Increased risk of left sided colon cancer in patients with diverticular disease.

Certain similar epidemiological characteristics suggest a common aetiology for colon cancer and diverticulosis of the colon. The hypothesis that patients with diverticulosis are at increased risk of developing colon cancer was tested in a retrospective, population based, cohort study in Sweden. A total of 7159 patients (2478 men and 4681 women) who had been given a hospital discharge diagnosis of diverticulosis or diverticulitis of the colon between 1965 and 1983 were followed up during 1985 by means of record linkage procedures. After excluding the first 2 years of follow up, there was not a significant increase in risk (SIR) overall for colon cancer (SIR = 1.2; 95% confidence intervals (CI) 0.9, 1.6) or for rectal cancer (SIR = 1.1; 95% CI 0.7, 1.7). The observed number of right sided colon cancers was as expected (SIR = 0.9; 95% CI 0.5, 1.5). In contrast, an increased risk of left sided colon cancer was found both overall (SIR = 1.8; 95% CI 1.1, 2.7) and consistently in men and women as well as in different age groups. This risk increased the longer the follow up (p value for trend < 0.001). These results do not support the hypothesis of a common aetiology in diverticular disease and colonic cancer but suggest a causal relationship between diverticular disease and cancer of the left colon.