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Colorectal Cancer Screening

Given the nation's high incidence rates and low colonoscopy acceptance, action is needed

Learning Objectives
The goal of this continuing education article is to inform nurse practitioners about colorectal cancer screening. After reading this article, the nurse will be able to:
1. Identify prevention and risk reduction strategies related to CRC.
2. State available options for CRC other than a colonoscopy and identify advantages and disadvantages of each of these options.
3. Describe current screening guidelines for CRC.

Colorectal cancer (CRC) is the third most common cause of death worldwide.1 CRC is one of the most preventable causes of cancer death, and this fact necessitates more aggressive early detection and mass screening programs.2

Despite the worrisome statistics, participation in CRC screening continues to be low. This is due in part to ongoing debates about which screening option is the best for patients who are at average risk (i.e., patients without a family history of CRC).2,3 Newer, noninvasive stool-based testing may offer an opportunity to increase screening rates for CRC. An increasing amount of evidence and research supports such newer types of testing.4

This continuing education article reviews current recommended guidelines for CRC screening with attention to screening choices that do not involve colonoscopy.

Guidelines for CRC Screening
In 2000, the American College of Gastroenterology (ACG) issued CRC screening recommendations that endorsed colonoscopy every 10 years starting at age 50 as the preferred approach.3 In 2008, the ACG issued changes to this guideline, dividing screening tests into two categories: cancer prevention and cancer detection. Prevention testing was designated the preferred option.3

Cancer prevention testing has the potential to image both cancer and polyps, while cancer detection testing typically has low sensitivity for polyps and even lower sensitivity for cancer compared to prevention testing.3 As of 2015, the ACG continues to recommend a preferred CRC prevention test (colonoscopy every 10 years) and a preferred CRC detection test (fecal immunochemical test, or FIT) annually to detect occult bleeding.3

Advantages of colonoscopy for CRC screening include:3

  • It is widely available.
  • It allows visualization of the entire colon.
  • Diagnosis and treatment can be determined in a single session.
  • It is the only test that is recommended at 10-year intervals.

Disadvantages of colonoscopy for CRC screening include:

  • Necessary bowel preparation. Up to 25% of patients will have an inadequate prep which may result in undiagnosed adenomas.9  
  • Sedation is typically required, forcing the patient to need a ride home and miss an entire day of work.9
  • 1 in 1,000 patients may experience serious bleeding or a tear in the intestinal wall.9

Other reasons that patients choose not to have a screening colonoscopy for CRC include a fear of invasive procedures and sedating medications, embarrassment about the procedure, fear of the procedure being painful, and past negative experiences with the procedure.9For patients who decline a colonoscopy or if this option is unavailable, an alternative CRC prevention test should be considered.3 These alternatives are flexible sigmoidoscopy every 5 to 10 years, computed tomography colonography every 5 years, or FIT every year.

Anyone who faces an average risk for CRC should be screened beginning at age 50 (men and women), with the exception of black patients, who should start screening at age 45.3 A family history of polyps should not prompt earlier screening unless there is evidence that the polyp was an advanced adenoma.3

The ACG guidelines identify heavy cigarette smoking and obesity as linked to an increased risk of CRC development at an earlier age.3 Smoking has been linked to 20% of all CRC cases in the United States, and it is one the of the strongest predictors of CRC in the Physicians' Health Study.3 Literature states that people who have more than 20 pack-years of smoking face 2 to 3 times the risk of developing CRC compared to nonsmokers.3 Smokers are also more likely to present with advanced stage CRC than nonsmokers.3

Obesity is also associated with colon adenomas. Obesity doubles a patient's risk of developing high-risk adenomas (>1 cm).3 Abdominal obesity is a stronger risk factor than truncal obesity.3

Given the increased CRC risks associated with smoking and obesity, the ACG recommends that CRC screening be initiated earlier, at age 45, in smokers with a 20 pack-year history and in obese patients.3 The ACG states that earlier screening for these populations has been proven both beneficial and cost-effective.3

Screening Options
CRC screening decisions should evaluate multiple options and include an assessment of patient preferences.5 Options other than a colonoscopy are available: FIT, fecal DNA, flexible sigmoidoscopy and CT colonography.5 Double-contrast barium enema is no longer recommended as a CRC screening option because its ability to detect polyps is lower than that for CT colonography.2 All options should be discussed and considered with patients, especially those who refuse a colonoscopy.

FIT testing was approved by the FDA in 2001. It directly detects human globin within hemoglobin.6 FIT does not require dietary restrictions, and a single sample is sufficient for testing.6 Sensitivity (25% to 72%) and specificity (59% to 97%) vary, and studies suggest that detection rates with the use of FIT are comparable, if not superior, to guaiac fecal occult blood testing.6

To collect a proper specimen for FIT testing, patients are usually sent home with a kit that includes a brush and testing cards. The patient is instructed to flush the toilet before having a bowel movement and use a collecting device such as rice paper or a plastic specimen container so that the stool does not make contact with the toilet water.9 A specimen should be collected by using the provided brush and placed on the testing card. At least two to three samples produced on different days should be collected and then sent to the laboratory.9 Obtaining a single specimen at time of digital rectal exam is not recommended because of extraordinarily low sensitivity, and all patients with positive results should be referred for further testing.6

Advantages of FIT testing include that it is easy to use, there are no drug or diet restrictions, and the test is less likely to react with bleeding from the upper digestive tract, such as the stomach.9 Disadvantages include that it might not detect a tumor or polyp that is not bleeding, requiring multiple stool samples to be tested.9 The test is completed at home, so there is a possibility for incorrect specimen collection by the patient. FIT testing may produce false-positive results and the test needs to be completed yearly.9 If the results are positive, a colonoscopy is required.9

Fecal DNA testing is a newer use for CRC screening that is on the rise. The test works by detecting the presence of DNA alterations during colorectal carcinogenesis in tumor cells sloughed into stool.6 In studies, fecal DNA testing was able to detect 52% of CRC cases with 94% specificity in a subgroup analysis compared to 13% by fecal occult blood testing, which had a specificity of 95%.6 There is no rationale for the primary use of fecal DNA testing as a CRC detection test.3

Cologuard is the first FDA-approved at-home fecal DNA test. The patient receives a kit in the mail, which contains a sample container, a bracket to hold the container in the toilet, liquid preservative, a tube, labels and a shipping box.9 A sample of stool is collected into the specimen container without getting urine mixed in. Liquid preservative is poured over the sample, and it is shipped back according to instructions in the kit.9 Results are mailed to the patient in a few weeks. Positive results require the patient to receive a colonoscopy. As with FIT testing, the possibility for a contaminated specimen is also a possibility with at home fecal DNA testing.

Disadvantages to fecal DNA testing include expense ($400 to $600). In 2014, the Centers for Medicare and Medicaid Services established a reimbursement rate of $502 per test.10 Medicare will cover the cost of this test once every 3 years.10 Most insurance plans cover the cost of Colorguard testing. However, due to variations in deductibles and co-pays, out-of-pocket costs vary and the patient should check with their insurance carrier for specific details prior to testing.

Other disadvantages include a lack of established data on which to determine an optimal interval, and lack of recommendations on how to respond to patients who have a positive fecal DNA test but a negative colonoscopy result.3 Although no established guidelines for fecal DNA testing intervals exist, the ACG states that testing at intervals less than 3 years would be cost prohibitive.3 Given some of its disadvantages, increasing evidence shows that fecal DNA testing may provide a valuable noninvasive option for patients who are unable or unwilling to have a colonoscopy.6

Since 2000, the use of flexible sigmoidoscopy for the detection of CRC has declined in the United States. However, it is still being used in certain settings.3 This test is similar to a colonoscopy, but less of the colon is visualized (only the distal colon and rectum). Bowel preparation is typically less effective, and patients are not sedated.1,3 A sigmoidscope of at least 60 cm in length should be used, and any patients with polyps larger than 1 cm should be referred for a colonoscopy because lesions this size are highly suspicious for being adenomas and are also associated with a risk for proximal colonic neoplasms.1,6

CT colonography (virtual colonoscopy) is an evolving screening option for CRC. Advantages include that it is minimally invasive, provides a structural exam of the entire colon with high sensitivity for detection of advanced neoplasia, takes around 10 minutes to complete, and no sedation or recovery time is needed.7 Patients can return to work the same day.7 A bowel preparation is required the day before, and testing includes placement of a rectal tube with bowel insufflation.7

Concerns about CT colonography for CRC screening are dominated by exposure to radiation. The reported dose of radiation is estimated at 10 mSv, and experts suggest that 1 in 1,000 patients would develop cancer in a lifetime after being exposed at the dose used for CT colonography.6 Technical aspects of testing, such as imaging, pre-procedure preparation and expertise of interpretation of results, have not been standardized.6 Testing should be repeated every 5 years, and patients with positive findings of a polyp larger than 5 mm should be referred for a colonoscopy.6 CT colonography also has limited reimbursement as a firstline screening tool. The more accepted indication is an incomplete colonoscopy.7

Risk Reduction
Risk factors that may increase a patients chance of having CRC include age, family history of CRC, inherited risk, alcohol use, cigarette smoking, and obesity.11 Increasing protective factors may decrease the chance and help prevent a patient from developing CRC. These protective factors include physical activity, use of aspirin, combination hormone replacement therapy, and polyp removal through colonoscopy.11 The use of aspirin daily for at least 5 years has been shown to decrease the risk of CRC and the risk of death from CRC.11 Combination hormone replacement therapy containing both estrogen and progestin lowers the risk of invasive CRC in postmenopausal woman, but it will not lower their risk of dying from CRC.11 Eating a diet low in animal fats and high in fruits, vegetables and whole grains may also reduce the risk of CRC.11

Emphasize the Importance of Screening
The key to preventing CRC is screening. CRC almost always develops from precancerous polyps growing in the colon. Screening tests can find these precancerous polyps so that they can be removed before they develop into CRC.11 Screening tests also aid in early detection of CRC, and that is when treatment works the best.11 Twenty-eight million Americans are not up-to-date on their screening for CRC, and 51,000 people die of CRC each year.11 Use of recommended screenings could prevent up to 60% of these deaths.11

Decisions about CRC screening options require an evaluation of multiple options and should include an assessment of patient preferences.5 CRC mortality can be reduced through early detection and diagnosis with the use of the testing options discussed in this article.

Colonoscopy remains the preferred method of screening by gastroenterologists. Colonoscopy is also required to confirm positive findings of other testing methods.6 Patients who decline colonoscopy should be offered one of the available alternative screening tests.

Use of noninvasive testing for CRC, such as fecal DNA and FIT, may increase screening for CRC by providing patients with more options other than invasive testing. Noninvasive tests require no bowel prep and can be done in the privacy of the patient's home increasing the chances for patient compliance with screening for CRC. Being familiar with current guidelines and screening options for CRC is important when assisting patients in making an informed decision about colorectal cancer prevention and diagnosis.

References
1. Bretthauer, M. Colorectal cancer screening. J Intern Med. 2011;270(2):87-98. doi:10.1111/j.1365-2796.2011.02399

2. Hewitson P, et al. Cochrane systematic review of colorectal cancer screening using the fecal occult blood test (hemoccult): An update. Am J Gastroenterol. 2008;103(6):1541-1549. doi:10.1111/j.1572-0241.2008.01875

3. Rex D, et al. American College of Gastroenterology guidelines for colorectal cancer screening 2008. Am J Gastroenterol, 2009;104(3):739-750.

4. Robertson DJ, Imperiale TF. Stool testing for colorectal cancer. Gastroenterology. 2015;149(5):1286-1293. doi 10.1053/j.gastro.2015.05.045

5. Imaeda A, et al. What is most important to patients when deciding about colorectal screening? J Gen Intern Med. 2010;25(7):688-693. doi:10.1007/s11606-010-1318-9

6. Burt R, et al. NCCN clinical practice guidelines in oncology. Colorectal cancer screening. J Natl Comprehensive Cancer Network. 2010;8(1):8-61.

7. McFarland E. Revised colorectal screening guidelines: Joint effort of the American Cancer Society, U.S. Multisociety Task Force on Colorectal Cancer, and American College Of Radiology. Radiology. 2008;248(3). http://dx.doi.org/10.1148/radiol.2483080842

8. Ling B, et al. Physicians encouraging colorectal screening: a randomized controlled trial of enhanced office and patient management on compliance with colorectal cancer screening. Arch Intern Med. 2009;169(1):47-55.

Sandra Barto is a family nurse practitioner at UPMC Passavant in Pittsburgh. She has completed a disclosure statement and reports no relationships related to this article.




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