Objective: To determine the prevalence of occult malignancy in Thai patients with the first episode of unprovoked deep vein
thrombosis, and to identify the methods leading to the diagnosis of occult cancer.

Materials and Methods: The medical records of 369 consecutive patients with symptomatic proximal DVT of the lower extremity were retrospectively reviewed. The patients’ demographic data, sites of occult cancer, and the screening methods utilized for the detection of occult cancer were recorded.

Results: Among the 369 acute DVT patients enrolled in this study, there were 104 (28.2%) unprovoked DVT cases, 106 (28.7%) DVT provoked by transient risk factors, and 159 (43.1%) cancer-associated DVT. Among the 104 patients with unprovoked DVT, occult malignancies were identified in 26 (25%) patients, with 13 (50.0%) of the occult cancers being in the metastatic stage. The methods leading to the diagnosis of occult cancers were limited screening by history taking and physical examination with a routine blood test and chest x-rays in 21 (80.8%) patients, by serum tumor markers screening in 3 (11.5%) patients, and by abdominal computed tomography screening in 2 (7.7%) patients.

Conclusion: The prevalence of occult cancer in acute unprovoked DVT in the present study was 25%, with most of the occult cancers detected by a limited screening strategy.

Keywords: Venous thromboembolism, Unprovoked deep vein thrombosis, Occult malignancy, Cancer-associated deep vein
thrombosis