Late-occurring Venous Thromboembolism in Allogeneic Blood or Marrow Transplant Survivors - a BMTSS-HiGHS2 Risk Model.

BACKGROUND Allogeneic blood or marrow transplant (BMT) recipients are at risk for venous-thromboembolism (VTE) because of high-intensity therapeutic exposures, comorbidities and a pro-inflammatory state due to chronic graft vs. host disease (GvHD). The long-term risk of VTE in allogeneic BMT survivors remains unstudied. METHODS Participants were drawn from the BMT Survivor Study (BMTSS), a retrospective cohort study that included patients who underwent transplantation between 1974 and 2014 and survived ≥2y after BMT. The BMTSS survey collected information on sociodemographics, health behaviors and chronic health conditions along with age at diagnosis. Details regarding primary cancer diagnosis, transplant preparative regimens, type of transplant and stem cell source were obtained from institutional databases and medical records. We analyzed the risk of VTE in 1,554 2y survivors of allogeneic BMT compared to 907 siblings. Using backward variable selection guided by minimizing Akaike's information criterion, we created a prediction model for risk of late-occurring VTE. RESULTS Allogeneic BMT survivors had a 7.3-fold higher risk of VTE compared to siblings (95%CI: 4.69-11.46, p<0.0001). After a median follow-up of 11y (inter-quartile range: 6-18y), and conditional on surviving the first 2y after BMT, the cumulative incidence of late-occurring VTE was 2.4% at 5y, 4.9% at 10y and 7.1% at 20y after BMT. Older age at BMT (hazard ratio [HR]=1.02/y, 95%CI=1.01-1.04, p=0.002), use of immunosuppressive medications (HR=2.28, 95%CI=1.41-3.38, p=0.0008), obesity (HR=1.06/unit increase in body mass index, 95%CI=1.02-1.10, p=0.002), history of stroke (HR=3.71, 95%CI=1.66-8.27, p=0.001), chronic GvHD (HR=1.62, 95%CI=1.00-2.60, p=0.049), and use of peripheral blood stem cells (PBSCs) as source of stem cells compared to bone marrow (HR=2.73, 95%CI=1.65-4.50, p<0.0001) were associated with increased VTE risk. The final model for VTE risk applied at 2y post-BMT ("HiGHS2") included History of stroke, chronic GvHD, Hypertension, Sex (male vs. female) and Stem cell source (PBSCs vs. other) (corrected C-statistics: 0.73; 95%CI=0.67-0.79), and was able to classify patients at high and low VTE risk (10y cumulative incidence 9.3% vs. 2.4%, p<0.0001). CONCLUSIONS The BMTSS HiGHS2 risk model when applied at 2y post-BMT can be used to inform targeted prevention strategies for patients at high risk for late-occurring VTE.