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Cancer Genetics

Genetic Testing Based on Adenoma

05/19/2006

Question:

My husband was just discovered to have 35+ adenomas. The doctor lost count after 35, but it is not more than 50. 9 were suspected for possible risk due to size and look, but upon biopsy have turned out to be 5 tubular and 4 tubulo villous benign polyps. He only has his mother diagnosed with stage 2 cancer at age 67 among his relatives.A digestive CT scan is negative and CEA is at normal level. Is there still a need for genetic testing or is it conclusive to say that he is Attentuated FAP? Is colectomy required or can he just have all 35+ polyps taken out via 3-4 colonoscopy procedures, to be followed by annual colonoscopy? Appreciate advise. THanks very much.

Answer:

Based on the information you give in your question, your husband could have an inherited cancer susceptibility syndrome.  You mention attenuated FAP, and this could be one possible explanation.  You mention that his mother had colon cancer at age 67, but there is no indication whether she had colon polyps or how many.  This information would be helpful if you decide to see a medical geneticist or genetic counselor.  Even though his CEA (a blood serum screening marker for colon cancer) is normal, and a CT scan is normal, this does not mean your husband is not at risk for developing colon cancer.  In fact, based on the number of polyps and the type of polyps found, he should continue with regular screening.

Colon cancer is usually thought to begin as a polyp that eventually becomes cancerous.  Not all polyps progress at the same rate to become cancerous, so it is important to be aware of the type of polyps found.  For example, hyperplastic polyps are the least likely (and some would say are unlikely) to become cancerous, while tubulovillous polyps have a greater likelihood be become cancerous.  You report that your husband had both tubular and tubullovilllous polyps.  He should discuss with his gastroenterologist an appropriate screening interval and follow this closely.

As for possible inherited causes of multiple polyps (or polyposis), we have learned that there are at least two genes that can predispose a person to develop multiple polyps: one gene is called the APC gene, and mistakes in this gene cause either familial adenomatous polyposis (FAP: a condition in which persons develop hundreds or thousands of polyps) and attenuated FAP (in which a person develops less than 100 polyps).  FAP and attenuated FAP are inherited in an autosomal dominant manner, so typically (but not always), a person with one of these conditions will have relatives in previous generations with colon cancer as well, and usually before the age of 50.

The second gene is called the MYH gene, and it can predispose individuals to as few as 10 and up to thousands of colon polyps.  It is inherited in an autosomal recessive manner, meaning that a genetic mistake must be inherited from each parent, but that the parents may not (and usually will not) develop colon cancer. 

And there are a number of individuals who develop numerous polyps who are not found to have detectable mutations in either gene.  These people may have mutations in genes we have not identified yet.

So, even though your husband has "attenuated FAP," it might be important for his siblings, and especially for his children, to know what the underlying cause of the AFAP is.  It is also relevant for your husband with regard to other cancers he may be at increased risk for.  My suggestion is to talk with a genetic counselor and with your husband's gastroenterologist to discuss how this information might be helpful.

As for whether he should continue to have regular colonoscopies, or should have his colon removed, this is a discussion he needs to have with his gastroenterologist.  The number of polyps that are found at each colonoscopy, the frequency of the colonoscopies and the size of the polyps, as well as the discomfort and risk associated with regular colonoscopies should be taken into account in making this decision.  Each doctor and each patient will have different perceptions of the best course of action to take in a situation such as this.

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Response by:

Duane D Culler, PhD, MS Duane D Culler, PhD, MS
Clinical Instructor of Genetics
School of Medicine
Case Western Reserve University