Splanchnic venous thrombosis is a marker of cancer and a prognostic factor for cancer survival.

It is unknown if splanchnic venous thrombosis (SVT) is a marker of occult cancer and a prognostic factor for cancer survival. Using Danish medical registries, we conducted a nationwide cohort study including all patients with first-time SVT (n = 1191) between 1994 and 2011. We followed the patients for subsequent cancer diagnoses and calculated absolute risks and standardized incidence ratios (SIRs). We formed a matched comparison cohort of cancer patients without SVT, and assessed the prognostic impact of SVT on cancer survival by applying the Kaplan-Meier method and Cox regression. We followed the patients for a median of 1.6 years, and found that SVT was a marker of occult cancer. The 3-month cancer risk was 8.0% and the SIR was 33 (95% confidence interval, 27-40), compared with the general population. Increased risk was mainly found for liver cancer (risk = 3.5%; SIR = 1805), pancreatic cancer (risk = 1.5%; SIR = 256), and myeloproliferative neoplasms (risk = 0.7%; SIR = 764). The overall SIR remained increased twofold after 1 or more years of follow-up. SVT was also a prognostic factor for survival in patients with liver and pancreatic cancer. The clinical impact may be a more thorough diagnostic work-up in patients presenting with SVT.