Effect of screening colonoscopy on colorectal cancer incidence and mortality

Colonoscopy is used widely for colorectal cancer (CRC) screening; however, its long-term impact on the incidence and mortality of CRC is not known.

We assessed CRC incidence and mortality in a group of asymptomatic average-risk patients who underwent screening colonoscopy between 1989 and 1993 at a university hospital. By using standardized incidence ratios and standardized mortality ratios, we compared our observed CRC rates with expected rates from the Surveillance, Epidemiology, and End Results (SEER) data.

The cohort comprised 715 patients (mean age, 61 +/- 6.5 y; 59% male; 95% Caucasian) with 10,492 patient-years of follow-up. There were 12 cases of CRC: 5 found at baseline and 7 found after a median follow-up period of 8 years (range, 3-16 y). When the first 2 years of follow-up were excluded, there were 7 incident cases of CRC (95% confidence interval [CI], 2-13) over 9075 person-years of follow-up. The expected number based on SEER data was 21. The incidence rate was 0.77 cases per 1000 person-years, and the standardized incidence ratio was 0.33 (95% CI, 0.10-0.62), consistent with a relative risk reduction in CRC incidence of 67%. Three patients died from CRC (95% CI, 0-9). The expected number of deaths based on SEER data was 9. The mortality rate was 0.29 per 1000 person-years, and the standardized mortality ratio was 0.35 (95% CI, 0.0-1.06), consistent with a relative reduction in CRC death of 65%.

In this average-risk cohort, CRC incidence and mortality were reduced after screening colonoscopy. These results provide additional evidence for the effectiveness of colonoscopy as a primary CRC screening modality.