DISCUSSION
We evaluated the association between deep venous thrombosis or pulmonary embolism and a subsequent diagnosis of cancer in a large cohort and found an increased risk of several types of cancer, almost entirely during the first year of follow-up. In particular, there was a strong association between thrombosis and cancer of the pancreas, ovary, liver, and brain during the first year. The magnitude of risk was similar to that observed in previous studies. However, the rapid fall in the standardized incidence ratio after six months of follow-up strongly suggests that a thromboembolic event in patients later given a diagnosis of cancer is the result rather than the cause of the cancer. If the thromboembolic event had contributed to causing the cancer, we would have expected an increasing risk with length of follow-up, because of the long latency period for most cancers. If, alternatively, common risk factors for thromboembolism and cancer had been present, we would have expected a constant excess risk over time.