Late-occurring venous thromboembolism in allogeneic blood or marrow transplant survivors: a BMTSS-HiGHS2 risk model.

Allogeneic blood or marrow transplant (BMT) recipients are at risk for venous thromboembolism (VTE) because of high-intensity therapeutic exposures, comorbidities, and a proinflammatory state due to chronic graft-versus-host disease (GVHD). The long-term risk of VTE in allogeneic BMT survivors remains unstudied. Participants were drawn from the Blood or Marrow Transplant Survivor Study (BMTSS), a retrospective cohort study that included patients who underwent transplantation between 1974 and 2014 and survived ≥2 years after BMT. We analyzed the risk of VTE in 1554 2-year survivors of allogeneic BMT compared with 907 siblings. Using backward variable selection guided by minimizing Akaike information criterion, we created a prediction model for risk of late-occurring VTE. Allogeneic BMT survivors had a 7.3-fold higher risk of VTE compared with siblings (95% CI, 4.69-11.46; P < .0001). After a median follow-up of 11 years, conditional on surviving the first 2 years after BMT, the cumulative incidence of late-occurring VTE was 2.4% at 5 years, 4.9% at 10 years, and 7.1% at 20 years after BMT. The final model for VTE risk at 2 years post-BMT included History of stroke, chronic GVHD, Hypertension, Sex (male vs female) and Stem cell source (peripheral blood stem cells vs other) ("HiGHS2") (corrected C-statistics: 0.73; 95% CI = 0.67-0.79). This model was able to classify patients at high and low VTE risk (10-year cumulative incidence, 9.3% vs 2.4% respectively; P < .0001). The BMTSS HiGHS2 risk model when applied at 2 years post-BMT can be used to inform targeted prevention strategies for patients at high risk for late-occurring VTE.