What is hereditary mixed polyposis syndrome?

Hereditary mixed polyposis syndrome (HMPS) is a hereditary condition that is associated with an increased risk of developing polyps (growths of normal tissue that form lumps) in the digestive tract. As the name suggests, a variety of polyps may occur. The most common polyp type is the hamartomatous juvenile polyp. A hamartoma is a growth of normal-appearing tissue that builds up into a noncancerous tumor. However, the growth can turn into cancer over time. Adenomatous polyps (growths in the lining of the colon that can become cancerous) and hyperplastic polyps (noncancerous growths in the lining of the colon) may occur as well. People with HMPS also have an increased risk of developing colorectal cancer. Little is currently known about HMPS, but more information is likely to become available in the future.

What causes HMPS?

HMPS is a genetic condition. This means that the risk of polyps and cancer can be passed from generation to generation in a family. There is currently no specific gene that has been identified to cause HMPS.

How is HMPS inherited?

Normally, every cell has two copies of each gene: one inherited from the mother and one inherited from the father. HMPS is believed to follow an autosomal dominant inheritance pattern, in which a mutation needs to happen in only one copy of the gene for the person to have an increased risk of getting that disease. This means that a parent with a gene mutation may pass along a copy of their normal gene or a copy of the gene with the mutation. Therefore, a child who has a parent with a mutation has a 50% chance of inheriting that mutation. A brother, sister, or parent of a person who has a mutation also has a 50% chance of having the same mutation.

How common is HMPS?

HMPS is considered to be rare.

How is HMPS diagnosed?

There are no specific diagnostic criteria for HMPS. HMPS is suspected in individuals and families with a history of multiple colon polyps of different types. It is also important to consider the possibility of one of the other hereditary polyposis syndromes, such as familial adenomatous polyposis, Peutz-Jeghers syndrome, and juvenile polyposis syndrome. There is currently no blood test that can help diagnose HMPS.

What are the estimated cancer risks associated with HMPS?

People with HMPS are considered to be at increased risk for developing colorectal cancer, but the amount of risk has not been estimated.

What are the screening options for HMPS?

There are no specific screening guidelines developed for HMPS. Regular screening colonoscopies are appropriate. Many doctors would suggest beginning screening five to 10 years earlier than the youngest age at which polyps were identified in a family member. If polyps are found, screening may need to be done as often as once a year.

Screening options may change over time as new technologies are developed and more is learned about HMPS. It is important to talk with your doctor about appropriate screening tests.

To learn more about what to expect during common diagnostic tests, read Cancer.Net: Tests and Procedures.

Questions to ask the doctor

If you are concerned about your risk of colorectal cancer or other types of cancer, talk with your doctor. Consider asking the following questions of your doctor:

• What is my risk of developing colorectal cancer?
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• How many colon polyps have I had in total?
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• What types of colon polyps have I had? (the most common types are hamartomatous juvenile, hyperplastic, and adenomatous)
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• What is my risk of other types of cancer?
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• What can I do to reduce my risk of cancer?
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• What are my options for cancer screening?

If you are concerned about your family history and think your family may have HMPS, consider asking the following questions:

• Does my family history increase my risk of colorectal cancer or other types of cancer?
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• Should I meet with a genetic counselor?
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• Should I consider genetic testing?

Additional resources

Cancer.Net Guide to Colorectal Cancer

The Genetics of Colorectal Cancer

What to Expect When You Meet With a Genetic Counselor

Colon Cancer Alliance
www.ccalliance.org

National Cancer Institute
www.cancer.gov

American Cancer Society
www.cancer.org

CancerCare
www.cancercare.org

To find a genetic counselor in your area, ask your doctor or visit the following websites:

National Society of Genetic Counselors
www.nsgc.org

National Cancer Institute: Cancer Genetics Services Directory
www.cancer.gov/search/geneticsservices