Incidence of Cancer-Associated Venous Thromboembolism in Patients With Solid Cancers in Japan ― A Prospective Study ―

BACKGROUND: Data on asymptomatic deep vein thrombosis (DVT) remain limited. This prospective study investigated the incidence of cancer-associated venous thromboembolism (CA-VTE) in patients receiving cancer treatment with scheduled DVT monitoring. METHODS AND RESULTS: Patients with newly diagnosed locally advanced, recurrent, or metastatic solid cancers without prior VTE were enrolled. Mandatory baseline venous ultrasonography excluded pre-existing DVT. VTE was assessed at Weeks 12, 24, 36, 48, 72, and 96 by lower-extremity ultrasonography, supplemented by contrast-enhanced computed tomography. The primary endpoint was the incidence of CA-VTE within 24 weeks, and a key secondary endpoint was the incidence within 96 weeks. Cox proportional hazards regression was used to explore factors predictive of newly developed VTE. Among 178 patients (median age 68 years; 32% female), the most common primary site of cancer was the gastrointestinal tract (38%). Adenocarcinoma and squamous cell carcinoma each accounted for 43% of enrolled cases. VTE occurred in 23 (12.9%) and 36 (20.2%) patients within 24 and 96 weeks, with most being asymptomatic (91.3% and 69.4%, respectively). CA-VTE incidence did not differ by tumor site or histology, and no predictive factors were identified. Eleven patients required anticoagulation at VTE diagnosis, and 3 further patients required anticoagulation after progression of initially asymptomatic distal DVT. CONCLUSIONS: CA-VTE incidence was alarmingly high, regardless of tumor site or histology. Because anticoagulation was required in a considerable proportion of patients who developed VTE, scheduled DVT monitoring may be warranted.