A Retrospective Cohort Study of Risk Factors for Symptomatic Venous Thromboembolism in Children and Adolescents With Lymphomas, Prognostic Tool Development, and Internal Prospective Validation.

Venous thromboembolism (VTE) is a significant complication in pediatric lymphoma patients, but no validated risk stratification tool exists. In this single-center cohort study, patients aged 18 years or younger with lymphoma were included. A retrospective cohort (N=262) was analyzed for risk factors for symptomatic VTE (sVTE) and prognostic tool development, while a prospective cohort (N=128) was used for validation. sVTE occurred in 8% of the retrospective cohort. Independent risk factors included: mediastinal tumor volume ≥250 mL (OR=4.42, 95% CI: 1.62-12.7), patient transfer to an intensive care unit due to a life-threatening condition within 30 days of admission (ICU+) (OR=4.27, 95% CI: 1.25-13.9), age 12 years or older (OR=7.43, 95% CI: 2.21-34.6), non-O blood type (OR=5.13, 95% CI: 1.5-24.5). A scoring system assigned points as follows: age 12 years or older (1 point), mediastinal mass ≥250 mL (2 points), ICU+ (2 points), and non-O blood group (1 point). A score ≥2 identified high-risk patients (AUC 0.75, sensitivity 0.75, specificity 0.64). The 1-year cumulative incidence of sVTE was 3.9% (95% CI: 0%-8.2%) in non-high-risk versus 18.3% (95% CI: 7.5%-29.2%) in high-risk groups ( P =0.008). This validated prognostic tool effectively stratifies thrombosis risk and may guide prophylactic strategies in pediatric lymphoma.