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What Causes Colorectal Cancer?

Colorectal cancer does not usually have a clear cause. There are inherited gene mutations that can put you at higher risk for colorectal cancer, and there are risk factors that are thought to increase your chances of developing cancer. We do know that most colon cancers develop from polyps on the lining of the colon or rectum.

Inherited Gene Mutations

A small percentage of people who develop colorectal cancer have a gene mutation that was inherited by their parents. People with these gene mutations make up about 7 percent of people who develop colorectal cancer. 

These gene mutations increase the risk of developing colon cancer. Not everyone with these mutations will get cancer, but they have a significantly greater risk of developing cancer than people without the gene mutation.

There are two common gene mutations, known as inherited colon cancer syndromes. 

  • Hereditary nonpolyposis colorectal cancer (HNPCC) – HNPCC increases the risk for several cancers, including colorectal cancer. It is also known as Lynch syndrome. People with this genetic mutation tend to develop colorectal cancer before the age of 45. If anyone in your family has this genetic mutation, you may want to be tested for it. If you have the mutation, your doctor will recommend colonoscopy screenings start early – at age 25 or 5 years earlier than your family member’s age at diagnosis of cancer, whichever is earlier. People with this syndrome have a 70 to 80 percent lifetime risk of developing colorectal cancer.
  • Familial adenomatous polyposis (FAP) – FAP is a rare genetic disorder that causes thousands of polyps to develop in the lining of the rectum and colon. It is caused by a defect in the APC gene. (APC stands for adenomatous polyposis coli.) Most people with FAP inherited it from a parent, but the gene mutation can also occur spontaneously. 
  • People who have FAP and don’t receive treatment have a significant risk of developing colon cancer before their 40th birthday, and often the polyps will begin growing during the early teen years (if not before). Therefore, it is vital to have colonoscopies starting at a young age. Most doctors recommend that children who have the genetic mutation begin screenings at age 10. If children have a parent or sibling with the mutation, but they don’t have the mutation themselves, screenings should begin at age 15.

If you have a family history of colorectal cancer or of any gene mutation that is linked to an increased risk of colorectal cancer, you can be tested to find out whether you also have that gene mutation. Call (248) 577-9277 to get a referral to a geneticist who can help you decide what steps to take.

Risk Factors for Colorectal Cancer

Anyone can get colorectal cancer, but there are risk factors that increase the odds that you will develop cancer.

Some of those risk factors are:

  • Age – While anyone at any age can get colorectal cancer, most people who develop it are over age 45.
  • Gender – Men are slightly more likely than women to develop colorectal cancer.
  • A personal history – If you have had colon polyps or colorectal cancer in the past, you have an increased risk of developing cancer again.
  • A family history – If you have a parent, child, or sibling who has had colorectal cancer, you are at higher risk of developing it too.
  • Inflammatory conditions – There are inflammatory bowel conditions, like Crohn’s disease and inflammatory bowel disease (IBD), that put you at higher risk. 
  • A genetic mutation – Having certain gene mutations put you at higher risk (see the gene mutations section above for more information). 
  • A high-fat, low-fiber diet – Studies have shown that a “Western diet” high in fat and low in fiber can increase risk of developing colon cancer. 
  • Being overweight – Obesity is a risk factor for colorectal cancer. 
  • Drinking alcohol – Drinking more than one alcoholic beverage per day can put you at higher risk for developing colorectal cancer.
  • Smoking – Smoking puts you at risk for colorectal and many other cancers.
  • A sedentary lifestyle – People who don’t get enough exercise are at higher risk.
  • A history of receiving radiation for cancer treatment – Radiation treatment can damage healthy cells and may increase a person’s risk for future cancer.

Some risk factors cannot be changed, such as age, race, gender, and gene mutations. But there are risk factors within your control. You can adopt or maintain a healthy lifestyle to help reduce your risk of getting colorectal cancer. Eating a high-fiber diet full of fruits and vegetables and limiting your consumption of red meat, processed foods, foods high in saturated fat, and alcohol; getting to and maintaining a healthy weight; exercising every day; and not smoking are a few things you can do to reduce your risk. Most importantly, however, you can take control of your risk of developing colon cancer by getting your recommended colonoscopies. This is the most important and effective way to prevent colorectal cancer.


Learn more about what you can do to prevent colorectal cancer.


If you’re over 45, we recommend scheduling a screening colonoscopy – whether you have risk factors or not. If you do have risk factors, such as a family history, you may need your screening colonoscopy earlier. Ask your doctor when the right time is for you to have yours. 

Call (800) 633-7377 today to ask for a referral for your colorectal cancer screen, and take control of your bowel health.