Risk of Colorectal Cancer in Patients with Acute Myocardial Infarction and Stroke: A Nationwide Cohort Study

BACKGROUND: An association between colorectal cancer and acute myocardial infarction (AMI) and stroke has been suggested, but evidence is conflicting. METHOD: We conducted a population-based cohort study (1978-2010) of the association between AMI/stroke and colorectal cancer by linking nationwide Danish registries. We calculated standardized incidence ratios (SIR) of colorectal cancer after AMI/stroke as the ratios of observed to expected incidence. RESULTS: A total of 297,523 patients with AMI (median age, 69.4 years; 64% men) were followed for a median of 3.1 years (range, 0-33 years) and 4,387 developed colorectal cancer SIR, 1.08; 95% confidence interval (CI), 1.05-1.11; P < 0.001. In the first year of follow-up, the SIR was 1.85 (95% CI, 1.73-1.98; P < 0.001), whereas it was 0.98 (95% CI, 0.95-1.02; P = 0.318) in the second and subsequent years. We followed 246,998 patients with stroke (median age, 72.4 years; 52% men) for a median of 2.9 years (range, 0-33 years) and 3,035 developed colorectal cancer (SIR, 1.04; 95% CI, 1.00-1.07; P = 0.053). In the first year of follow-up, the SIR was 1.42 (95% CI, 1.31-1.53; P < 0.001), whereas it was 0.96 (95% CI, 0.93-1.00; P = 0.072) thereafter. We found no difference between the SIRs for ischemic and hemorrhagic stroke. The increased one-year relative risks for AMI and stroke corresponded to a 0.3% absolute risk. CONCLUSIONS: Our findings reflect detection of occult cancer at the time of the vascular event. The lack of increased risk after one year suggests that an association based on shared risk factors or chronic inflammation is unlikely. IMPACT: In patients with AMI/stroke, the diagnostic workup including screening for colorectal cancer should follow that of the general population.