Colon Cancer Screening After a Family History and a Prior Adenoma
46-year-old woman with no symptoms requests “the best colon cancer test.” Her father had colon cancer at 52; a paternal uncle was diagnosed at 60. She had a colonoscopy at age 40 because of family history; one 6-mm tubular adenoma was removed, and the endoscopist advised repeat in 5–10 years. She has no known genetic mutation, no personal history of inflammatory bowel disease, and no symptoms. She is worried about missing cancer and asks whether a stool DNA test now would be sufficient. She is otherwise healthy, takes no medications, and has no family history of endometrial or ovarian cancer. Her father is alive at 72 after surgery. She has not discussed genetic testing with anyone. She is a nonsmoker and exercises regularly.
1. How should her family history and prior polyp affect the choice and timing of her next screening test?
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Her father’s diagnosis at 52 is a first-degree relative before age 60, so she is at increased risk and should have started screening at 40 or 10 years before the youngest diagnosis, whichever came first. She did. The 6-mm tubular adenoma is a low-risk adenoma; guideline-based surveillance is usually 7–10 years, but a strong family history often shortens that to about 5 years. Since her colonoscopy was 6 years ago, she is due now if a 5-year interval is chosen, and still within 7–10 years if not. Because she has both a personal adenoma and a family history, colonoscopy is preferred over a stool DNA test. I would review the prior colonoscopy report for bowel prep quality and whether the adenoma was completely removed; if prep was poor, repeat sooner.
2. Does she meet criteria for genetic evaluation?
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Probably not on the information given. Lynch syndrome assessment requires a cluster of cancers-often three relatives with Lynch-spectrum cancer, two successive generations, and one diagnosis before age 50-or a first-degree relative with a known mutation. She has two relatives with colon cancer at 52 and 60, no endometrial or ovarian cancer, and no young-onset case under 50. That does not clearly meet Amsterdam or Bethesda criteria. However, a first-degree relative with colon cancer before 60 is enough to discuss risk and to ask whether her father’s tumor was tested for mismatch repair deficiency. If he had abnormal testing, if more family members are diagnosed, or if she develops endometrial cancer, refer for genetic counseling. Do not order broad panel testing without counseling.
3. What would you tell her about stool DNA testing?
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Stool DNA testing is approved for average-risk screening every 3 years, not for surveillance after an adenoma or for a strong family history. It detects cancer reasonably well but is less sensitive for advanced adenomas, which are the lesions we are trying to remove before they become cancer. A positive result still requires colonoscopy, and a negative result does not rule out a polyp. For her, colonoscopy is the better test because it can remove lesions and because her risk is above average. If she refuses colonoscopy, annual FIT is a better alternative than stool DNA, but neither is equivalent. Document the discussion and the reason for her choice.