Screening for colorectal cancer: need for controlled trials

Article Abstract:

It was estimated that more than 150,000 new cases of colorectal cancer and over 65,000 deaths from this disease will occur in 1990 in the United States. The chance that a person will develop cancer of the large intestine in his or her lifetime is five percent. Fortunately, colorectal cancer can be detected and treated at an early stage. The risk of developing this malignancy increases with age after 50 years, a family history of colorectal cancer, and persistent ulcer formation and inflammation of the colon. Two methods of screening for colorectal cancer include fecal occult blood testing, and flexible sigmoidoscopy, the examination of the colon using a fiberoptic device. Studies are underway to evaluate the effectiveness of these screening methods in decreasing the death rate due to colorectal cancer. Two methods for examining the entire colon include: colonoscopy, the internal examination of the colon using a tube-like instrument with an optical system; and barium enema, in which a radioactive substance is used to produce X-ray images of the colon. Colonoscopy can be used to obtain tissue samples and remove tumors, and is more effective than barium enema in detecting smaller malignant growths. The costs and risks of screening by any method must be assessed before the method can be used to screen the general population. Mathematical models have been developed to study the benefits and risks of screening for colorectal cancer. One model estimated that screening a person 50 to 75 years of age will decrease the chance of dying from this disease by 10 to 75 percent, depending on the type and frequency of the screening method. In addition, it was recommended that every three to five years, persons with an average risk should be screened using fecal occult blood tests and sigmoidoscopy, whereas those with a high risk should undergo a barium enema or colonoscopy. These screening recommendations were based on mathematical models and must be evaluated in human studies. (Consumer Summary produced by Reliance Medical Information, Inc.)

Methods, Barium enema, editorial, Sigmoidoscopy

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Hemoccult screening in detecting colorectal neoplasm: sensitivity, specificity, and predictive value

Article Abstract:

Colorectal cancer is the second most common cancer in the United States. The rate of death from colon cancer is 60 percent overall, but mortality can be reduced to 20 percent if the cancer is detected early. The American Cancer Society recommends: a physical examination of the rectum every year for persons over age 40 years; a fecal occult blood test or examination of feces for blood each year; and a sigmoidoscopy, the examination of the lower portion of the large intestine leading to the rectum, every three to five years for those over age 50 years. Studies suggest that fecal occult blood testing may be a sufficient method of screening for colorectal cancer. The sensitivity, specificity, and predictive value of the Hemoccult II test, a fecal occult blood test, for detecting colorectal neoplasm was evaluated. The sensitivity of Hemoccult II tests was 50 percent for colorectal cancer diagnosed within a year of testing, 43 percent within two years, and 25 percent within four years. For detection of polyps, tumors with pedicles or stem-like structures, sensitivity of the Hemoccult II was 36 percent at one year, 28 percent at two years, and 17 percent at four years. Specificity of the Hemoccult II test was 99 percent. Many of these patients had symptoms. The overall results indicate that if hemoccult II slides are the only technique used to screen for colorectal cancer without symptoms, 50 to 60 percent of cancers will go undetected. (Consumer Summary produced by Reliance Medical Information, Inc.)

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A comparison of fecal occult-blood tests for colorectal-cancer screening

Article Abstract:

The HemeSelect test for fecal blood, when used alone or in combination with the Hemoccult II Sensa test, is more sensitive than the Hemoccult II test in detecting colorectal cancer. These tests are designed to detect very small amounts of blood in stool samples, which may indicate colorectal tumors that have not caused symptoms. The three types of tests were mailed to 10,702 people at least 50 years old and 8,104 of these people returned at least one usable test. The accuracy of the test was based on sigmoidoscopy and colonoscopy results during the subsequent two years. The probability that people with carcinomas would be correctly identified was 79% with Hemoccult II Sensa, 69% with HemeSelect, 66% with a combination of these two, and 37% with Hemoccult II. The Hemoccult II and the combination Hemoccult II Sensa and HemeSelect most accurately identified people without carcinoma as they were least likely to produce false positive results.

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