Q&A on colon cancer testing

Mar. 27, 2008 (McClatchy-Tribune Regional News delivered by Newstex) --
Colon cancer is the No. 2 cancer killer of American men and women, so early detection and removal of polyps that can become cancerous is important.

This year, the American Cancer Society has updated its guideline recommendations for early detection of colon cancer, guidelines used by many medical professionals and patients. ACS said the overriding goal of this update is to provide a practical guideline for physicians and the public to make better informed decisions about colon cancer screening.

For the revised guidelines, ACS used a panel of experts who concluded that colon cancer prevention should be the primary goal of colorectal cancer screening.

The screening tests are designed to detect both early cancer and pre-malignant or adenomatous polyps and are encouraged for those willing to undergo invasive tests, such as flexible sigmoidoscopy, optical colonoscopy, air-contrast barium enema and CT colonography.

Understanding these tests, plus other tests that involve stool samples, can be complicated, so the American Cancer Society has created a Q&A to help people understand the new guidelines, tests and recommendations. The following is a shortened version of that Q&A:

1. What are the new recommended guidelines for early detection?

One of the following tests are acceptable options for the early detection of colorectal cancer and adenomatous polyps for adults 50 and older who are of average risk and have no symptoms:

--Flexible sigmoidoscopy (FSIG) every 5 years

--Colonoscopy (CSPY) every 10 years, or

--Double contrast barium enema (DCBE) every 5 years

--CT colonography (CTC) every five years

One of the following tests primarily detect cancer:

--Annual guaiac-based fecal occult blood test (gFOBT) with high test sensitivity for cancer

--Annual fecal immunochemical test (FIT) with high test sensitivity for cancer, or

--Stool DNA test (sDNA) with high sensitivity for cancer, interval uncertain

2. What is new and significant in these 2008 guidelines?

--Two new tests are now recommended as options for colorectal cancer screening. They are stool DNA (sDNA) and computerized tomographic (CT) colonography.

--For the first time, screening tests are grouped into categories based on performance characteristics: Those that primarily detect cancer early and those that can also detect precancerous polyps.

A. Tests that primarily detect cancer early are fecal (stool) tests, including guaiac-based and immunochemical-based fecal occult blood tests (gFOBT & FIT), and stool DNA tests (sDNA).

B. Tests that detect both precancerous polyps and cancer include flexible sigmoidoscopy, optical colonoscopy, double contrast barium enema, and computerized tomographic (CT) colonography.

3. What are the major changes to these guidelines compared with previous reviews?

--One significant change is the grouping of colorectal cancer screening methods into those that primarily identify cancer and those that both detect cancer and precancerous polyps, with a preference for those tests that can both detect cancer and prevent it by detecting pre-malignant polyps, which can then be removed.

--Another change is the panel's recommendation that options for screening must be able to detect the majority of cancers present at the time of testing. This criterion is based on expert opinion, and these considerations:

A. Recent evidence has revealed an unacceptably wide range of sensitivity among some gFOBT strategies, with some practices and tests performing so poorly that the large majority of cancers are missed at the time of screening.

B. A test such as gFOBT that demonstrates poor test sensitivity, but good program sensitivity depends on high rates of regular screening. But many patients have only one test and do not return for annual testing and recommended regular screening intervals.

Because of A. and B. the guidelines panel concludes that physicians and institutions should select only stool blood tests that have been shown in the scientific literature to detect the majority of prevalent colorectal cancers in an asymptomatic population. The panel also adds two new tests as acceptable options: CT colonography every 5 years, and sDNA testing, for which the optimal screening interval is currently unknown.

4. What two categories of colon cancer screening were reviewed?

--Tests that are more likely to detect both cancer and premalignant polyps

Tests in this category are structural exams, including flexible sigmoidoscopy (FSIG), optical colonoscopy (CSPY), double contrast barium enema (DCBE), and computerized tomographic (CT) colonography. The higher likelihood of polyp detection with the use of these tests substantially increases opportunities for removal of polyps and the associated prevention of colorectal cancer.

--Tests that are primarily effective at finding cancer early

Fecal (stool) tests include: guaiac-based and immunochemical-based fecal occult blood tests (gFOBT & FIT), and stool DNA test (sDNA). These tests primarily identify the existence of colorectal cancer. Some precancerous polyps may be detected by these tests, providing an opportunity to remove them and prevent colorectal cancer, but the opportunity for prevention is both limited and incidental and can not meet the primary goal of colorectal cancer screening.

5. What are the early detection guidelines for those at increased risk ?

The update guidelines focus on screening in average risk adults. Individuals at increased risk should continue to follow recommendations issued previously. That includes risks due to a history of adenomatous polyps, a personal history of curative-intent resection of colorectal cancer, or a family history of either colorectal cancer or colorectal adenomas diagnosed in a first-degree relative before age 60, or high-risk, due to a history of inflammatory bowel disease of significant duration, or the presence of one of two hereditary syndromes.

6. If structural tests such as colonoscopy can prevent cancer, why not recommend only these tests?

ACS says these tests require bowel preparation and an office or hospital visit, and they have various levels of risk to patients. They also have limitations, greater patient requirements for successful completion and potential harms. The panel also recognizes that some patients will not want to undergo an invasive test that requires bowel preparation, may prefer to have screening in the privacy of their home, or may not have access to the invasive tests due to lack of insurance or medical coverage or local resources.

7. What are the benefits and limitations of the fecal tests?

The primary advantage of these tests is that collection of fecal samples for blood or DNA testing can be performed at home, without bowel preparation. Fecal occult blood tests are also inexpensive on a per test basis when compared to other screening methods.

However, these tests are less likely to lead to cancer prevention compared with the invasive tests; they must be repeated at more frequent intervals to be effective; and if the test is positive, colonoscopy is required. It must also be recognized that some stool tests (particularly older versions of guiaic-based tests) do not detect the majority of cancers present at the time of testing, and should therefore not be used for colorectal cancer screening.

8. Why is sDNA now recommended, and what are its strengths and limitations?

sDNA testing is a relatively new method of colorectal cancer screening. Cancer cells that contain altered DNA are continuously shed into the large bowel and passed in the feces, and this altered DNA can be isolated and identified through this screening test.

In previous assessments, both the American Cancer Society and the U.S. Multi-Society Task Force concluded that data were insufficient to recommend screening with sDNA for average risk individuals. Based on the accumulation of evidence since the last update of these guidelines in 2003, there is sufficient data to conclude that sDNA testing meets the threshold criterion of detecting the majority of prevalent and incident cancers at the time of testing.

ACS notes that an obvious limitation of sDNA testing is that test sensitivity is based on a panel of markers that appears to identify most, but not all, colorectal cancers. Further, it is not known what proportion of advanced adenomas (pre-cancerous polyps) is identified with the current commercially available version of the stool DNA test. That's why patients need to be informed that the current test will detect some but not all cancers and some polyps.

9. Why is CT colonography (CTC) now recommended?

Recent data suggest CTC is comparable to optical colonoscopy for the detection of cancer and polyps of significant size when state-of-the-art techniques are applied. Provided that advanced, proven techniques are employed in the clinical setting, CTC is included in the guidelines as an option for colorectal cancer screening and prevention in average-risk adults age 50 years and older.

10. What are CT colonography's strengths and limitations?

CTC provides a time efficient procedure with minimal invasiveness. No sedation or recovery time is required, nor is a chaperone needed to provide transportation after the procedure. Time permitting, patients can return to work on the same day.

Several limitations of CTC exist. Since it is an "image-only" test, patients with polyps of significant size will require colonoscopy to remove the polyps. CTC also requires the same full bowel preparation and restricted diet as optical colonoscopy, which may decrease patient adherence. While same-day polyp removal can be offered without the need for additional preparation, this requires coordination between medical specialists (radiologists and endoscopists) and facilities (radiology departments and endoscopy suites).

Reimbursement for CTC is limited, although 47 states now offer Medicare reimbursement for diagnostic CTC for certain clinical indications (typically limited to patients who have had an incomplete optical colonoscopy).

Potential harms from CTC are related to the procedural risks associated with bowel preparation, colonic distention and radiation exposure due to CT scanning. The risks associated with bowel preparation are similar to those for optical colonoscopy. Because CTC is a minimally invasive test, the risk for colonic perforation due to distention is low.

11. Are the tests covered by insurance?

Costs of these different tests vary widely based not only on the type of test but also other fees (such as administration fees, office visit, etc.). With the exception of the newly added tests -- CTC and sDNA -- Medicare and most insurers already cover most or all colorectal cancer screening tests. Many major insurance plans may begin to cover the added tests (CTC and sDNA).

12. How will these revised guidelines help reduce deaths from colorectal cancer?

Screening of average risk individuals can reduce colorectal cancer mortality by detecting cancer at an early curable stage, and by detecting and removing advanced neoplasia. No screening test is perfect, either for cancer detection or polyp detection. Each test has advantages, limitations and risks. Patient preferences and availability of resources play an important role in the selection of screening tests.

This update of the guidelines place an emphasis on the value of preventing colorectal cancer, sought to address the importance of test sensitivity in the presence of low rates of programmatic screening and attempted to provide improved guidance about test characteristics to referring clinicians.

14. What is the history behind these guidelines?

Beginning in 1980, the ACS first issued formal guidelines for colorectal cancer screening in average risk adults. Since then, the society has periodically updated its colorectal cancer guidelines, and other organizations also have issued recommendations for colorectal cancer screening, most notably the U.S. Preventive Services Task Force and the U.S. Multi-Society Task Force on Colorectal Cancer (USMSTF; comprised of the American College of Gastroenterology, the American Gastroenterological Association and the American Society for Gastrointestinal Endoscopy).

Since 1997, the organizational guidelines for average risk adults have grown increasingly similar, and now largely represent a broad consensus on the value, options and methods for periodic screening for colorectal cancer.

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