There's new evidence that regular screening for colon cancer has long-term benefits.
Testing for blood in the stool reduced the risk of death from colorectal cancer by as much as 32 percent and it seemed to keep the death rate low even after testing stopped, according to one study.
A second found that getting a regular colonoscopy, where a tube is put in the colon to look for and - in some cases - remove abnormal growths, was linked to a 68 percent reduction in risk. It also confirmed that, if no growths are found, people can safely wait 10 years for their next test.
But the findings do not compare the relative merits of the two methods, even though that may be tempting, wrote Drs. Theodore Levin and Douglas Corley in an editorial in the New England Journal of Medicine, where the studies appear.
"Both colonoscopy and fecal occult-blood testing are effective for colorectal cancer screening, and these new studies support current screening guidelines," said the duo, who are based at Kaiser Permanente Medical Centers in California - Levin in Walnut Creek and Antioch and Corley in San Francisco.
"Both tests have been improved since they were used among the participants in either study. However, the two studies are different, which makes direct comparisons of effectiveness difficult."
"These studies don't break new ground, but they put us on more solid footing in recommending colorectal cancer screening by the current methods and, in general, at the current intervals," said Dr. Greg Enders, a gastroenterologist at Fox Chase Cancer Center in Philadelphia, who was not connected with either study.
Colorectal cancer kills over 600,000 people worldwide each year, according to the World Health Organization. The American Cancer Society estimates that the U.S. has about 50,800 deaths per year, with 142,800 new cases annually, a rate that has been declining thanks to screening.
But doctors are still trying to discern how best to screen and how often.
The government-backed U.S. Preventive Services Task Force recommends people between ages 50 and 75 get screened by colonoscopy every 10 years, with a high-sensitivity fecal occult blood test every year or with a sigmoidoscopy every five years in addition to fecal occult blood testing every three years.
The test that looks for blood in the feces has been the safest, cheapest and least complicated. But unless a tumor is releasing blood, the test can miss it. If blood is found, a colonoscopy is done to look for cancer or remove suspicious growths.
For its evaluation of the blood test, a team led by Dr. Aasma Shaukat of the University of Minnesota in Minneapolis looked at records from 46,551 participants in the Minnesota Colon Cancer Control Study who were followed for 30 years.
People were either screened for fecal blood annually, every two years or not at all. However, the formal screening program only spanned two six-year windows. The researchers had no follow-up information on which patients received subsequent screening with the blood test or a colonoscopy.
Nonetheless, the people who received annual screening during those initial periods ultimately saw a 32 percent reduction in their risk of dying from colorectal cancer. With biennial screening, the risk was cut by 22 percent. Screening did not affect the overall risk of dying during that period.
In total, 732 of 33,020 deaths over the 30 years were from colorectal cancer.
"You would expect to see a decrease in the risk of dying of colon cancer in the first eight to 10 years. The fact that the effect was sustained through 30 years is actually fairly remarkable," said Shaukat.
"It shows that the effect of colon cancer screening is profound," she said.
"The study of fecal occult blood testing provides the longest follow-up of any colorectal cancer screening study to date - an impressive 30 years - and shows that the benefits of screening by this method endure for the lifetime of the patient," Enders told Reuters Health in an email.
The researchers also found that with the fecal blood test, the greatest benefit was among men age 60 to 69. Their risk of death from colon cancer dropped by 54 percent compared to men of that age who were not screened.
The study on colonoscopies also looked at a less-thorough technique, known as a sigmoidoscopy, where a tube is only inserted into the end of the large intestine. A colonoscopy examines the full length. The information on 88,902 people, followed over 22 years, came from two databases: the Nurses' Health Study and the Health Professionals Follow-up Study.
Screening with sigmoidoscopy was tied to a 41 percent reduced risk of death from colorectal cancer. A full exploration of the colon by a colonoscopy was linked to a 68 percent lower risk.
The study "lays to rest a lingering concern that colonoscopy might not be more effective than sigmoidoscopy in preventing colorectal cancer deaths," said Enders. "National medical societies and Medicare have gone ‘all in' on the common sense notion that more endoscopy - that is colonoscopy - is better, but convincing data were not in hand."
Having a colonoscopy every three years or less - even though no suspicious growths were seen - was tied to a 65 percent reduced risk of colorectal cancer. The reduction was 60 percent if done every three to five years and 48 percent if done every five to 10 years.
Co-author Dr. Shuji Ogino of the Dana-Farber Cancer Institute in Boston said the findings suggest that when no growths are found, a colonoscopy doesn't need to be repeated for a decade.
Up to now, "there has not been good solid evidence to support a 10-year interval," he told Reuters Health. "But now we know that with low risk individuals, 10 years won't make a difference."
People with polyps or a family history of colorectal cancer will need more frequent examinations, he said.