Colon and Rectal Cancer

Your colon, or large intestine, connects your small intestine to your rectum. Averaging around five feet in length in adults, the colon is made up of five separate segments. Colorectal cancer can develop in any of these areas, including the rectum.

Colorectal cancer usually starts as polyps—a clump of cells or tissue—in the inner lining of your colon or rectum. Polyps can range in size from a small dot to several inches. Most polyps, which are discovered through a preventive and diagnostic test called a colonoscopy, are not cancer. If your doctor finds a polyp during this test, they’ll remove it and have it tested by a pathologist to see if it contains abnormal cells. Abnormal cells could indicate cancer.

About 95% of colorectal cancers are adenocarcinomas, or a cancer that starts in the lining of an organ. Colorectal cancer can invade deeper into the tissue, which is called advanced disease. Cancer cells can also spread to other areas of the body, called metastasis.

The American Cancer Society recommends that people with average risk for colorectal cancer begin regular screening starting at age 45, while other national guidelines recommend that screening start at age 50. Because it can take 10 to 15 years for cancer to develop, you should have a colonoscopy every 10 years if the results of the first colonoscopy are normal. New sensitive stool- and blood-based tests are also available.

Risk Factors

The American Cancer Society estimates that about 105,000 people are diagnosed with colon cancer and 43,000 people are diagnosed with rectal cancer in the US each year. The average person’s lifetime risk for developing this cancer is about 1 in 25 (4%). This risk is slightly lower in women than in men.

Because most risks for colorectal cancer are out of your control, it is not your fault if you’re diagnosed with cancer. Race, age, and medical history can increase your risk.

Can you prevent getting colorectal cancer? While most colorectal cancer is caused by factors you can’t change, you can do these things that have been shown to reduce colorectal cancer risk in general:

  1. Decrease red meat and processed meats like hot dogs and lunch meats from your diet
  2. Increase vegetables and whole grains in your diet
  3. Stop smoking
  4. Make lifestyle changes to decrease your body weight
  5. Limit your alcohol intake
  6. Increase your physical activity

Risk Factors for Colorectal Cancer


African Americans have a high rate of colorectal cancer. Jewish people of Eastern European descent (Ashkenazi Jews) have a gene mutation that also puts them at a high risk for this cancer type.


Nearly nine out of 10 people who are diagnosed with colorectal cancer are 50 or older. However, rates of colorectal cancer are declining in people 50 and older, in part due to prevention via the removal of precancerous polyps during screening colonoscopy. Though colorectal cancer is less common in people younger than 50, rates in this age group are rising.

Personal History of Colorectal Polyps or Colorectal Cancer

If you have large polyps or many of them, this is especially true.

Personal History of Inflammatory Bowel Disease (IBD)

IBD, including ulcerative colitis and Crohn’s disease, causes long-term inflammation in your colon. People with these conditions should be screened for colorectal cancer at an earlier age and more often.

Family History of Colorectal Cancer or Adenomatous Polyps

Most colorectal cancer happens in people with no family history. But about 20% of people who have a family member who had adenomatous polyps have a higher risk of developing colorectal cancer.

Inherited Syndromes

About 5–10% of people who get colorectal cancer have inherited gene problems, called mutations. The most common mutations are familial adenomatous polyposis (FAP) and hereditary non-polyposis colorectal cancer (HNPCC). If you have one of these mutations, you may develop colorectal cancer earlier in life. You may also be at risk for other types of cancer. For instance, people with HNPCC are also at risk for uterine cancers [LINK]. If you have several family members with colorectal cancer, or if you’re diagnosed at a young age, you should consider having a genetics risk assessment and counseling.

Rare Inherited Conditions

Turcot syndrome, Peutz-Jeghers syndrome, and MUTYH-associated polyposis can also increase your risk.

Type II Diabetes

People with type II or non-insulin dependent diabetes have an increased risk of developing colorectal cancer and a less favorable outlook after diagnosis.

Lifestyle Factors

Poor diet—not enough vegetables, fruits, and whole grains, but a lot of red and processed meat—contributes to colorectal cancer risk. So does a sedentary lifestyle, obesity (especially for men), smoking, and excessive alcohol drinking.

Signs of Colorectal Cancer

Often there are no obvious signs of colorectal cancer, but some symptoms can include:

  • Change in bowel habits or frequency, such as alternating episodes of diarrhea and constipation
  • Bloody bowel movements or rectal bleeding
  • General abdominal discomfort
  • Unexplained weight loss
  • Chronic fatigue
  • Bloating
  • Unexplained anemia

Screening and Diagnosis

Nearly all cases of colorectal cancer begin with the growth of polyps, or benign growths of tissue, in the intestine. If these growths are detected and removed early, the development of colorectal cancer can be prevented. A highly sensitive test of your stool can also find abnormalities early.

The American Cancer Society recommends that you start screening when you’re 45. If you have a family history, it is recommended that you begin screening 10 years before the age at which your family member was diagnosed, even if no genetic mutation was found.

Types of Tests

There are several types of colorectal cancer screening and diagnosis tests. They can be done alone or in combination. The most commonly recommended screening test is a colonoscopy, and if that is not possible, a fecal occult blood test. You should talk to your doctor about which method is right for you.

  • Fecal occult blood test (FOBT) checks for hidden blood in your stool.
  • Flexible sigmoidoscopy uses a flexible lighted tube to examine the inside of your rectum and lower third of your large bowel. Your doctor might remove polyps and collect tissue samples (biopsy) to take a closer look. About 65% of precancerous polyps are found here.
  • Colonoscopy uses a flexible, lighted tube to look at the inside of your rectum and your entire colon, from your anus to the junction of your colon and small intestine Your doctor may remove polyps and collect tissue samples (biopsy) for closer examination.
  • Double contrast barium enema uses a dye barium, followed by an injection of air and X-rays. The barium outlines the intestine on the X-ray so your doctor can see polyps and other abnormalities easier.
  • CT colonography or virtual colonoscopy is a noninvasive way to visualize your colon using a CT scan. A CT scan is a series of X-rays that come together to make a 3D image. This test’s main disadvantage is that abnormalities require you to have a regular colonoscopy or sigmoidoscopy for a biopsy.
  • Sigmoidoscopy allows examination of the lower third of the large bowel. About 65% of all precancerous polyps are found in this region. During colonoscopy, the entire colon is examined from the anus all the way to the junction of the small intestine and the colon.

You should speak with your doctor about the screening method that is right for you. These examinations are important not only to determine the extent of the current problem but also to look for other abnormalities, which could influence your best course of treatment.

You may also need additional tests, including:

  • Blood tests
  • An abdominal CT scan or MRI to determine if cancer has spread
  • A transrectal ultrasound, which uses sound waves to evaluate cancer and to determine the tumor’s depth and the degree of lymph node involvement.