Genetic Testing
Colorectal Cancer Screening
Screening tests for colorectal cancer help diagnose cancer as early as possible and improve patient outcomes. Five types of tests are used to screen for colorectal cancer1:
- Fecal occult blood test (FOBT) is used to check the stool for blood only visible by a microscope. If the result is positive, this may be a sign of polyps, cancer, or other conditions.
- Sigmoidoscopy is a procedure to view inside the lower colon and rectum for polyps, irregular regions, or cancer. The procedure uses a thin scope, which can be inserted through the rectum into the sigmoid colon. The sigmoidoscope contains a light and lens to help navigate through the area and detect polyps or obtain tissue samples. These tissue samples are later viewed using a microscope to look for potential signs of cancer.
- Colonoscopy is a similar procedure but involves looking inside the entire colon and rectum. This procedure also involves a thin colonoscope, which is inserted through the rectum into the colon. Any abnormal findings are checked under a microscope.
- Virtual colonoscopy is a procedure that uses diagnostic imaging more specifically computed tomography (CT) to take a series of pictures of the colon. After the pictures are taken, a computer works to combine the pictures and generate a detailed image that may reveal polyps or other abnormalities on the inside of the colon.
- DNA stool test examines cell DNA in stool and looks for any genetic abnormalities that may suggest colorectal cancer.
- A digital rectal exam is usually conducted as part of an annual physical exam. A physician will insert a lubricated gloved finger to feel for anything unusual. However, past studies have shown digital rectal exams do not prevent colorectal cancer and therefore do not work as a screening method.
Risks of Colorectal Cancer Screening
- Colonoscopy risks include tearing the lining of the colon and bleeding which can be treated at a hospital. A colonoscopy also requires sedation and problems with sedation may arise such as difficulty breathing, irregular heartbeat, and heart attack.
- Sigmoidoscopy risks also include tearing and bleeding but this is less likely than during a colonoscopy. Also, sedation is not required for a sigmoidoscopy so heart and respiratory problems are unlikely to occur.
- A virtual colonoscopy has a decreased risk compared to both a sigmoidoscopy and colonoscopy. However, it is currently unknown whether the radiation from the x-rays during the CT exam is harmful.
- As will all testing, false-positives and false-negatives from DNA stool tests and FOBT can occur and facilitate unnecessary treatment or deter appropriate treatment.
Works Cited
1PDQ Screening and Prevention Editorial Board. (2019, March 15th). PDQ Colorectal Cancer Screening. Retrieved from National Cancer Institute: https://www.cancer.gov/types/colorectal/patient/colorectal-prevention-pdq
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