An 18-year study of more than 46,000 people has found that a simple but little-used screening test might help prevent people from getting colon cancer.
The test, known as fecal occult blood screening, looks for traces of blood in the stool, a possible sign of a cancer or benign polyps that can be precursors to cancer. When these polyps are removed, cancer is prevented.
In the study, the colon cancer rate was reduced by as much as 20 percent among people who had the test.
The federally financed study, described in today's New England Journal of Medicine, was conducted by Dr. Jack S. Mandel, a vice president of Exponent, a Menlo Park, Calif., research company, and his colleagues, most of whom are at the University of Minnesota.
Dr. Ernest Hawk, chief of the gastrointestinal cancer group at the National Cancer Institute's division of cancer prevention, said that it was already known the test reduced the colon cancer death rate by allowing cancers to be detected early. But this was the first evidence that those who use the test can avoid colon cancer in the first place.
Hawk said that people whose colon cancer was detected in its earliest stage had a five-year survival rate of 90 percent, while those whose cancer is discovered in the latest stage, stage D, had just an 8 percent survival rate.
Colon cancer kills 65,000 Americans a year, making it the second-leading cause of cancer deaths for men and women, after lung cancer.
Besides the fecal blood test, doctors detect it by performing colonoscopies, in which a flexible scope is used to examine the entire colon, and sigmoidoscopies, in which a scope is used to examine the lower part of the colon, where most cancers occur. In addition, some doctors look for cancers with barium enemas.
But these tests are uncomfortable as well as being more expensive and elaborate than the fecal test. The fecal test is also the only one that has been shown in rigorous studies to reduce the colon cancer death rate, though doctors are convinced that the other tests have the same effect.
Few Americans have any colon cancer screening. The American Cancer Society estimates that only about a third of Americans older than 50 have ever been tested, and Mandel said it is estimated that at most a quarter of Americans older than 50 ever had a fecal occult blood test. He said that one reason for the dismal screening record is that doctors have tended not to recommend the test.
The fecal test, in particular, was mired in controversy because it was marketed for about 30 years before there was compelling evidence that it reduced the colon cancer death rate, he said.
Colon cancers begin as harmless polyps that can be found and removed. Some researchers had long hoped that screening tests could prevent the disease. If so, they said, the testing would offer an unprecedented opportunity to attack a devastating and common cancer.
In the new study, there were 417 cases of the cancer among 15,532 people who were offered annual fecal blood tests; 435 cancer cases among 15,550 people offered the test every other year; and 507 cases among the 15,363 people who did not have the test - about a 20 percent reduction in the cancer rate among those who were offered the screening test.
"What we had until now is evidence that early detection reduces the mortality from colon cancer," said Dr. Steven Woolf, a professor of family medicine at Virginia Commonwealth University who wrote an editorial accompanying the new study. "But early detection presumes the cancer already exists. This takes us to a new level."
The study began in 1975, nearly a decade after the fecal occult blood test was invented but before anyone knew whether it was effective in screening for colon cancer.
Their first result was published in 1993, showing that people who had the fecal blood test had a 33 percent reduction in their death rate from colon cancer. Two large European studies subsequently confirmed that result, Mandel said.
At the time, Mandel said, he predicted that the study might eventually show that the test helped to prevent cancer. But it took years of waiting for the prevention result to become apparent in these healthy people.
Mandel said he assumed that the people who were offered the screening test ended up having many more polyps removed than the control group - that, he said, was the only plausible explanation for the results. But since the control group was basically left alone, he did not know how many polyps were removed from these people.
While only fecal occult blood tests have been shown to prevent colon cancer, the logic behind the other screening tests indicates that they should have a similar effect, but it has not yet been proven in rigorous tests, Woolf said.