1. Among average-risk adults, negative findings of a screening colonoscopy was linked to reduced risk of colorectal cancer and colorectal cancer related-deaths compared to individuals who had never been screened.
2. The risk reduction associated with negative findings at screening was attenuated with time but was still significantly lower at the guideline-recommended 10-year follow-up.
Evidence Rating Level: 2 (Good)
Study Rundown: Colorectal cancer (CRC) screening programs have been well established to reduce cancer-related mortality by finding cancerous and pre-cancerous lesions that may be amenable to curative resection. Current guidelines recommend colorectal cancer screening at 10-year intervals following negative findings of a screening colonoscopy. However, the data supporting this 10-year time interval is limited and the true risk of colorectal cancer and related mortality following a negative screening colonoscopy is unknown. The current study sought to evaluate the risk of CRC and related mortality following a negative screening colonoscopy in average-risk adults compared to those who have never undergone screening. The study found that the risk of CRC and CRC-related mortality were reduced following a negative colonoscopy up to the 12 years of follow-up in the study. The magnitude of reduction decreased with time but was still significantly lower at the 10-year mark currently recommended by guidelines.
The strengths of the study include the large population of average-risk adults undergoing screening colonoscopies and data on cancer and mortality risk with long-term follow-up. The main limitation of the study was the retrospective cohort design with incomplete data on possible confounders including important exposures (smoking, diet) and family history of CRC.
In-Depth [retrospective cohort]: This was a retrospective cohort study of health plan members from Kaiser Permanente Northern California and included adults aged 50-75 years from 1998 to 2015. Patients were included if they had more than one year of continuous health-care coverage, and were excluded if they were higher-than-average-risk for colon cancer. The primary outcome was the hazard ratio for CRC and cancer-related mortality after adjustment for age, sex, race, BMI, and comorbidity.
The study included 1,251,318 patients with a combined 9,339,345 person-years of follow-up. In the unscreened cohort, the rates of CRC ranged from 62.9 per 100,000 person-years (95% CI, 55.7-70.0) in the first year to 224.8 per 100,000 person-years (95% CI, 202.5-247.0) after 12 years. The rates of CRC in the negative colonoscopy group was 16.6 per 100,000 person-years (95% CI, 6.7-26.6) in the first year to a high of 133.2 per 100,000 person-years (95% CI, 70.9-227.8). At the guideline recommended 10-year mark the negative colonoscopy group had a lower risk of CRC (hazard ratio, 0.54; 95%CI, 0.31-0.94) and cancer-related mortality (hazard ratio, 0.12; 95%CI, 0.02-0.82).
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