Natural history of cancer-associated splanchnic vein thrombosis

Background: There is uncertainty in the management of cancer -associated isolated splanchnic vein thrombosis (SpVT). Objectives: To describe the natural history of SpVT by cancer type and thrombus composition and to review anticoagulation (AC) practices and associated rates of usualsite venous thromboembolism (VTE), major and clinically relevant nonmajor bleeding (MB/CRNMB), recanalization/progression, and mortality. Methods: We performed a retrospective cohort study in patients with SpVT at 2 cancer care centers in Houston, Texas. We estimated the incidence of usual -site VTE and MB/ CRNMB at 6 months using competing risk methods and examined venous patency in a subset of patients with repeat imaging. We assessed associations with mortality using Cox regression. Results: Among 15 342 patients with an incident cancer diagnosis from 2011 to 2020, we identi fied 298 with isolated SpVT. Patients with hepatocellular carcinoma (HCC) and SpVT ( n = 146) had the highest disease prevalence (20%), lowest rate of AC treatment (2%), and similar rate of usual -site VTE (4.2%) vs those without SpVT (5.2%) at 6 months, though tumor thrombus vs bland was associated with worse overall survival. In patients with non-HCC bland SpVT ( n = 114), AC ( n = 37) was more common in those with non -upper gastrointestinal cancers and fewer comorbidities. AC was associated with more recanalization (44% vs 15%, P = .041) but no differences in usualsite VTE, MB/CRNMB, or mortality at 6 months. Conclusion: Cancer -associated isolated SpVT is a common but heterogeneous thrombotic disease that is treated differently from usual -site VTE. Tumor thrombus is a negative prognostic factor. Initiation of AC in bland thrombi requires judicious consideration of thrombotic and bleeding risk.