Prospective study of thromboembolism in 1038 children with acute lymphoblastic leukemia: a Nordic Society of Pediatric Hematology and Oncology (NOPHO) study

Children with acute lymphoblastic leukemia (ALL) are at risk of thromboembolism (TE). This is a prospective evaluation of the incidence, risk factors and outcomes of TE in 1038 children with ALL. TE occurred in 6.1% of children, with the highest incidence (20.5%) among those aged 15-17 years. A TE-associated case fatality of 6.4% indicates that TE is a severe complication of ALL treatment. Summary Background Thromboembolism (TE) is a major toxicity in children with acute lymphoblastic leukemia (ALL) and may have a negative impact on ALL treatment. Objectives To examine the cumulative incidence, outcomes and risk factors associated with TE in children with leukemia. Patients/Methods We prospectively evaluated TE in 1038 Nordic children and adolescents ( 1 and < 18 years) diagnosed with ALL during 2008-2013 and treated according to the NOPHO (Nordic Society of Pediatric Hematology and Oncology)-ALL 2008 protocol. The cohort was followed until December 2014. Cox proportional regression was used to compute hazard ratios (HRs). Results TE events (n = 63) occurred most frequently in conjunction with asparaginase (ASP) administration (52/63). The cumulative incidence of TE was 6.1% (95% confidence interval [CI], 4.8-7.7). Being aged 15-17 years was associated with an increased risk of TE (adjusted HR of 4.0; 95% CI, 2.1-7.7). We found a TE-associated 30-day case fatality of 6.4% (95% CI, 1.8-15.5) and TE-related truncation of ASP therapy in 36.2% (21/58). Major hemorrhage occurred in 3.5% (2/58) of anticoagulated patients. Minor hemorrhage was reported in two out of 58 patients. No major bleeds occurred in children who received low-molecular-weight heparin. Conclusions Methods to identify children and adolescents who will benefit from thromboprophylaxis during ALL treatment are called for. The truncation of ASP should be avoided. The long-term survival outcomes for ALL patients with TE require close monitoring in the future.