Background: An increased risk of left-sided colon cancer in patients with diverticular disease of the sigmoid colon has been reported. The aim of this study was to investigate to what extent patients with diverticulitis of the sigmoid colon differ in long-term risk of colon cancer compared to patients with diverticulosis of the colon without any clinical signs of diverticulitis.
Methods: A total of 7159 patients (2478 M, 4681 F) discharged with a diagnosis of diverticulosis or diverticulitis in 1965-83 in the Uppsala Health Care Region were followed-up with the Swedish Cancer Registry. Sixty-four cases with colon cancer were identified and compared with 123 controls without cancer matched for sex, age and year of first discharge. Based on information from the patients' charts, an independent observer blinded to the outcome assigned a clinical diagnosis of diverticulitis or not diverticulitis to cases and controls.
Results: In patients classified as having sigmoid diverticulitis there was an increased risk of left-sided colon cancer compared with patients with diverticulosis without any clinical signs of diverticulitis (odds ratio = 4.2, 95% CI 1.3-13.0) which remained after mutually adjusting for several clinical parameters in a multivariate conditional logistic regression analysis.
Conclusion: The results of the study indicate a causal association between sigmoid diverticulitis and a long-term increased risk of left-sided colon cancer.