Colorectal Cancer Screening:
Who Should Be Screened

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What is Colon Cancer? Cancer Screening

by David A. Garcia, MD

Having recently participated in a colorectal cancer screening lecture, I was impressed by the number of questions from the public as well as medical providers with regard to the risk factors for colorectal cancer and current recommendations for colorectal cancer screening.

Risk Factors

Average Risk Patient

• Age older than 50 years

• No personal history or family history of colon cancer

• No personal history or family history of colon polyps

Recommendations

Screening interval is indicated by findings on the initial screening test such as occult blood, abnormal DNA in stool, polyps, colorectal cancer, and family history.

Fecal Occult Blood Testing (FOBT): This test is inexpensive, convenient, and non-invasive in that it does not require special equipment other than an occult blood testing card. It can be performed at home and mailed to a laboratory. FOBT has a high sensitivity for heme (blood), but it has a low specificity for colon cancer. This test is recommended yearly. If occult blood is detected, the further gastrointestinal evaluation is recommended.

Flexible Sigmoidoscopy (FS): This test is invasive and is routinely preformed without sedation. FS surveys only the left colon. Historically, 29 percent of left-sided colon polyps smaller than one centimeter (cm) have been associated with right-sided colon lesions, while 75 percent of left-sided colon polyps greater than one cm have been associated with more advanced right-sided colon lesions. This exam is recommended every five years. Colonoscopy is recommended if polyps or lesions are found.

Air Contrast Barium Enema (ACBE): This test is invasive in that an enema is inserted into the rectum. The colon is then insufflated with air and barium is infused into the colon. ACBE is routinely performed without sedation. This exam does expose the patient to radiation. Although this radiation exposure is initially a small amount, it is likely to increase with repeated screenings. A cathartic is required to cleanse the colon of debris such as stool that can be misinterpreted as polyps or lesions. Unfortunately, as many as 50 percent of colonic polyps and lesions one cm or smaller can be missed. This exam is recommended every 10 years. Colonoscopy is recommended if polyps or lesions are detected.

CT Colonography (CTC): This test is invasive in that an enema is inserted into the rectum. The colon is then insufflated with air. CTC is routinely performed without sedation. This exam does expose the patient to radiation. Although, this radiation exposure is a small amount, it is likely to increase with repeated screenings. A cathartic is required to cleanse the colon of debris such as stool that can be misinterpreted as polyps or lesions. Unfortunately, polyps less than one cm may not be detected. CTC is recommended every 10 years. Colonoscopy is recommended if polyps or lesions are detected.

Fecal DNA Testing (FDT): This is a non-invasive test. FDT is more expensive that FOBT. FDT may be performed at home. This test detects up to 52 percent of colon cancers and 15 percent of large polyps. FDT is recommended every five years if negative. Colonoscopy is recommended if abnormal DNA is detected.

Capsule Colonoscopy: This exam is not currently available. It will be minimally invasive, although it will be expensive. Detected polyps cannot be removed. There is the possibility of intestinal obstruction by the capsule when strictures are encountered. Colonoscopy is recommended for abnormal exams. Colonoscopy: This exam is invasive. Sedation is routinely used. Time off from work is required due to sedation. Colonoscopy is operator dependant, as are the other exams mentioned above. In experienced hands, colonoscopy has a sensitivity and specificity of 95 percent to 98 percent. Colonoscopy surveys the entire colon and terminal ileum. A colon prep is required to cleanse the colon of any debris. Polyps can be removed and lesions can be biopsied. Colonoscopy is recommended every 10 years for average risk patients, and every three years for high risk patients. Colonoscopy is covered by Medicare and most insurance.

Patients at high risk for colorectal cancer include:

1) Family history of colorectal cancer or adenomatous colon polypsis in first degree relative younger than 50. Screening colonoscopy interval is every one to three years as indicated by findings on the initial colonoscopy such as polyps or colorectal cancer.

2) Personal history of colorectal cancer or adenomatous polypsis. Patients with adenomas larger than one cm, flat adenomas, or more than three ademonatous polyps should have screening colonoscopy every one to three years.

3) Familial Adenomatous Polyposis Syndrome (FAP). Patients with a first degree relative with FAP should have gene testing for APC (Adenomatous Polyposis Coli) gene at 10 years to 12 years old. Patients with the confirmed APC (Adenomatous Polyposis Coli) gene should begin yearly screening sigmoidoscopy at 12 years old. If polypsis is present at the initial screening examination, then colectomy should be considered due to inevitable colorectal cancer by 39 years old. If examinations are negative for polyposis, then the screening interval decreases with each subsequent decade. Patients are considered average risk at age 50 if polyposis is consistently absent.

4) Hereditary None Polyposis Colorectal Cancer (HNPCC). Patients with HNPCC have a 70 percent to 80 percent lifetime risk of developing colorectal cancer. Patients with HNPCC are characterized by having:

• Colorectal cancer involving at least two generations;

• One or more colorectal cancer cases diagnosed before age 50; and

• Extracolonic cancers including endometrium, upper GI tract, and urinary tract. Screening colonoscopy is offered every one to two years starting at age 20 to 25, or 10 years earlier than the youngest age of colorectal cancer in a primary relative.

5) Inflammatory Bowel Disease (Crohn’s Disease and Ulcerative Colitis). Screening colonoscopy is offered every one to two years with four quadrant biopsies every 10 cm to rule out dysplasia in patients with more than eight years of disease with pancolitis and more than 15 years of disease in left-sided colitis.

Conclusion

Screening for colorectal cancer is an invaluable tool, and its use is imperative since approximately 93 percent of cases of colorectal cancer are diagnosed over age 50, and approximately 80 percent of colorectal cancer patients have sporadic disease with no evidence of an inherited disorder. Thirty-nine percent of colorectal cancers found during a colonoscopy are at an advanced stage. Screening colonoscopy with clearance of polyps results in a 70 percent to 90 percent reduction of colorectal cancer.

David A. Garcia, MD is a gastroenterologist in solo practice in the Stone Oak area. Dr. Garcia is Chief of Internal Medicine at North Central Baptist Hospital. After completing training at Scott & White in Temple, Texas, Dr. Garcia received board certification in Gastroenterology and Internal Medicine.