LAUSR

There are conflicting data about whether the development of cancer‐associated thrombo‐embolism (TE) negatively impacts survival in children. The objective was to determine whether TE during treatment was associated with overall survival (OS) and event‐free survival (EFS) in children with acute lymphoblastic leukemia (ALL). We performed a population‐based retrospective cohort study using the Cancer in Young People‐Canada registry. Children <15 years of age were diagnosed with de novo ALL (2000–2016). The primary exposure variable was radiologically‐confirmed thrombo‐embolism requiring medical intervention. Multivariable Cox regression models were used to determine the impact of thrombo‐embolism on survival, where TE was time‐dependent. We included 2006 children (median age: 4 years, 88.5% precursor B‐cell ALL). Thrombo‐embolism occurred in 113 patients (5.6%), at a median time of 107 days (interquartile range: 35–184 days) after ALL diagnosis. Among standard/low‐risk patients, 41/1165 (3.5%) developed TE while among high/very high‐risk patients, 72/841 (8.6%) developed TE. Patients with TE had a significantly worse OS (adjusted HR [aHR] of death: 2.61, 95% CI: 1.62–4.22, p < 0.001) and EFS (aHR of an event [death, relapse, second malignancy]: 2.03, 95% CI: 1.35–3.05, p = 0.001), compared with patients without TE. No statistically significant difference was seen in standard/low risk ALL for OS and EFS, but TE was associated with a significantly lower OS and EFS in children with high/very high‐risk ALL (aHR of death: 2.90, 95% CI: 1.79–4.72, p < 0.001; aHR of an event: 2.02, 95% CI: 1.30–3.12, p = 0.002). Thus, TE led to a statistically significant reduction in OS and EFS in children with high risk/very high‐risk leukemia.