Background — There is an elevated risk of venous thromboembolism in patients treated for colon cancer. Postoperative venous thromboembolism has been studied previously, but no large study has compared the risks during different stages of treatment.
Objective — This study aimed to quantify and compare the risks of venous thromboembolism before surgery, after surgery, during adjuvant chemotherapy, and up to 365 days after surgery among patients with resected colon cancer.
Design — This is a population-based retrospective cohort study.
Setting — This study was conducted in a single-payer, universal health care setting (Ontario) between 2002 and 2008.
Patients — A total of 6806 patients with stage I to III colon cancer treated with surgical resection were included.
Interventions — Phases of treatment were evaluated, including preoperative, in-hospital, postoperative, during adjuvant chemotherapy, and 365 days postoperatively.
Main Outcome Measures — Venous thromboembolism, as defined using diagnostic codes from administrative data sources, was the primary outcome measured.
Results — Of the 6806 patients included, 327 (5%) developed venous thromboembolism. Patients receiving adjuvant chemotherapy had a higher risk versus surgery-alone patients (6% vs 4%, p < 0.001). Of the 327 who developed venous thromboembolism, 32% (1.6% overall) were diagnosed during hospital admission and 13.5% (0.6% overall) were diagnosed between discharge and 30 days after surgery. The majority of venous thromboembolisms diagnosed in patients receiving adjuvant chemotherapy (53%, 3.1% of all patients receiving adjuvant chemotherapy) were diagnosed within 180 days of starting adjuvant chemotherapy. Venous thromboembolism was an independent risk factor for worse 5-year overall survival (HR, 1.65; 95% CI, 1.43-1.91; p < 0.001).
Limitations — This study was limited by the potential for misclassification of venous thromboembolism and unknown compliance with prophylaxis recommendations.
Conclusion — Patients who undergo treatment for stage I to III colon cancer are at considerable risk of developing venous thromboembolism. The risk is elevated in those who require adjuvant chemotherapy, and venous thromboembolism is associated with worse long-term outcomes. There may be a role of venous thromboembolism prophylaxis during all phases of treatment, including both after surgery and during adjuvant chemotherapy.