Objective. To study the outcome of children with acute lymphoblastic leukaemia who were treated using a protocol including one or two delayed intensifications. Design. Prospective single-arm multicentre study. Setting. Five designated children cancer units of the Hospital Authority of Hong Kong. Patients. Children aged between 1 and 17.9 years with newly diagnosed acute lymphoblastic leukaemia seen from November 1997 to December 2002. Intervention. Chemotherapy was modified from a German Berlin-Frankfurt-Muenster 95 (BFM95) protocol that included a delayed intensification similar to the induction phase repeated 5 months after diagnosis. High-risk patients were given double delayed intensification. Main outcome measures. Overall survival and event-free survival of the whole group and the three risk groups (standard-, intermediate-, and high-risk groups), and comparison with historical controls. Results. A total of 171 patients were recruited with a median age at diagnosis of 5.57 years (range, 1.15-17.85 years). The induction remission rate was 95.3% and non-leukaemia mortality during remission was 2.3%. At 4 years, the relapse rate of this (HKALL97) study was significantly lower than that of the HKALL93 study (15.7 vs 37.3%; P<0.001). The 4-year overall survival of HKALL97 and HKALL93 studies were 86.5% and 81.8%, respectively (P=0.51). The 4-year event-free survival for HKALL 97 and HKALL93 studies were 79% and 65%, respectively (P=0.007). Nonetheless the difference of event-free survival was most remarkable in the intermediate-risk group: 75.6% and 53.1% for HKALL97 and HKALL93 studies, respectively (P=0.06). Conclusion. A more intensive delayed consolidation phase improved the outcome for children with acute lymphoblastic leukaemia by reducing relapses at 4 years. The early treatment complications were manageable and non-leukaemia mortality during remission remained low.published_or_final_versio
