Associations between neutrophil recovery time, infections and relapse in pediatric acute myeloid leukemia

Background: Children with acute myeloid leukemia (AML) treated similarly show different toxicity and leukemic responses. We investigated associations between neutrophil recovery time after the first induction course, infection and relapse in children treated according to NOPHO-AML 2004 and DB AML-01. Procedure: Newly diagnosed patients with AML with bone marrow blast <5% between day 15 after the start of the treatment and the start of second induction course, and in complete remission after the second induction course were included (n = 279). Neutrophil recovery time was defined as the time from the start of the course to the last day with absolute neutrophil count <0.5 × 10 ⁹ /l. Linear and Cox regressions were used to investigate associations. Results: Neutrophil recovery time after the first induction course was positively associated with neutrophil recovery time after the remaining courses, and longer neutrophil recovery time (≥25 days) was associated with increased risk of grade 3–4 infections (hazard ratio 1.4, 95% confidence interval [CI], 1.1–1.8). Longer neutrophil recovery time after the first induction (>30 days) was associated with the increased risk of relapse (5-year cumulative incidence: 48% vs. 42%, hazard ratio 1.7, 95% CI, 1.1–2.6) for cases not treated with hematopoietic stem cell transplantation in first complete remission. Conclusion: Longer neutrophil recovery time after the first induction course was associated with grade 3–4 infections and relapse. If confirmed, this knowledge could be incorporated into risk stratification strategies in pediatric AML.