Researchers do not yet know the full story of what causes colorectal cancer. But they do know of several risk factors for the disease. They also know that cancers of all kinds begin when DNA inside our cells changes. DNA is a cellular chemical making up our genes, controlling how our cells work. We get our DNA from our parents.
Two types of genes control cell growth, division to make new cells and death. Oncogenes control cell growth, division and health. Tumor suppressor genes keep cell division controlled and cause cells to die when they should.
Some DNA mutations affecting oncogenes or tumor suppressor genes cause cells to grow uncontrolled, leading to cancers like colorectal cancer. These gene mutations are either inherited from our parents or acquired during our lifetime.
Some DNA mutations passed through generations of your family change cells in your body. These inherited mutations cause some colorectal cancers.
Colon cancers familial adenomatous polyposis (FAP) and Gardner syndrome begin from inherited changes in your APC gene, a tumor suppressor gene. A healthy APC gene keeps cell growth at a healthy pace. A mutated APC gene turns off its control of cell growth, leading to growth of hundreds of polyps in the colon. Cancer almost always develops from these polyps because there are the polyps’ cells contain mutations, too.
Lynch syndrome begins from gene mutations stopping cell repair of damaged DNA. DNA damage remains, sometimes affecting genes regulating growth and leading to development of cancer.
Peutz-Jeghers syndrome starts from inherited mutations in a tumor suppressor gene. This type of colon cancer causes benign polyps in the colon and hyperpigmentation on the lips and in the mouth.
MUTYH-associated polyposis starts from MUTYH gene mutations. This gene helps the cell check the accuracy of DNA during cell division. MUTYH-associated polyposis causes growth of multiple polyps in the colon that typically lead to colon cancer, in more than 43 percent of cases.
Genetic testing finds gene mutations causing inherited syndromes like these. If your family history includes colorectal polyps, cancers or these syndromes, genetic testing and genetic counseling help you understand your risk.
Some gene mutations occur after you are born. This means your parents did not pass these mutations down to you. These mutations only affect cells developed from a mutated dividing cell. Most colorectal cancers come from these types of DNA mutations. Researchers still have a lot to learn about acquired gene mutations and cancers.