Warfarin, Pulmonary Embolism, and Cancer

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To the editor: The recent article by Gore and associates (1) convincingly shows an increased incidence of cancer in patients after acute pulmonary embolism. However, a significant number of their patients (five of 19) developed cancer 3 or more years after the pulmonary embolism. Although the association of thrombosis preceding occult malignancy is well established, a delay of this magnitude might suggest another explanation. The authors' data are also compatible with prolonged anticoagulation of the pulmonary embolus group by warfarin, resulting in cancer. But evidence for a direct carcinogenic role for warfarin is scant; moreover, anticoagulation is widely believed to