Colorectal cancer is a disease in which malignant (cancer) cells form in the tissues of the colon or the rectum.

The colon and rectum are parts of the body's digestive system. The digestive system removes and processes nutrients (vitamins, minerals, carbohydrates, fats, proteins, and water) from foods and helps pass waste material out of the body. The digestive system is made up of the mouth, throat, esophagus, stomach, and the small and large intestines. The first 6 feet of the large intestine are called the large bowel or colon. The last 6 inches are the rectum and the anal canal. The anal canal ends at the anus (the opening of the large intestine to the outside of the body).

Anatomy of the lower digestive system, showing the colon and other organs.

Cancer that begins in the colon is called colon cancer, and cancer that begins in the rectum is called rectal cancer. Cancer that begins in either of these organs may also be called colorectal cancer.

Colorectal cancer is the second leading cause of death from cancer in the United States.

In recent years (1995-1999), the number of people diagnosed with colorectal cancer has stayed about the same, but the number of people who die from colorectal cancer has decreased. Colorectal cancer is found more often in men than in women.

Studies show that screening for colorectal cancer decreases the number of deaths from this disease.

Age and health history can affect the risk of developing colon cancer.

Anything that increases a person's chance of getting a disease is called a risk factor. Risk factors for colorectal cancer include the following:

• Being older than 50 years of age.
• Having a personal history of any of the following:
  • Colorectal cancer.
  • Polyps in the colon or rectum.
    
    Polyps in the colon. Some polyps have a stalk and others do not. Inset shows a photo of a polyp with a stalk.
  • Cancer of the ovary, endometrium, or breast.
  • Ulcerative colitis or Crohn disease.
• Having a parent, brother, sister, or child with colorectal cancer or polyps.
• Having certain hereditary conditions, such as familial adenomatous polyposis (FAP) and hereditary nonpolyposis colon cancer (HNPCC; Lynch Syndrome).

Refer to the PDQ summary on Genetics of Colorectal Cancer for more information about family history and colorectal cancer screening.