1. Compared to no screening, flexible sigmoidoscopy decreased the incidence of colorectal cancer and mortality.
2. The benefit was seen in 50-54 year olds, a population that has not been studied in previous trials.
Evidence Rating: 1 (Excellent)
Study Rundown: Colorectal cancer is a leading cause of mortality worldwide and screening by colonoscopy or flexible sigmoidoscopy has been endorsed by many countries as primary prevention. This study was conducted in a large Norwegian population by randomizing participants to either a screening group or a control group (no screening). Within the screening group, participants were further randomized to either once-only flexible sigmoidoscopy or once-only flexible sigmoidoscopy and fecal occult blood testing (FOBT). Participants with a positive screening test were then offered a colonoscopy. The primary outcomes were colorectal cancer incidence and mortality. Compared to the control group (no screening), flexible sigmoidoscopy reduced the incidence and mortality of colorectal cancer by 20% and 27%, respectively. A similar benefit was seen in the 50-54 year old age group. Among the screening group, a one-time FOBT did not improve outcomes beyond sigmoidoscopy alone.
This study is an improvement over similar studies. This was a population-based trial, an improvement over previous trials that relied on volunteers and were conducted in settings in which colonoscopy was available to the control group, which may have attenuated the effects of screening. While current U.S. screening guidelines recommend starting at age 50, previous trials included only those aged 55 or greater; this study included 50-54 year olds. A limitation of this study is that information on deaths was pulled from public registries without additional review. Ultimately, the study emphasizes the importance of screening by colonoscopy in decreasing the incidence and mortality of colorectal cancer.
In-Depth [randomized controlled trial]: Of the 98,792 participants in the intention-to-treat analysis, 78,220 were randomized to the control group and 20,572 were randomized to the screening group. Within the screening group, 10,283 participants were randomized to a flexible sigmoidoscopy and 10,289 were randomized to a flexible sigmoidoscopy and FOBT. Median follow-up time was approximately 10 years in the two groups. Age-standardized colorectal cancer incidence rate was 141.0 in the control group and 112.6 in the screening group per 100,000 person-years, with a hazard ratio of 0.80 (95% CI 0.70-0.92, p=0.001). Age-standardized colorectal cancer mortality rate was 43.1 in the control group and 31.4 in the screening group per 100,000 person-years, with a hazard ratio of 0.73 (95% CI 0.56-0.94, p=0.02). A strong effect of screening was seen in participants in the 50-54 age group; the colorectal cancer incidence hazard ratio was 0.68 (95% CI 0.49-0.94, p=0.02) and mortality hazard ratio was 0.74 (95% CI 0.40-1.35, p=0.32).
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