**1. Introduction**

Cancer is one of the leading causes of death in developed countries including Japan. According to the Japanese Cancer Institute registry data, 1,017,200 patients were estimated to be newly diagnosed with cancer, and 380,300 patients were estimated to die from cancer in 2019 [1]. Colon cancer is the most often diagnosed in Japanese people, followed by gastric and lung cancer. Lung cancer most often causes death related to cancer, followed by colon and gastric cancer. Approximately half of Japanese people suffer from cancer during their lifetime, and one-third die from cancer. Venous thromboembolism (VTE) is a common and serious complication in patients with cancer. The risk of VTE in cancer patients is severalfold higher than that in individuals without cancer [2, 3], and VTE is the second leading cause

of death in cancer patients undergoing chemotherapy after death directly related to cancer [4]. Therefore, it is important to prevent and treat cancer-associated VTE to improve prognosis of cancer.
