To view this article in PDF form, click here.

COLON CANCER
An update on screening

WHO SHOULD READ THIS?

Any PA who provides care for people older than 50 years or for those younger than 50 who are at increased risk for colorectal cancer (CRC) because they have one of the factors listed in “Who should be screened?”

WHY IS THIS IMPORTANT?

CRC is the third most common type of neoplasm and the second leading cause of cancer death in the United States for both men and women. The American Cancer Society (ACS) estimates that there were 153,000 new cases of CRC and 52,000 deaths attributed to the condition in 2007.¹ Early diagnosis and prompt intervention can reduce a person’s risk of developing CRC by up to 90%. CRC screening remains underused, despite the availability of effective screening tests. Today, fewer than 50% of adults are up to date with screening.²

WHO SHOULD BE SCREENED?

According to the National Cancer Institute (NCI) and other medical authorities, the exact causes of CRC are unknown, but several factors have been linked to increased risk of CRC. The addition of each factor listed below increases the overall risk.

Age older than 50 years
Personal history of CRC, colorectal polyps, or inflammatory bowel disease (ulcerative colitis and Crohn’s disease)
Family history of CRC, especially in any first-degree relative in whom CRC was diagnosed before age 60 years or in two or more first-degree relatives at any age¹
Race: African-Americans are at increased risk for upper CRC^3,4
Familial adenomatous polyposis and hereditary nonpolyposis colon cancer (Lynch Syndrome)
Sedentary lifestyle and a diet high in fat and calories and low in fiber (may increase risk).^3,5,6

WHAT ARE CURRENT SCREENING METHODS?

As outlined by the NCI, the type of CRC screening test used is based on several factors:⁴

Age, medical history, family history, and general health
Accuracy of the test
Risks associated with the test
Preparation required before the test
Sedation necessary during the test
Follow-up care after the test
Convenience of the test
Cost of the test and insurance coverage.

Both the ACS and the United States Preventive Services Task Force recommend periodic screening, but neither organization identifies a specific test as the gold standard (see Table 1).

Fecal occult blood test (FOBT) Sample is placed on specially prepared cards to test for the presence of blood. Advantages: No preparation needed; low cost; studies have demonstrated a reduction in relative mortality by 15% to 33% using this test.⁴ Disadvantages: Fails to detect most polyps and some cancers; false-positive results may be as high as 80%; dietary restrictions prior to testing may make compliance and follow-up poor; additional testing is required if results are positive for blood. Recommendations: Yearly testing.

Fecal immunochemical test Performed similarly to the FOBT. Advantages: More sensitive and specific than the FOBT; reduces the number of false-positive results; diet does not affect results.^1,5 Disadvantages: A positive result requires colonoscopy; multiple samples needed.⁴ Recommendations: Yearly testing.

Sigmoidoscopy Examines rectum and lower third of colon using a flexible scope. Advantages: Usually quick with few complications, minimal discomfort; less extensive preparation required compared to colonoscopy; may find up to 65% of polyps. Disadvantages: Misses upper two-thirds of the colon; has a very small risk of bleeding and tears to the lining of the colon; may require further workup depending on findings. Recommendations: Every 5 years, although no definitive data support more or less frequent examinations at this time. Studies are in progress. Performing both FOBT and sigmoidoscopy annually does not improve diagnostic yield compared to sigmoidoscopy alone.

Colonoscopy Examines the rectum and the entire colon and allows for biopsies and polyp removal. Advantages: Views the entire colon and rectum; both diagnostic and therapeutic; most sensitive test currently available. Disadvantages: May not identify all polyps and cancers; thorough preparation of the colon is necessary; sedation usually needed; although uncommon, bleeding and tears may occur; detection rates vary depending on endoscopist’s skill and rate of withdrawal from the colon. Recommendations: Every 10 years unless polyps seen on prior examination and then may be as often as every three years. Prospective research is currently under way investigating the precise frequency needed for this test.^1,5

Double contrast barium enema A series of x-rays following a barium enema and introduction of air into the colon. Advantages: Views the entire colon and rectum; rare complications; no sedation needed. Disadvantages: May not detect all polyps or cancers; thorough preparation of the bowel is needed; false-positive results are possible; may require further workup if findings are noted; has not been established as a reliable tool to screen for CRC. Recommendations: Every 5 years, but FOBT, sigmoidoscopy, or colonoscopy are preferred.

WHAT’S NEW IN CRC SCREENING?

Virtual colonoscopy (CT colonography) Performed in a spiral CT with contrast and air induced into the colon. Advantages: Less invasive; does not require sedation; performed quickly; possibly less costly than colonoscopy. Disadvantages: Bowel preparation required; diagnostic but not therapeutic; dependent on the ability of the radiologist and CT quality; does not catch small or flat polyps. Recommendations: Clinical trials underway to compare advantages and disadvantages with current methods. No recommendations for screening use at this time.

Fecal DNA testing Stool sample that looks for genetic alterations that occur in CRC cells that are subsequently shed into the stool. Advantages: Stool sample only; no preparation needed. Disadvantages: Experimental only. Recommendations: Under investigation. Early findings demonstrate higher sensitivity than FOBT with similar false-positive rates. More research is needed before recommendations or limitations of these studies will be made. Potentially, if valid, test would be performed every 5 years.

WHAT ELSE IS IMPORTANT TO KNOW?

Experts recommend that African-Americans begin screening at age 45 years because of the lower survival rates and delays in making the diagnosis of CRC in this population. Colonoscopy is the preferred screening test because of the propensity for lesions in the upper (proximal) colon in this group.

There is currently no recommended age to discontinue CRC screening. Rather, discontinuation is based on patient risk factors, life expectancy, comorbidities, and functional status.⁷ The clinician and patient make the decision for further screening.

The CDC has developed a CRC screening demonstrations program that can be accessed on the Web.⁸ This program is aimed at increasing CRC screening among low-income adults. PAs should view the site to determine if their patients are eligible. In addition, many free fact sheets are available for PAs and their patients, as well as other resources on cancer screening and assistance.

WHAT ABOUT GENETIC TESTING?

Inherited forms of colon cancer are rare, accounting for roughly 5% of all cases of CRC. Genetic syndromes that are of concern for CRC development include familial adenomatous polyposis, Lynch syndrome (hereditary nonpolyposis colon cancer), Pentz-Jeglers syndrome, and juvenile polyposis.

Some colon cancers appear to cluster in families, but to date a genetic link has not been identified. Researchers are currently working on identifying these family clusters and possible genetic links.² Genetic screening may be recommended for patients with a relevant family history, and earlier and more frequent screening will be performed. JAAPA

REFERENCES

	1.	Detailed guide: colon and rectum cancer. Can colorectal polyps and cancer be found early? American Cancer Society Web Site. http://www.cancer.org/docroot/CRI/content/CRI_2_4_3X_Can_colon_and_rectum_cancer_be_found_early.asp. Accessed February 5, 2008.
	2.	Preventive care: a national profile on use, disparities, and health benefits. Partnership for Prevention Web site. http://www.prevent.org/content/view/129/72/. Accessed February 5, 2008.
	3.	Colon cancer. MayoClinic.com. http://www.mayoclinic.com/health/colon-cancer/CO99999. Accessed February 5, 2008.
	4.	Agency for Health Research and Quality. Colorectal Cancer Screening. Summary, Evidence Report: Number 1. AHCPR Publication No. 97-0302. Rockville, MD: Agency for Health Care Policy and Research. http://www.ahrq.gov/clinic/colorsum.htm. Accessed February 5, 2008.
	5.	Colon and rectal cancer: screening and testing. National Cancer Institute Web site. http://www.cancer.gov/cancertopics/screening/colon-and-rectal. Accessed February 5, 2008.
	6.	Rex DK, Liangpunsakul S. Colorectal cancer screening. The American College of Gastroenterology. http://www.gi.org/patients/gihealth/pdf/colon.pdf. Accessed February 5, 2008.
	7.	Losey R, Messinger-Rapport B. At what age should we discontinue colon cancer screening in the elderly? Cleve Clin J Med. 2007;74(4):269-272.
	8.	Colorectal (colon) Cancer. Center for Disease Control and Prevention Web site. http://www.cdc.gov/cancer/colorectal/. Accessed February 5, 2008.

This article was written by Anthony E. Brenneman, MPAS, PA-C. Contributors included the other members and staff of CSAC: Lawrence M. Herman, MPA, PA-C, Chair; Alison C. Essary, MHPE, PA-C; Edward C. Hendrikson, PhD, PA-C; Marie-Michèle Léger, MPH, PA-C; Robert McNellis, MPH, PA; Daniel L. O’Donoghue, PhD, PA-C; and Eileen M. Van Dyke, MPS, PA-C. The manuscript was edited by Sarah Zarbock, PA-C.

COLON CANCER An update on screening