The use of colonoscopy to screen for colorectal cancer may explain the significant decrease in the incidence of that cancer over the past decade. While colonoscopy is now the most common colorectal cancer screening method, evidence has conflicted about how its effectiveness compares with sigmoidoscopy.

Colorectal cancer is the second-leading cause of cancer-related deaths in the United States, according to the Centers for Disease Control and Prevention (CDC). Colorectal cancer screening for people at average risk should begin at age 50 years, according to the American Cancer Society and other groups. Average-risk adults should undergo colonoscopy once every 10 years, and more often if polyps are present.

Colonoscopy and sigmoidoscopy are endoscopic screening methods that are used for early cancer detection and for precancerous polyp removal. Sigmoidoscopy only extends into the lower part of the colorectum, while colonoscopy extends beyond the lower colorectum and into the upper colon. Doctors in the United States have increasingly relied on colonoscopy, and it is the most common method of colon cancer screening. Studies have conflicted about if colonoscopy is superior to sigmoidoscopy, though the thought has been that looking at more of the colon must be better.

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The research team examined available data on the surgery rates for colorectal cancer and interpreted these data in light of the dramatic rise in the use of colonoscopy that began over a decade ago. Data from more than 2 million patients was collected from the Nationwide Inpatient Survey, which includes more than 1,000 hospitals. The researchers looked for trends in colorectal cancer surgery, which reflects cancer incidence. They also looked for differences in rates of cancer in the lower versus upper colon, since colonoscopy should benefit both areas due to its extended reach.

The study’s results suggest that increased use of colonoscopy may explain the decrease in incidence of upper colon cancer in the last decade, since colonoscopy identifies and removes precancerous polyps. The overall rate for resecting lower colorectal cancer dropped from 71.1 to 47.3 per 100,000 persons between 1993 and 1999, and then dropped more steeply, at a rate of 3.8% per year, from 1999 to 2009. In contrast, the resection rate for upper colon cancer remained steady until 2002, and then began to drop at a rate of 3.1% per year until 2009.

These results support the concept that the drop in the incidence of lower colorectal cancer might be associated with screening in general, since some patients were already undergoing stool tests and sigmoidoscopy in the early 1990s, while the reduction in upper colon cancer incidence might be specifically associated with colonoscopy.

This study was published in Gastroenterology (2012;143(5):1227-1236).