Though many people at risk for colorectal cancer never get screened for the disease, a new study has found that the vast majority of participants in a national trial were willing to undergo the examination known as flexible sigmoidoscopy.

More than eight of 10 study participants who were offered flexible sigmoidoscopy agreed to it, "reflecting the extent to which screening can be implemented in a motivated population," concluded a report published today in the Journal of the National Cancer Institute.

The study of almost 155,000 men and women is the largest to date on the early detection of colorectal cancer, which is second only to lung cancer as the nation's leading cause of cancer-related death.

Led by Dr. Joel Weissfeld, associate professor of epidemiology at the University of Pittsburgh Graduate School of Public Health, the study is part of the Prostate, Lung, Colorectal and Ovarian Cancer Screening Trial, a large-scale effort to determine whether certain screening tests reduce deaths from those cancers.

Yet many doctors prefer not to perform flexible sigmoidoscopies and would rather send their patients to have more extensive exams, called colonoscopies.

Unlike sigmoidoscopies, which examine the inside of the rectum and lower colon, colonoscopies examine the inside of the entire large intestine. They are administered by physician specialists and require patient sedation. They also are relatively expensive and involve more risk.

Sigmoidoscopies can be performed by family doctors or non-physicians and do not require sedation, but they can miss cancers because the entire colon is not examined.

"Doctors appear to be doing this test less," said Dr. Robert Smith, director of cancer screening for the American Cancer Society. Some doctors, he added, "don't feel it's a good use of their time for the amount of money reimbursed."

More and more people are getting colonoscopies for cancer screening, said Dr. Paul Lebovitz, chief of gastroenterology at Allegheny General Hospital.

But other screening tests for colorectal cancer are effective, he said, and increased screening would be beneficial.

Colorectal cancer screening lags far behind screening for breast cancer and cervical cancer, according to the Centers for Disease Control and Prevention.

Screening tests can find colorectal cancer in its earliest stages, when it can be treated more successfully, and also can identify precancerous polyps so they can be removed before they turn into cancer. More than 90 percent of colorectal cancers occur in people 50 and older.

The findings reported today involved men and women ages 55 to 74 who enrolled in the study from November 1993 to July 2001 and had no history of prostate, lung, colorectal or ovarian cancer. Participants drawn from the Pittsburgh area and nine other cities were randomly assigned to either a control group that was not offered flexible sigmoidoscopy or to another group that was offered the test.

The study found that women were more likely than men to decline the screening test and that refusal among women increased with age. The authors suggested that for those women, colonoscopy may be a better screening option.

Among those who underwent flexible sigmoidoscopy during the study, 23.4 percent had at least one polyp or mass that warranted further testing.

Of these, 74.2 percent had a follow-up sigmoidoscopy or a colonoscopy. The rate of cancer detected from the initial screening was 2.9 of 1,000 people screened.