Variation in the risk of venous thromboembolism in people with colorectal cancer: a population‐based cohort study from England

Summary Background Patients with colorectal cancer are at high risk of developing venous thromboembolism (VTE), and recent international guidelines have advised extended prophylaxis for some of these patients following surgery or during chemotherapy. However, our understanding of which patients are at increased risk, and to what extent, is limited. Objectives To determine absolute and relative rates of VTE among patients with colorectal cancer according to Dukes stage, surgical intervention, and chemotherapy. Methods We analyzed data from four linked databases from 1997 to 2006: the Clinical Practice Research Datalink, linked to Hospital Episode Statistics, Cancer Registry data, and Office for National Statistics cause of death data, all from England. Rates were compared by the use of Cox regression. Results There were 10 309 patients with colorectal cancer, and 555 developed VTE (5.4%). The incidence varied by Dukes stage, being three‐fold higher among Dukes D patients than among Dukes A patients (hazard ratio [HR] 3.08, 95% confidence interval [CI] 1.95–4.84), and 40% higher for those receiving chemotherapy than for those not receiving chemotherapy (HR 1.39, 95% CI 1.14–1.69). The risk following surgery varied by stage of disease and chemotherapy, with Dukes A patients having a low incidence of VTE (0.74%; 95% CI 0.28–1.95) at 6 months, with all events occurring within 28 days of surgery, as compared with Dukes B and Dukes C patients, whose risk at 6 months was ~ 2%. Conclusion Twenty‐eight days of prophylaxis following surgery for colorectal cancer is appropriate for Dukes A patients. However, Dukes B and Dukes C patients receiving postoperative chemotherapy have a longer duration of risk.