Screening Prevented Up to Half a Million Colorectal Cancer Cases

The head of this pedunculated polyp is erythematous and consists of adenomatous tissue.

Methods of screening for colorectal cancer are estimated to have prevented between a quarter of a million to a half a million colorectal cancers, according to a study published recently in Cancer.

According to Daniel X. Yang, BS, of Yale University School of Medicine, and colleagues these data show the efficacy of screening for colorectal cancer at a population level.

“Although several factors may account for the observed changes in overall cancer incidence, the most likely reason for the reduction in colorectal cancer rates is the primary prevention of cancers by removal of adenomatous polyps during flexible sigmoidoscopy or colonoscopy,” Yang and colleagues wrote. “Such an ecological statement is support by the marked decline of left-sided cancers beginning in the early 1980s, compared with only a minor decline in right-sided cancers.”

In their study, the researchers looked at colorectal cancer incidence data from 1976 to 2009 collected in the SEER database, and data on screening from 1986 to 2010 from the NCI’s Cancer Trends Progress Report.

“Our study is unique, in that our period of analysis spans over 3 decades, crossing eras of different modalities of colorectal cancer screening,” the researchers wrote. “Moreover, we sought to quantify the impact of screening at the population level by estimating the number of cancers prevented in association with screening.”

Data showed that in 1987 only 34.8% of adults aged 50 or older had received screening with colonoscopy, sigmoidoscopy, or fecal occult blood test. However, by 2010, 66.1% of adults in this group were undergoing screening. Data also show a decline in early- and late-stage colorectal cancers during this time for adults aged older than 50 years; whereas, those younger than 50 saw almost no change in the incidence of colorectal cancer.

In addition, the researchers found that during the last 30 years the incidence of left-sided cancers decreased by 139 per 100,000 adults aged 50 or older to 88 per 100,000. Overall, there was a 37% decline in left-sided cancers, and only a 3% decline in right-sided cancers.

The researchers calculated cancer cases prevented using both a stable incidence approach, where they assumed that the underlying cancer incidence remained constant, and an estimated incidence approach, where the baseline incidence was increased by 0.4% each year. Using the first approach, they estimated that during the last 30 years there was a reduction of about 236,000 cancers; using the second, they estimated a reduction of about 550,000 cases of colorectal cancer prevented.

“Despite the temporal association between increased colorectal cancer screening and a decline in colorectal cancer, there have been other changes, including lifestyle behavioral changes and increased use of nonsteroidal anti-inflammatory drugs, which may account for some of the decline in colorectal cancer incidence,” the researchers wrote. “However, the marked reduction in left-sided colorectal cancers, compared with the stable trend of right-sided cancers is unlikely to be driven by changes in lifestyle.”