Genetics and Colorectal Cancer

Genes are made up of DNA, the biochemical material that gives your cells directions on how to behave. You inherit your genes from your mother and father. In addition to determining how your cells work, genes determine what you look like, and may, unfortunately, make you more likely to get certain diseases.

It is probable that all cancers, especially colorectal cancers, have genetic factors that could increase a person’s chances of developing the disease. These genetic abnormalities, or mutations, are why certain types of cancer tend to occur more often in some families. It is very important that you provide your doctors with a detailed family medical history.

What are the types of colorectal cancers?

When it comes to whether or not genetics are a factor, there are three general categories of colorectal cancer.


“Sporadic” is the most common type; 80% of all colorectal cancers fall into this category. In these cases, the cancer appears to have occurred simply by chance. Most people in this group are over age 50 and do not have any family history of the disease.


When there are more cases of colorectal cancers in a family than chance alone would predict, but there is no specific genetic abnormality found, the disease is called “familial” colorectal cancer. Familial cancers account for 10% to 15% of colorectal cancers. It is not clear why some families have a higher rate of colorectal cancer, but theories include a shared lifestyle or environmental factors, and/or a combination of genes.

Regardless of the exact cause of the higher occurrence, anyone with a first-degree relative (parent, sibling, or child) who has, or has had, colorectal cancer, has twice the risk of developing colorectal cancer themselves. If you fall into this category, you should begin screening about 10 years before the age at which your relative was diagnosed with cancer, or age 40 – whichever occurs first.


Families with inherited colorectal cancer often have at least two generations that have had colorectal cancer that was caused by an inherited genetic mutation. These cancers tend to occur at younger- than-average ages (usually before age 50), and these people may also have a history of developing two (or more) types of cancer. Genetic testing can often be beneficial in determining who in the family has an increased cancer risk. In most cases, it is best to first test a relative who has cancer, to see if he or she carries a genetic mutation that is known to cause colorectal rectal. If so, then relatives who have not had cancer may be tested.

Some of the syndromes caused by identified abnormal genes include:

  • HNPCC (hereditary non-polyposis colon cancer, or Lynch syndrome)
  • FAP (familial adenomatous polyposis)
  • aFAP (attenuated familial adenomatous polyposis)
  • Peutz-Jehger’s Syndrome • MAP (MYH associated polyposis)
  • Juvenile polyposis
  • Hereditary polyposis

If genetic testing reveals any of these abnormalities, your family should talk to the genetic counselors at Roswell Park.

What should I tell my doctor and surgeon about my family history?

The following information will enable your doctor or surgeon to create the best plan for the prevention or treatment of colon cancer.

Tell your doctor if you have any:

  • personal history of any cancer
  • personal history of inflammatory bowel disease (ulcerative colitis, Crohn’s disease)
  • family members diagnosed with colorectal cancer or polyps – and their ages when the polyps or cancer occurred
  • first- or second-degree family members who have had cancer, and the type of cancer they had
  • other diseases that run in the family

Providing these details can help your doctors evaluate your risk and may help identify a cancer syndrome within your family. Your doctor may recommend that you take additional action to help identify if a familial cancer syndrome exists. For example, you may be asked to have a colonoscopy or genetic testing, receive genetic counseling, and/or have regularly scheduled exams.