ratio (HR):5·0; 95% confidence interval (CI):1·9-13·3] and OS (HR:7·0; 95%CI:2·0-24·5). In conclusion, RD before consolidation therapy identifies patients at high risk of relapse in need of intensified treatment. In addition, RD detection can be performed in a multicentre setting and can be implemented in future trials.

In all, 447 children with acute myeloid leukaemia (AML) have been treated on three consecutive NOPHO studies from July 1984 to December 2001. NOPHO-AML 84 was of moderate intensity with an induction of three courses of cytarabine, 6-thioguanine and doxorubicin followed by four consolidation courses with high-dose cytarabine. The 5-year event-free survival (EFS), disease free survival (DFS) and overall survival (OS) were 29, 37 and 38%. NOPHO-AML 88 was of high intensity with the addition of etoposide and mitoxantrone in selected courses during induction and consolidation. The interval between the induction courses should be as short as possible, that is, time intensity was introduced. The 5-year EFS, DFS and OS were 41, 48 and 46%. In NOPHO-AML 93, the treatment was stratified according to response to first induction course. The protocol utilised the same induction blocks as NOPHO-AML 88, but after the first block, children with a hypoplastic, nonleukaemic bone marrow were allowed to recover before the second block. Consolidation was identical with NOPHO-AML 88. The 5-year EFS, DFS and OS in NOPHO-AML 93 were 48, 52 and 65%. The new NOPHO-AML protocol has been based on experiences from previous protocols with stratification of patients with regard to in vivo response and specific cytogenetic aberrations.