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Colon & Rectal Cancers

The Genetics of Colon and Rectal Cancers

You may have heard that many cancers have a genetic factor. However, most are not considered hereditary in colon and rectal (colorectal) cancers, meaning that it isn't passed down from one family member to another. Research indicates that an inherited gene mutation causes only about 5% of all colorectal cancers. The remaining 95% are caused by a mutation of a gene acquired during a person's lifetime (non-genetic).

Inherited Gene Mutations Connected to Colorectal Cancer

Cancer is caused by genetic changes that may result in cancer or tumors. Some of these mutations, called inherited (hereditary) mutations, are the type that can be passed from one family member to the next. These mutations exist in the body throughout a person's life. They are also found in almost every cell of the body. Common genetic syndromes, which are disorders caused by one or more abnormalities in the genome, have been linked to colorectal cancer. Some of these syndromes may include:

  • Lynch syndrome (hereditary non-polyposis colon cancer, or HPCC): caused by changes in genes that help damaged DNA repair itself. Mutations of genes like MLH1, MSH2, MLH3, MSH6, PMS1, and PMS2 keep DNA errors from being fixed. This can affect growth-regulating genes and can lead to the development of cancer.
  • Familial adenomatous polyposis (FAP) and Gardner syndrome: caused by inherited changes in the APC gene, which is a tumor suppressor gene that helps keep cell growth in check. Changes in the APC gene may lead to the growth of polyps in the colon. While not all polyps are cancerous, some can be.
  • MUTYH-associated polyposis: caused by mutations in the MUTYH gene, which plays a role in how the cell checks the accuracy of DNA when cells divide.
  • Peutz-Jeghers syndrome: caused by inherited changes in the tumor-suppressor gene STK11 (LKB1).

Acquired Gene Mutations and Colorectal Cancer

Some mutations may just happen throughout a person's life and don't have a genetic link at all. While inherited mutations can impact the whole body, acquired gene mutations affect cells from the original cell mutation. Research indicates that it isn't exactly known what causes this type of gene mutation. However, some factors may put you at higher risk, such as:

  • Smoking
  • Poor diet
  • Exposure to UV radiation

Genetic Testing for Colorectal Cancer

There are some indicators known to be related to genetic mutations that cause cancers. Learn more about who is likely to qualify for genetic testing. These tests can also show whether family members who may not have any symptoms inherited the same mutation as a family member who carries a cancer-associated mutation. The results of these tests will let you know if you are in a high-risk category for developing colorectal cancer or other types of cancers. Knowing these results may help your doctor determine when you should start various regular colorectal cancer screening tests.

Factors that suggest a genetic contribution to colorectal cancer include:

  • A family history of colorectal cancer and/or polyps
  • Early age at diagnosis
  • Multiple cancers in a patient with colorectal cancer

Based on these factors, your doctor may recommend genetic testing. Knowing the results of these tests will help you make other plans regarding your health and future. However, genetic testing can be a sensitive topic for some people. Talk with your family members about whether they want the results shared with them before you speak to them about your results. Not everybody feels the same way about knowing genetic testing data. These conversations can be difficult, and choosing to complete genetic testing can be a hard decision to make. For more help and support, genetic counseling is available for people who are considering this type of testing.

Genetic Testing in Brevard County, Florida


Cancer Centers of Brevard provides genetic testing and colon cancer treatment in Melbourne, Palm Bay, Rockledge, and Merritt Island. If you feel you may be at a higher risk of developing cancer based on your family history, contact our genetic counseling team. We are happy to answer your questions and schedule an appointment.