Colorectal Cancer

Medically Reviewed by Minesh Khatri, MD on March 12, 2023
15 min read

Colorectal cancer, sometimes called colon cancer, starts when cells that line your colon or rectum grow out of control. It’s the third leading cause of cancer deaths among American men and women.

In the U.S., about 72% of colorectal cancer cases start in the colon and 28% in the rectum.

The colon is also called the large intestine, which is part of your digestive system. It absorbs water and nutrients from food after it moves through your stomach and small intestine. Solid waste (poop or stool) is stored in your colon before moving to the rectum. This 8-inch tube holds the waste until it leaves your body through the anus.

Most colorectal cancers are "silent" tumors. They grow slowly, and you may not notice any symptoms until they’re large. But you can take some steps to prevent colorectal cancer, and you can cure it if you find it early. It’s important to have regular screening exams to spot cancer or precancerous areas, especially if you have a high risk of getting it.

There are several types of colorectal cancer, based on where it starts.

  • Adenocarcinoma. This is the most common kind, making up 96% of cases. It starts in cells that make mucus for your colon and rectum.
  • Carcinoid tumor. This begins in cells that make hormones.
  • Gastrointestinal stromal tumor. This forms in cells in the wall of your colon that tell your gastrointestinal muscles to move food or liquid along.
  • Lymphoma. This is cancer of your immune system cells.
  • Sarcoma. This starts in connective tissues like blood vessels or muscle layers.

Nearly all colon and rectal cancers begin as a polyp, a growth on the inner surface of your colon. Polyps themselves usually aren’t cancer.

The most common types of polyps in your colon and rectum include:

  • Hyperplastic and inflammatory polyps. These usually don’t carry a chance of cancer. But large hyperplastic polyps, especially on the right side of your colon, can be a problem. Your doctor will want to remove them.
  • Adenomas or adenomatous polyps. These are precancerous. If you leave them alone, they could turn into colon cancer.

Colorectal cancer may also start in an area of abnormal cells, called dysplasia, in the lining of your colon or rectum.

Anyone can get colorectal cancer. It’s most common among African Americans and people over age 50.

The lifetime chance of developing colorectal cancer is 1 in 22 for men and 1 in 24 for women.

Things that can raise your chances of getting it include:

Polyps might be more likely to contain cancer or carry a higher chance of cancer if:

  • They’re larger than 1 centimeter
  • You have more than two
  • They show signs of dysplasia

You might not notice any signs of colorectal cancer. When you have them, they can include:

  • A change in your bowel habits that doesn’t go away, such as constipation or diarrhea
  • A feeling that your bowel hasn’t emptied all the way after you poop
  • Bleeding from your rectum
  • Blood on or in your poop
  • Poop that’s narrower or thinner than usual
  • Belly discomfort
  • Stomach cramps
  • Weight loss with no clear cause
  • An unusually low number of red blood cells (anemia)
  • Weakness or fatigue
  • A lump in your belly or rectum

Your doctor may give you a physical exam and feel your belly for any swollen organs or masses. They might also order one or more of these tests to spot polyps or colorectal cancer:

  • Rectal exam. Your doctor can use their fingers to feel for growths.
  • Colonoscopy. This is the standard screening test that experts recommend. Your doctor uses a thin, flexible tube called a colonoscope to look at your entire colon and rectum.
  • Sigmoidoscopy. Your doctor looks at your rectum and the last part of your colon.
  • Biopsy. Your doctor may take out a bit of tissue during a colonoscopy or sigmoidoscopy and send it to a lab for testing. They can also use a needle to take a sample, with a CT scan or ultrasound to guide them. Complications are rare, but you may have some bleeding or discomfort.
  • Stool DNA. This test looks for certain gene changes that might be a sign of colon cancer.
  • CT colonography. This is a special X-ray (also called a virtual colonoscopy) of your entire colon. It takes less time and is less invasive than other tests. But if it shows a polyp, you’ll still need a colonoscopy.
  • Barium enema X-ray. This is a type of X-ray that involves putting dye in your colon. It can find trouble spots that might mean you need a colonoscopy.
  • Other imaging tests. MRI or ultrasound can give your doctor a better look at your organs.

Tumors may bleed in amounts so small that only special tests can find it. This is called occult bleeding, meaning you probably can’t see it with the naked eye. These tests can look for blood in your poop:

  • Fecal immunochemical test (FIT). This reacts to part of human hemoglobin, a protein in red blood cells. You can do the test at home and mail a sample of poop to a lab.
  • Guaiac-based fecal occult blood tests (gFOBT). This uses a chemical to look for blood. You can do it at home and mail in a card with a sample of poop on it.

If either of these tests finds blood, your doctor will probably recommend a colonoscopy.

If a test finds a polyp, your doctor will take it out and send it to a laboratory. A specialist will look at it under a microscope. Your doctor will discuss the results with you. They will recommend next steps, including when to have another colonoscopy.

If you have colorectal cancer, tests can tell your doctor whether it has grown or spread. This process is called staging. The stages of colorectal cancer are:

  • Stage 0. The cancer hasn’t gone past the inner layer of your colon or rectum. This is also called cancer in situ.
  • Stage I. The cancer has grown into the muscles of your colon or rectum.
  • Stage IIA. It’s spread through the colon or rectum wall.
  • Stage IIB. It’s grown into the lining of your abdomen (peritoneum).
  • Stage IIC. The cancer has spread through your colon or rectum wall and into nearby tissues.
  • Stage IIIA. It’s spread to three or fewer lymph nodes or to tissues around your colon or rectum.
  • Stage IIIB. It’s grown through the wall of your bowel or into nearby organs. It’s also spread to three or fewer lymph nodes or to tissues around your colon or rectum.
  • Stage IIIC. The cancer has spread to four or more lymph nodes.
  • Stage IVA. Cancer has spread to one part of your body that’s farther away, like your liver or lungs.
  • Stage IVB. It’s spread to more than one part of your body.
  • Stage IVC. Cancer has grown in the lining of your abdomen and possibly to lymph nodes or organs that are farther away.

Treatment will depend on several things. You and your doctor should consider:

  • The stage of the disease
  • How well certain treatments will work for you
  • Your overall health
  • The risks and side effects
  • How much the treatment costs
  • The option you’d prefer

You might have one or more of these treatments:


Your doctor can take out polyps and small tumors that haven’t spread during a colonoscopy or through a laparoscopy, in which they put special tools and cameras into your belly through small cuts. If the cancer has spread, you might have surgery to remove part of your colon (partial colectomy).

If cancer has spread to your liver and nowhere else, surgery is your best chance for a cure. But it’s not an option for everyone. Your doctor must be able to take out all the cancer. And you need enough healthy tissue left over for your liver to still work. If your tumor is very large, you might have chemotherapy to help shrink it before surgery.

Procedures called ablation and embolization can also treat cancer that has spread to the liver. They can destroy tumors without removing them. Sometimes, doctors use high-energy radio waves or electromagnetic microwaves to kill cancer cells. Or they may inject the tumor with alcohol or freeze it with a metal probe. With embolization, a substance blocks blood flow to the tumor.

Radiation therapy

Radiation therapy uses high-energy X-rays, electron beams, or chemical agents called radioactive isotopes to attack cancer. The radiation is aimed directly at the tumor. It damages chromosomes in cancer cells so they can't multiply.

External radiation therapy is the most common form for people with colorectal cancer. A machine aims a beam of radiation at your tumor. It's painless.

Before treatment begins, a team of specialists, including a radiation oncologist, will use measurements from scans to find the exact spot to aim the radiation. They'll tattoo small dots on your body to show where to target the beam. This ensures that they get the same location at every treatment.

You'll need to be still during the procedure, but it lasts only a few minutes. You may have five treatments a week for several weeks, and sometimes, you'll be treated a few times a day for several weeks.

There are many kinds of external beam radiation. These include 2D, 3D conformal, IMRT, IGRT, and proton beam therapy.

Radiation can also be internal. Interstitial radiation therapy (also known as brachytherapy) uses a tube to place small pellets, or seeds, of radioactive material directly into your tumor. After 15 minutes, they're taken out. You may have up to two treatments a week for 2 weeks.

Endocavitary radiation therapy is often used for rectal cancer. A device called a proctoscope is placed in your anus to carry radiation directly to the tumor. It stays there a few minutes and then is taken out. You'll probably have four treatments, each about 2 weeks apart.

Side effects tend to be specific to the area of your body that gets the radiation. Talk to your doctor about what you can expect.

You may have:

  • Blood in your stool
  • Lack of energy
  • Leaky bowels
  • Pain and burning on your skin where beams were aimed
  • Pain during bowel movements
  • Pain when you pee
  • Problems having sex

Most side effects should get better a few weeks after treatment ends, but some may not go away. Medications and other treatments may help.

Radiofrequency ablation

This kills cancer cells using a probe with electrodes.


Chemo drugs destroy cancer cells or stop them from spreading. You can take the medicines in pill form or through an IV. You can also get them in a blood vessel close to your tumor. There are many types of these drugs. Some work better together, so you may take two or more at the same time. You usually get the treatment for 2 or 4 weeks and then take a break.

You might have chemo after surgery to kill any cancer cells left behind. Or you could have it before an operation to make a tumor smaller and easier to remove. Chemo may help treat cancer pain too. And it's often the best way to slow the spread of the disease.

The downside is that the drugs can attack healthy cells as well as cancerous ones. This can cause side effects like hair loss, vomiting, and mouth sores. You may also feel very tired and get sick easily. But these problems usually get better when your treatment is over.


Immunotherapy, a type of biological therapy, uses your body's immune system to fight cancer. It includes:

  • Biological response modifiers. These trigger the immune system to indirectly affect tumors. Biological response modifiers include cytokines (chemicals produced by cells to instruct other cells) such as interferons and interleukins. This strategy involves giving larger amounts of these substances by injection or infusion in the hope of stimulating the cells of the immune system to act more effectively.
  • Colony-stimulating factors. These things signal your body to make bone marrow cells (the soft, sponge-like material inside bones), which include both red and white blood cells and platelets. White blood cells fight infection; red blood cells carry oxygen to and carbon dioxide from organs and tissues; platelets are cell fragments that help the blood clot. Often, other cancer treatments cause decreases in these cells. Thus, colony-stimulating factors don’t directly affect tumors, but they can help support your immune system during cancer treatment.
  • Monoclonal antibodies. These lab-made things find and bind to cancer cells wherever they are in the body. They can be used to see where the tumor is in the body (detection of cancer) and call in other immune system cells to destroy them, or as therapy to deliver drugs, toxins, or radioactive material directly to a tumor. Monoclonal antibodies for colorectal cancer include bevacizumab (Avastin), cetuximab (Erbitux), panitumumab (Vectibix), and ramucirumab (Cyramza).
  • Immune checkpoint inhibitors. These are drugs that take the “brakes” off of checkpoint proteins in the immune system, which helps these proteins recognize and attack cancer cells. They include ipilimumab (Yervoy), pembrolizumab, (Keytruda), and nivolumab (Opdivo).
  • Tumor vaccines. Researchers are developing vaccines that may encourage the immune system to better recognize cancer cells. In theory, they would work in a similar way as vaccines for measles, mumps, and other infections. The difference in cancer treatment is that vaccines are used after someone has cancer, rather than to prevent the disease. There are also ongoing studies involving possible vaccines to prevent breast and prostate cancers.

Like other forms of cancer treatment, immunotherapy may have a number of side effects. They can vary widely from person to person. Biologic response modifiers may cause flu-like symptoms, including fever, chills, nausea, and loss of appetite. In addition, rashes or swelling may develop at the injection site, and blood pressure may fall. Fatigue is another common side effect.

Colony-stimulating factors might cause bone pain, fatigue, fever, and loss of appetite.

The side effects of monoclonal antibodies vary. They may include serious allergic reactions. Rashes are common and may be a severe side effect of Erbitux or Vectibix. They usually mean that these drugs are working.

Bleeding, blood clotting, or bowel perforation may be side effects of Avastin or Cyramza.

Vaccines can cause muscle aches and low-grade fever.

Immune checkpoint inhibitors can have serious side effects. One concern is that they can allow the immune system to attack normal organs in the body. More common side effects include fatigue, cough, loss of appetite, and rash.

Targeted therapy

This uses drugs that focus on specific things in cancer cells, like genes or proteins, to kill them or keep them from growing.

Some come in pill form. You get others in your vein (IV) at a hospital, doctor’s office, or clinic. Most are given along with standard chemo medicines.

Medications used as targeted therapies for colorectal cancer include:

Targeted therapies can cause serious side effects. Some of the most common are:

  • Diarrhea
  • Blood clots
  • Bleeding in the GI tract
  • Allergic reactions
  • Liver diseases like hepatitis and skin rash or peeling

Palliative (supportive) care

This doesn’t try to cure cancer. Its goal is to help you feel better. It also provides support for your family and caregivers. And it can help you make decisions about the kind of care you want in the months and years ahead.

Ask your doctor about palliative care as soon as you find out that you have cancer. Your care team can prescribe meds to ease pain and side effects. Palliative care can also ease depression and may help you live longer.

After you’ve finished your treatments for colorectal cancer, follow-up care is very important. Regular checkups can help find any changes in your health, and if the cancer comes back (or “recurs”), it can be treated as soon as possible.

Ongoing care

You may need to see many different doctors during the months and years after you finish treatment. Your oncologist will usually start out as your main contact. They’ll give you a schedule for screenings and tests.

They may ask your primary care doctor to take over your care at some point. Be sure you have a summary of your cancer treatment that includes:

  • Your follow-up plan from your oncologist
  • Names and doses of all your chemotherapy drugs or other medicines
  • The dates and specifics of your diagnosis (including cancer stage and other details)
  • Any side effects or complications of treatment
  • Types and dates of all surgeries and locations where they were done
  • Dates and amounts of radiation and where it was done
  • Contact info for all of your doctors

Bring this summary with you for all your appointments, since you may not always see the same doctor.

Ask your doctor any questions you may have about your day-to-day life, such as whether it would help to make changes in your diet or exercise habits.

Tell them about any supplements you take, even “natural” products or vitamins and minerals. That way, your doctor can check on anything that might have side effects or interact with your medicines.

If you feel down or anxious, tell your doctor that, too. They may be able to recommend a counselor or a support group.

Follow-up tests

What types of screenings you have and how often you get them will depend on the type and stage of cancer you had and the treatments you got. You'll probably need check-ups three to four times a year during the first 2 or 3 years after treatment and one or two times a year after that. These might include:

  • A physical exam
  • Colonoscopy, usually 6 months to 1 year after surgery. Your doctor can tell you how often you'll need one.
  • CT scans of your chest, abdomen, and possibly pelvis every 6 to 12 months for the first 3 years
  • CEA (carcinoembryonic antigen) blood test every 3 to 6 months for 5 years. High levels of CEA protein in the blood may mean cancer cells have spread.

When to call your doctor

Call your doctor right away if you have:

A healthy tobacco-free lifestyle is the first step in preventing cancer of any kind.

Experts recommend that as an initial step toward the prevention of colorectal cancer, people should exercise and eat healthily. The American Cancer Society says adults should get 150 minutes of moderate-intensity or 75 minutes of high-intensity exercise (or a combination of these) each week.

The National Cancer Institute recommends a low-fat, high-fiber diet that includes at least 2 1/2 cups of fruits and vegetables each day. Cut back on red meat and other high-fat foods, such as eggs and many dairy products. You can get the protein you need from low-fat dairy products (also a good source of calcium), nuts, beans, lentils, and soybean products. Avoid overcooking or barbecuing meats and fish.

Some experts suggest that aspirin may stop colorectal cancer cells from multiplying. In addition, other non-steroidal anti-inflammatory drugs (NSAIDs, such as Aleve and Motrin) may reduce the size of polyps and, therefore, the risk of colon cancer. This theory has not been well established, and the proper dosage is unclear. Also, NSAIDs may raise your odds of serious complications, such as stomach bleeding, heart attacks, and strokes. If you’re at high risk of colon cancer, don’t start taking aspirin or other NSAIDs until you discuss it with your doctor.

Women who have gone through menopause and who take hormone replacement therapy that includes both estrogen and progesterone may be less likely to get colon cancer. But if they do, it may be more advanced when it’s found. Hormone replacement therapy also raises the risk of other cancers. Talk with your doctor about the risks and benefits.

Screening for colorectal cancer is crucial. The American Cancer Society and the US Preventive Services Task Force recommends that people get regular screening exams from ages 45 to 75 if they have an average chance of getting colorectal cancer. This means that you don’t have symptoms and that neither you nor a close family member has had colorectal polyps, cancer, or inflammatory bowel disease.

The guidelines include at least one of these tests:

  • Tests for blood in your poop once a year
  • Stool DNA tests every 3 years
  • Flexible sigmoidoscopy every 5 years
  • CT colonography (virtual colonoscopy) every 5 years
  • Colonoscopy every 10 years

Talk to your doctor if you have one or more of the colorectal cancer risk factors. You might need to start screenings at a younger age, get tested more often, or have specific kinds of tests.

If you’re 76 through 85, talk to your doctor about whether you should be tested. The American Cancer Society doesn’t recommend testing for people older than 85.