Abstract Background Retinal vein thrombosis has in case reports been reported a clinical sign of cancer, especially hematological cancer. However, it is unclear whether retinal vein thrombosis is a marker of underlying cancer, as is the case for deep venous thrombosis and pulmonary embolism. We investigated the risk of occult cancer in patients with retinal vein thrombosis. Methods A nationwide population‐based cohort study in Denmark on all patients diagnosed with a retinal vein thrombosis during 1994 and 2013. The main outcome measures were any cancer and site‐specific cancers <6 months, 6‐12 months, and 5 years following a retinal vein thrombosis diagnosis, as registered in the Danish Cancer Registry and the National Pathology Registry. We calculated the absolute cancer risk and computed standardized incidence ratios (SIRs) with 95% confidence intervals (CIs) for cancer within <6 months, 6‐12 months, and 5 years following a retinal vein thrombosis diagnosis. Results Among 9589 patients with retinal vein thrombosis, we observed 1514 cancer cases. The risk of any cancer was 1.2% <6 months and 28.8% after 5 years. The <6 months SIR was 1.20 (95% CI 0.99‐1.44), 6‐12 months SIR was 1.15 (95% CI 0.94‐1.39), and the 5 years’ SIR was 1.08 (95% CI 1.03‐1.14). Stratification by age, gender, calendar year, and Charlson Comorbidity Index score did not change overall cancer risk estimates. Conclusion Retinal vein thrombosis was not an important clinical marker for occult cancer. An extensive diagnostic cancer workup does not appear warranted for retinal vein thrombosis patients
