Venous thromboembolism is the most common cause of death in cancer patients with venous thrombosis. Treatment of venous thrombosis is important in cancer patients, as it can have a major impact on prognosis. We report a case of advanced gastric cancer that was discovered owing to pulmonary thromboembolism and describe the treatment for both conditions. Dose reduction criteria of edoxaban are established. Appropriate dose was based on body weight and creatinine clearance; patients with creatinine clearance values slightly exceeding or below 50 are considered to be on the borderline of the dose reduction criteria. This case had borderline value (body weight: 63 kg, creatinine clearance: 46 mL/min). We observed no response after initiating treatment with 30 mg edoxaban; however, pulmonary thrombus disappeared after increasing the dose to 60 mg edoxaban. When selecting an anticoagulation drug in borderline patients with cancer-associated thrombosis, dose increase should be considered if hemorrhage risk is assessed.