Colorectal cancer screening offers chance to prevent the second deadliest cancer
By Andy Koopmans
A recent report by the Centers for Disease Control and Prevention indicated that between 2002 and 2010, the number of Americans getting tested for colorectal cancer rose from 54 to 66 percent. However, the report also noted that 23 million people who fall into the recommended screening age range of 50 to 75 have not been screened, and state-by-state data taken from a 2012 Behavioral Risk Factor Surveillance System survey indicated that testing compliance varies widely by location.
Dr. Polly Newcomb, who heads Fred Hutchinson Cancer Research Center’s Cancer Prevention Program, said that those who aren’t getting tested are unnecessarily putting themselves at risk for one of the deadliest cancers. “Colon cancer is the No. 2 cancer killer of men and women together,” she said, “and, along with cervical cancer, it’s one of only two cancers that can be prevented through early detection of precancerous changes rather than behavior modification, so testing is important.”
The American Cancer Society recommends screening for men and women 50 and over who are at average risk for colorectal disease. People with a personal or family history of colorectal polyps or cancer, inflammatory bowel disease and other risk factors should be screened earlier and more frequently.
Colorectal cancer tests include various visualization techniques, such as sigmoidoscopy and colonoscopy, and stool tests that look for hidden blood in feces that can indicate blood loss anywhere in the digestive tract. Positive fecal screenings typically are followed up by a colonoscopy.
In sigmoidoscopy and colonoscopy, a camera on a flexible tube is passed through the anus into the lower gastrointestinal tract, which allows visual detection of polyps, ulcerations or suspected colorectal cancer lesions, which are removed on the spot and biopsied under a microscope to determine whether they are precancerous or malignant.
Sigmoidoscopy examines the lower portion of the colon (approximately 24 inches in length) whereas a colonoscopy examines the entire colon ( about 47 to 60 inches long). Newcomb indicated that fewer doctors perform sigmoidoscopies because the test leaves so much of the colon unexamined. Instead, most doctors opt for colonoscopy or virtual colonoscopy, a medical imaging procedure that uses X-rays and computer software to produce two- and three-dimensional images of the entire bowel.
According to the CDC report, colonoscopy was the most commonly used screening test for colorectal cancer, with approximately 62 percent of individuals opting for it, whereas fecal testing accounted for about 10 percent of screening. The least common form of screening was a combination of sigmoidoscopy and fecal testing, which accounted for less than 1 percent.
Other forms of colorectal cancer screening are also under development. At Fred Hutch, Newcomb and her colleagues are working on blood tests to detect biomarkers that could determine whether a visual exam is necessary as well as prediction models that look at an individual’s risk factors to determine how frequently screening exams should be done.
Fecal tests and sigmoidoscopies typically are recommended more frequently to patients of screening age than colonoscopies, which are recommended every 10 to 20 years. According to Newcomb, the growth of a precursor lesion into an invasive cancer may take 15 to 20 years. “The growth is so slow that if you get a colonoscopy at 50 and you’re clean, then you might not need another one if you’re not a polyp-former. If you are, you might need to have an additional colonoscopy a year later and a follow-up thereafter every three years,” she said.
“The takeaway is that colon cancer screening is clearly associated with mortality reduction. It’s a preventable disease and people have the power to do something about it in a way they don’t with many other cancers,” she said.