Colorectal cancer is a type of cancer that occurs in the colon (large intestine) and rectum. Colorectal cancer often starts as noncancerous polyps, which are clumps of cells that can turn into cancer in some cases.

According to the American Society of Clinical Oncology (ASCO), colorectal cancer is the third most commonly diagnosed cancer. It’s the third leading cause of cancer death in the United States.

Screenings and early detection of colorectal cancer can improve your chances of surviving this type of cancer.

Most cases of colorectal cancer begin as a type of polyp called an adenoma. These polyps are noncancerous, but can turn into cancer.

In many cases, doctors don’t know what causes the polyps or what causes them to turn into cancer. However, there are genes that can increase your risk of colorectal cancer. These genes cause a small percentage of colorectal cancers but significantly increase risk.

Genetic conditions that increase your risk for colorectal cancer include:

Familial adenomatous polyposis

People with familial adenomatous polyposis (FAP) develop hundreds to thousands of polyps in their colon and rectum. Polyps can start developing as early as someone’s teenage years, and will become cancerous if not removed. The number of polyps generally increases with age, and the average age of colorectal cancer onset is 39.

There’s also a type of FAP called attenuated FAP, in which polyps don’t start developing until later. The average age of colorectal cancer onset for people with this form of FAP is 55. Both classic and attenuated FAP are caused by mutations on the APC gene.

A third type of FAP is autosomal recessive familial adenomatous polyposis, which is a milder form. People with this form develop fewer polyps. It’s caused by a different genetic mutation than other types of FAP.

Lynch syndrome

Lynch syndrome increases your risk of colorectal cancer, as well as endometrial, ovarian, gastric, urinary tract, brain, and pancreas cancers. An estimated 3 percent of colon cancers are caused by Lynch syndrome.

People with Lynch syndrome often develop colon cancer before age 50. They may have a family history with a lot of people who had cancer, especially colon cancer. Lynch syndrome is caused by a dominant gene mutation, which means you only need to inherit the mutation from one parent to develop the condition.

MYH-associated polyposis

MYH-associated polyposis caused polyps in the colon and rectum, similarly to the milder form of FAP. It’s a recessive trait, which means you have to inherit a mutation in the MYH gene from both parents to develop MYH-associated polyposis. Research on this condition is still in early stages but suggests that it can significantly increase risk for colorectal cancer.

There’s also a type of hereditary colon cancer called hyperplastic polyposis syndrome. It causes hyperplastic polyps, which are usually benign, but also greatly increases your risk of colorectal cancer. Research is in early stages, and right now, there’s no known gene associated with this syndrome.

colorectal cancer FACTS

Lifestyle factors, including weight, diet, and exercise may increase your risk of developing colorectal cancer. Age is also a risk factor.


Several components of a Western diet have been shown to increase your risk of colorectal cancer. Specifically, diets high in fat and low in fiber are associated with an increased risk of colorectal cancer.

Red and processed meats have been shown to increase risk of colorectal cancer. Cooking the meat at high temperatures may increase the risk even further.

High fiber foods — including fruits, vegetables, and grains — may decrease your risk of colorectal cancer. Many of these foods are also rich in vitamin B, which may also decrease colorectal cancer risk.


Colorectal cancer is one of the many diseases where regular exercise may decrease your risk. The American Institute of Cancer Research recommends 2.5 hours of moderate physical activity a week.

Regular exercise after a colorectal cancer diagnosis may also improve survival rates. It may also decrease the risk of reoccurrence.

Alcohol consumption

Reducing alcohol consumption may decrease your risk of developing colorectal cancer (and other cancers).


People who smoke have an increased risk of colorectal cancer.


Colorectal cancer is rare in people under 50 who do not have a genetic condition associated with it. The risk increases as you get older.


Being obese is associated with a higher risk of colorectal cancer, especially for men.

Chronic inflammatory conditions

People with chronic inflammation conditions that affect their colon, such as Crohn’s disease and ulcerative colitis, can have an increased risk of colon cancer.

To reduce your risk of developing colorectal cancer:

  • Get screened regularly if you are older than 50 or at an increased risk.
  • Eat a diet rich in fruits, vegetables, and whole grains. Eating a wide variety of these foods can reduce your risk even further.
  • Get most of your protein from poultry, fish, or legumes instead of red or processed meat.
  • Don’t smoke.
  • Drink alcohol in moderation.
  • Maintain a healthy weight.
  • Exercise regularly (at least 30 minutes 5 days a week).

Many people with early colorectal cancer don’t have any symptoms. Therefore, it’s important to be regularly screened if you’re over 50 years old or at increased risk. There are several different tests that can help doctors screen for and diagnose colorectal cancer.


Your doctor may use a scope — a camera on a thin, flexible tube to look at your colon and rectum. There are two types:

  • Colonoscopies. Everyone who is between 50 and 75 years of age and at normal risk for colorectal cancer should have a colonoscopy every ten years. Colonoscopies allow your doctor to see your entire colon and remove polyps and some cancers. It’s also used as a follow-up to other tests when necessary.
  • Sigmoidoscopy. This uses a shorter scope than a colonoscopy does and lets doctors view your rectum and the lower third of your colon. If you choose to have a sigmoidoscopy for screening, it should be done every five years, or every ten years if you get a fecal immunochemical test every year.

Stool tests

In addition to scopes, there are tests that look at your stool for signs of colorectal cancer. These include:

  • Guaiac-based fecal occult blood test (gFOBT). Uses a chemical to detect blood in your stool. You get a kit from your doctor, collect stool at home, then return the kit for analysis.
  • Fecal immunochemical test (FIT). Similar to a gFOBT, but uses antibodies to detect blood in stool.
  • FIT-DNA test. Combines the FIT with a test for altered DNA in your stool.

Symptoms of colorectal cancer include:

  • rectal bleeding or blood in your stool
  • unexplained weight loss
  • diarrhea, constipation, or other bowel changes that last at least four weeks
  • long-lasting abdominal discomfort or pain, such as cramps
  • weakness and fatigue
  • tenderness in your lower abdomen

Some cases of colorectal cancer are due to genetic factors, but in many others, doctors do not know the cause. And because early stage colorectal cancer often doesn’t cause any symptoms, early detection is essential. When detected early, colorectal cancer can be treatable and curable.