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Colon Cancer Causes, Symptoms, and Treatments

Colon cancer (or colorectal cancer) is one of the most common cancers in the U.S. It happens when growths (polyps) in your colon turn malignant.

Blood in your stool and changes in bowel habits are common signs of colon cancer.

Treatment for colon cancer may include surgery, chemotherapy, or radiation therapy.

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What Is Colon Cancer?

Doctors define colon cancer as a disease where once harmless polyps become malignant. These polyps occur in the lining of the colon and rectum.

The colon is the first and longest part of the large intestine. It absorbs water and nutrients from the food you eat and changes the waste that's left over into stool. Your body stores stool in the rectum, which is the lower part of the large intestine.

Colorectal cancer is the 3rd most common cancer in the U.S. (besides skin cancer).

Anyone can get colon cancer, but it's more common among older people. The lifetime risk of getting colorectal cancer is about 1 in 23 for men, and 1 in 26 for women.

Because colon cancer is slow growing, early diagnosis can often lead to a complete cure. Screening tests like colonoscopies are crucial because they can catch colorectal cancer in its early stages, before you notice symptoms.

What are the types of colon cancer?

The most common type of colon cancer is an adenocarcinoma. These abnormal growths account for up to 95% of colon tumors.

Adenocarcinomas start as polyps in the lining of the bowel wall, in the cells that produce mucus.

Other types of cancer can affect the colon, but they're rare.

They include:

  • Carcinoid tumors. These slow-growing tumors begin in hormone-producing tissue of the digestive system.
  • Melanomas. Usually associated with skin cancer, these cancers may spread from elsewhere in the body.
  • Sarcomas. These cancers start in the smooth muscle of the colon.
  • Squamous cell tumors. These tumors may begin in the skin cells of the bowel lining or spread from elsewhere in the body.

What causes colon cancer?

Nearly all colon cancers start as benign (noncancerous) polyps and slowly turn into cancer. Doctors aren't sure what triggers the change.

It may be that genes mutate and cause colon cancer. These changes to your DNA might happen during your lifetime, or you may be born with them.

What are colon cancer risk factors and complications?

Colon cancer risk factors

Although the exact cause of colon cancer may be unclear, certain risk factors increase your chances of getting it.

You have a higher risk of getting colon cancer if you:

  • Are obese.
  • Are African American or of eastern European descent.
  • Are over 45 years old.
  • Drink more than three alcoholic drinks per day.
  • Eat a diet high in red meat and fat, and low in fiber, fruits, and vegetables.
  • Have a family history of colon or rectal cancer, or inflammatory bowel disease (IBD).
  • Have a genetic syndrome such as familiar adenomatous polyposis (FAP).
  • Have chronic ulcerative colitis or Crohn's disease.
  • Have colon polyps.
  • Smoke.

Complications of colon cancer

Colon cancer can lead to other health issues, including:

  • Anemia.
  • Bowel obstruction, if the tumor blocks the intestines.
  • Cancer spreading to other tissues or organs.

How can I reduce my risks of colon cancer?

To reduce your risk of getting colon cancer, you should:

  • Eat a diet rich in whole grains, fruits, and vegetables.
  • Exercise a few times a week.
  • Get routine screenings for colon cancer.
  • Have polyps removed before they can turn into cancer.
  • Limit alcohol.
  • Maintain a healthy weight.
  • Quit smoking.

Why choose UPMC for colon cancer care?

When you come to UPMC for colon cancer care, you'll see some of the world's most highly trained experts.

Your health care team may include:

  • Colon and rectal surgeons.
  • Highly skilled nurses.
  • Pathologists.
  • Radiation and medical oncologists.
  • Radiologists.

These cancer experts work together to create a custom treatment plan for you.

Colon Cancer Symptoms and Diagnosis

What are the signs and symptoms of colon cancer?

Colon cancer doesn't tend to cause symptoms at first. You may not see colon cancer signs until the disease is more advanced.

Warning signs of colon cancer include:

  • Bleeding from your rectum or blood (bright red or very dark) in your stool.
  • Changes in bowel habits that last more than a few days, such as frequent constipation or diarrhea.
  • Fatigue or weakness.
  • Feeling like your bowels don't empty all the way.
  • Frequent gas, bloating, cramps, or other belly pain.
  • Stool that looks different than usual (it's narrow or the shape differs).
  • Weight loss you can't explain.

How do you diagnose colon cancer?

Colon cancer has few — if any — symptoms in the early stages.

The best way to catch colon cancer early is through colon cancer screening. Routine screenings can uncover signs of disease before symptoms occur. If doctors catch colon cancer early, it's often easier to treat.

Your doctor will likely advise screening for colon cancer from about age 45 to 75.

Screening tests include:

  • Colonoscopy.
  • Flexible sigmoidoscopy.
  • Stool tests.

If your screening test is abnormal, or if you have symptoms of colon cancer, your doctor will order more tests.

These may include:

  • A complete physical exam.
  • Blood tests.
  • CT or MRI scans.

What Are the Treatment Options for Colon Cancer?

Your treatment may depend on the stage of the disease.

Your care team may suggest one or more of the following:

  • Chemotherapy to kill cancer cells.
  • Immunotherapy to destroy cancer cells. This treatment uses substances made by the body (or in a lab) to boost your body's immune system.
  • Radiation therapy in select cases of rectal cancer.
  • Surgery to remove part of the colon or rectum.
  • Targeted therapy, which uses substances that attack cancer cells but cause less harm to normal cells.

Colectomy surgery for colon cancer

Colectomy is often the first and main treatment for most people with colon cancer.

Surgeons remove the part of the colon at the cancer site and nearby tissues at risk of harboring cancer cells. This also includes the adjacent lymph nodes and any tissue attached to the cancer.

In nearly all cases, the surgeon then joins the bowel together, also known as anastomosis.

Colon cancer stages

To learn the stage of colon cancer, your surgeon will send samples to a lab for an assessment.

Knowing the stage is vital because it lets your doctors determine the likelihood of tumor recurrence.

Based on that assessment, they may advise some people to have further chemo treatment.