The results from the first large randomized trial of sigmoidoscopy show that it is a more effective tool than mammography for breast cancer or PSA tests for prostate cancer, and confirm current U.S. guidelines suggesting regular sigmoidoscopy or colonoscopy to screen for colorectal cancer.
bowel, said Dr. Eric Esrailian, a gastroenterologist at UCLA's Reagan Medical Center.
"We don't often use the word ‘breakthrough,' but this is one of those rare occasions when I am going to use that word," Harpal Kumar, chief executive of Cancer Research UK, said in a news conference. "It is extremely rare to see the results of a clinical trial which are quite as compelling as this one."
The test not only identifies tumors in their early stage of development, when cure rates are about 90%, but also identifies and allows removal of polyps that may later grow into tumors. "That's a really good double benefit," Kumar said. Currently, only about 13% of all tumors are detected at that stage. And when symptoms develop, the cure rate is less than 50%.
Colorectal cancer is the third leading cause of cancer in the U.S., diagnosed in about 147,000 people every year and killing almost 50,000. But only about half the eligible U.S. population takes advantage of screening tests for it, according to the American Cancer Society.
"There has never been clinical trial evidence that removing polyps prevents cancer," said Dr. Wendy Atkin of Imperial College London, lead author of the new study, which was reported online in the journal Lancet. "There's been lots of indirect evidence, but this will be the first direct evidence."
Beginning in 1994, Atkin and her colleagues enrolled about 170,000 men and women at 14 centers in Britain. About two-thirds were assigned to the control group and the rest to undergo sigmoidoscopy. An estimated 71% of those assigned to the intervention actually underwent the procedure, in which a flexible tube with a small camera is inserted through the rectum to examine the lower third of the bowel, where more than half of all bowel cancers occur.
Polyps — fleshy protuberances that are often precursors of tumors — were snipped out with a special tool inserted through the tube.
After 11 years of follow-up, the incidence of colorectal cancer in those who actually underwent the procedure was reduced by 31% and deaths by 43%. So far, Atkin said, "there is no sign that the effect of the test is wearing off." She expects the decline in deaths to continue to grow as they monitor the participants for longer periods.
That is because most people have virtually all the polyps they are ever going to have by the time they are in their mid-50s, she said. "The test just takes a few minutes, and the benefit may last a lifetime."
At least three other large studies of screening by sigmoidoscopy are in progress in the United States, Norway and Italy. Results from the U.S. study, which gives repeat sigmoidoscopies every three years, are expected in the next year or two.
"The question remains whether performing the test more frequently might lead to more impressive decreases in mortality," said Dr. Durado Brooks, director of prostate and colorectal cancer for the American Cancer Society.
U.S. recommendations call for a colonoscopy — in which the entire length of the large intestine is examined — every 10 years after the age of 50 if it reveals no abnormalities or a sigmoidoscopy every five years. Virtual colonoscopies performed by CT scans and fecal blood tests are less effective.
Sigmoidoscopy has fallen into some disfavor, however, because reimbursement often does not cover a physician's costs, Brooks said. There is also a perception that colonoscopy is better, "which is not necessarily supported by the evidence," he added.
In many ways, a sigmoidoscopy is more convenient than a colonoscopy, Esrailian said. The patient takes only an enema on the morning of the test, not the unpleasant bowel-cleaning products. The patient also does not need to be sedated, which is generally done for colonoscopies, and the procedure can be done in the office by a nurse practitioner or physician's assistant.
However, "the main message is that there is a benefit to screening," he said. "It can potentially be lifesaving."