Background: Although the relationship between deep venous thrombosis (DVT) and malignancy has been recognized for centuries, it is based on epidemiologic and usually retrospective studies of selected patient groups. The prevalence of unrecognized malignancy in primary care patients with DVT is unknown. Oudega and colleagues tried to determine the incidence of occult malignancy in patients with DVT and to identify any patient characteristics that might indicate an elevated risk.

The Study: The study involved 1,829 consecutive patients who consulted primary care physicians between 1996 and 2002 with pain and swelling of one leg lasting for up to 30 days. Diagnosis was confirmed by ultrasonography. If the initial examination was normal, the test was repeated after seven days. Patients with confirmed DVT were treated with low-molecular-weight heparin and vitamin K antagonists until their International Normalized Ratio (INR) reached 2 to 3. Vitamin K antagonist therapy was then continued for three to six months.

Idiopathic DVT was diagnosed if no risk factors (e.g., recent surgery, prolonged immobilization, use of hormones, history of DVT, coagulation disorder) were identified. Patients with primary and secondary DVT were compared in the study results. The study excluded patients with a current or previous malignancy, and those who were diagnosed with malignancy within 14 days of confirmation of DVT. Patients and a comparable control group were followed for two years to establish the incidence of malignancy.

Results: Of the 430 DVT patients, 162 had idiopathic DVT and 268 had secondary DVT. The groups were similar in average age (about 60 years) and other significant variables, but the idiopathic group had a higher proportion of men (41 compared with 36 percent). During the two-year follow-up period, malignancy was diagnosed in 19 DVT patients (4.4 percent) compared with nine control patients (2.0 percent). The incidence was significantly higher for patients with idiopathic DVT than for patients with secondary DVT (7.4 compared with 2.6 percent). Although malignancy was significantly more common in patients with DVT, no single site or type of malignancy was identified as particularly common (see accompanying table).

Conclusion: The authors conclude that primary care patients with idiopathic DVT have about three times the risk of being diagnosed with malignancy within two years compared with control patients. Because of the variety of malignancies detected and the lack of evidence of benefit, no recommendations can currently be made about screening for cancer in patients with DVT.