Although colon cancer screening is recommended by many organisations, less clear is which method is best to detect tumors and precancerous lesions.

A new study in the New England Journal of Medicine suggests that a relatively inexpensive and non-invasive test may be just as effective as a colonoscopy.

Meanwhile, a 23-year study, also published in the journal, has confirmed that removing precancerous polyps, known as adenomas, during a colonoscopy can reduce the risk of death from colorectal cancer by half.

Based on the results, "an appealing concept would be to use colonoscopy as a triage screening test, offering it once for everybody at 60 years of age" and using it to classify people into high- and low-risk categories, Dr Michael Bretthauer of Oslo University Hospital and Dr Mette Kalager of Telemark Hospital, both in Norway, wrote in an editorial in the journal.

Low-risk people would not need further screening while those with adenomas would be evaluated regularly.

One in 20 Americans will develop colorectal cancer. About 140,000 cases are diagnosed in the US each year, resulting in about 49,000 deaths, according to the National Cancer Institute. It is the third most common cancer worldwide.

The US Preventive Services Task Force, a government-backed agency, recommends screening for people aged 50 to 75 years by one of three methods: a colonoscopy every 10 years; annual stool testing; or a less-thorough look into the colon (known as flexible sigmoidoscopy) every five years in conjunction with stool testing every two to three years.

People often find the tests unpleasant. For example, in the new study that compared stool testing with colonoscopy, only 34 per cent went along with stool testing. The participation rate was even lower when colonoscopy was offered, even though doctors can use it to cut away those suspicious precancerous adenomas.

In theory, adenoma removal saves lives by preventing a tumor. Ann Zauber of the Memorial Sloan-Kettering Cancer Center in New York, chief author of the long-term evaluation of polyp removal, and her colleagues said their work demonstrates that.

"This study is showing both a reduction in colon cancer incidence and colon cancer deaths by removing the adenomas, and it's a long-term effect" she said in a telephone interview. "This is reassuring for people to come in for screening."

The conclusion is based on people who were sent for a colonoscopy between 1980 and 1990. The Zauber team compared their death rate to the estimated death rate from the Surveillance Epidemiology and End Results (SEER) programme.

Over a period as long as 23 years, the rate from colorectal cancer among the 2,602 people who originally had adenomas removed was 53 per cent lower than estimated from the Seer data. In all, 12 died from cancer in the removal group, while 25 had normally been expected to die of colorectal disease.

The lower rate includes the fact that 81 per cent of the patients who had polyps removed continued to have periodic colonoscopies to check for growths.

Bretthauer and Kalager cautioned in their editorial that "the study mimics a situation in which 100 per cent of the population complies with screening, which is not a real-life scenario."

The ColonPrev study, being conducted in Spain, is designed to compare 10-year death rates in two groups: volunteers who received a one-time colonoscopy and volunteers who are being screened every two years using fecal immunochemical testing (FIT), a form of blood stool testing. A positive FIT test led to a colonoscopy.

After the first round of testing, the researchers report in the New England Journal of Medicine, colorectal cancer was found in 30 people in the 26,703-member colonoscopy group and 33 in the 26,599-person FIT group.

Colonoscopy uncovered twice as many advanced adenomas, about two percent of the sample versus one percent.

But the chief author of the Spanish study, Enrique Quintero of Hospital Universitario de Canarias, told Reuters Health that it was encouraging that the cheaper fecal test "detected half the advanced adenomas just in the first round."

The next round of FIT tests will uncover more growths, he predicted.

Death rates will not be examined until the 10-year follow-up is completed in 2021.

Quintero and his team also found that the people assigned to the FIT group were more likely to participate in screening than those who were in line for a colonoscopy.

The participation rates were 34 per cent with the stool-sampling test compared to 25 percent for colonoscopy.

At this point in the study, the researchers concluded, "the numbers of subjects who needed to be screened to find one colorectal cancer were 191 in the colonoscopy group and 281 in the FIT group, and the numbers who needed to be screened to find any advanced (cancer) were 10 and 36."

That's important when the FIT test is so much cheaper than a colonoscopy, Quintero said. "This simple, non-invasive and cheap test is equally good at detecting colorectal cancer and identifying the high-risk individual that should undergo a colonoscopy."

And the complication rate, including bleeding, low blood pressure and slow heartbeat, was nearly five times higher in the colonoscopy group. - Reuters