Colorectal Cancer

Written by Sarah Gleim
Medically Reviewed by Shruthi N, MD on March 23, 2025

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

"You're more at risk for colorectal cancer if you have a close family member with a history of the disease, have inflammatory bowel disease, and as part of aging. Eating red and processed meats increases your risk as well," says William Jonas, MD, an oncologist with Piedmont Cancer Institute. "Ask family members with a history of colorectal cancer if they were evaluated for genetically linked causes for their colorectal cancer. If so, discuss with your doctor what steps can be taken to reduce your risks."

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 steps to prevent colorectal cancer. If you find it when it's small and hasn't spread, it may be easier for your doctors to treat. 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 90%-95% of cases. It starts in cells that make mucus for your colon and rectum.

Carcinoid tumors. These are tumors that form in hormone-producing cells of the large intestine.

Gastrointestinal stromal tumors. These also form in the large intestine. They start out as benign tumors in the gastrointestinal muscles and then turn into cancer. 

Lymphoma. This colon cancer is part of your immune system structure.

Familial adenomatous polyposis(FAP). This type of hereditary colon cancer causes hundreds of polyps to develop in the colon and rectum that eventually turn cancerous.

Hereditary nonpolyposis colorectal cancer (HNPCC). Another type of hereditary colon cancer, HNPCC is also called Lynch syndrome.

Several genetic mutations can also lead to colorectal cancer, including:

  • Juvenile polyposis coli
  • Peutz-Jeghers syndrome (PJS)
  • Turcot syndrome

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 are usually benign and don't have a risk of turning into 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. Large adenomas are considered precancerous and are always removed during a colonoscopy.

Colorectal cancer risk factors

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 24 for men and 1 in 26 for women.

Other things that can raise your chances of getting colorectal cancer include:

Inflammatory bowel disease, such as Crohn's disease or ulcerative colitis

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 polyps
  • 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, such as constipation or diarrhea
  • A feeling that your bowel hasn’t emptied fully 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
  • 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 suggest. 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 them. 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.

Colorectal polyps

If a test finds a polyp, your doctor will take it out and send it to a lab. 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 but not to nearby lymph nodes.

Stage IIA. The cancer has grown into the outermost layers of the colon or rectum but not through them.

Stage IIB. It's grown through the wall of the colon or rectum but not into nearby tissues or lymph nodes.

Stage IIC. The cancer has spread through your colon or rectum wall into nearby tissues but not into nearby lymph nodes.

Stage IIIA. It's spread to three or fewer lymph nodes or to tissues around your colon or rectum.

Stage IIIB. It’s grown into the outermost layers of the colon or rectum but not into nearby organs.

Stage IIIC. The cancer has grown through the wall of the colon or rectum and is attached to nearby tissues or organs. Or it hasn't reached nearby organs but has spread to at least seven nearby lymph nodes.

Stage IVA. The cancer has spread to one distant organ, like your liver or lungs, or a set of lymph nodes.

Stage IVB. The cancer has spread to more than one distant organ or set of lymph nodes.

Stage IVC. The cancer has grown in the lining of your abdomen and possibly to distant lymph nodes or organs.

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:

Surgery

Your doctor can take out polyps and small tumors during a colonoscopy or through a laparoscopy as long as they haven't spread. 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 treatment option, but it's not for everyone. Your doctor must be able to remove 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 need chemotherapy to help shrink it before surgery.

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 your tumor and damages chromosomes in cancer cells so they can't multiply.

External radiation therapy

This is the most common type to treat 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, uses measurements from scans to find the exact spot to aim the radiation. They 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.

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 two weeks.

Endocavitary radiation therapy.

It 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 for a few minutes and then is taken out. You'll probably have four treatments, each about two 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.

Ablation and embolization

These procedures are often used to treat colorectal cancer when small tumors spread to other organs in your body, such as your liver or lungs. 

  • Radiofrequency ablation uses high-energy radio waves to kill smaller tumors that may have spread to other parts of your body, especially the liver.
  • Microwave ablation uses high temperatures to kill tumors in the liver using a needle-like probe. It's mainly used on tumors larger than 6 centimeters across.
  • Percutaneous ethanol ablation (PEI) kills cancer cells with concentrated alcohol injections.
  • Cryoablation uses liquid nitrogen to freeze tumors and kill cancer cells. 
  • Arterial embolization places particles into your liver's hepatic artery to block the cancer from receiving oxygen and nutrients.
  • Chemoembolization combines arterial embolization with chemo by giving you chemo through a catheter directly into the artery feeding the tumor and plugging it so the medication stays there.
  • Radioembolization combines embolization and radiation therapy by injecting radioactive-coated beads (microspheres) into your hepatic artery where they radiate the tumor for several days.

Chemotherapy

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 two or four 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 your 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

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 approach 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).

Like other forms of cancer treatment, immunotherapy may have several 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 some monoclonal antibody treatments.
  • Immune checkpoint inhibitors can have serious side effects, including allowing your immune system to attack your organs. Other side effects include fatigue, cough, loss of appetite, and rash.

Targeted therapy

This uses drugs that focus on specific things in cancer cells, such as 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:

  • Aflibercept (Zaltrap)
  • Bevacizumab (Avastin)
  • Cetuximab (Erbitux)
  • Panitumumab (Vectibix)
  • Ramucirumab (Cyramza)

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

  • Diarrhea
  • Blood clots
  • Bleeding in the gastrointestinal tract
  • Allergic reactions
  • Liver diseases, such as hepatitis and skin rash or peeling

Palliative (supportive) care

The goal of palliative care isn't to treat your cancer; it's simply to treat your symptoms and help you feel better. It also offers 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, 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 be your main contact, but they may ask your regular doctor to take over your care. 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

Take this summary with you for all your appointments, as 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 suggest a counselor or a support group.

Follow-up tests

The 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 checkups three to four times a year for the first two or three years after treatment and one or two times a year after that. These might include:

  • A physical exam
  • Colonoscopy, usually 6-12 months after surgery ( Your doctor can tell you how often you'll need one.
  • CT scans of your chest, abdomen, and possibly pelvis every 6-12 months for the first three years
  • Carcinoembryonic antigen (CEA) blood test every three to six months for five 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:

  • Belly pain, weight loss, or blood in your stool
  • Fatigue that gets in the way of your daily life
  • Problems with your bowel movements, bladder, or sexual function
  • Mental changes, such as trouble concentrating, anxiety, depression, or memory loss
  • Trouble sleeping
  • Changes in your family medical history, such as relatives who've recently been diagnosed with cancer

"You can lower your risks of colorectal cancer by eating a diet high in fruits and vegetables, getting more exercise, and drinking less alcohol," Jonas says. "And if you smoke, stop."

The National Cancer Institute recommends a low-fat, high-fiber diet that includes at least two and a half 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.

A 2024 Harvard study found that aspirin may lower the risk of colorectal cancer in people who are at high risk. The study followed more than 100,000 men and women for 30 years and discovered that aspirin may also block signal pathways that cause cancer cells to grow out of control. The study didn't include side effects of daily aspirin use, so don't start taking aspirin 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 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 three years
  • Flexible sigmoidoscopy every five years
  • CT colonography (virtual colonoscopy) every five 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 suggest testing for people older than 85.

Colorectal cancer is the third leading cause of cancer deaths among American men and women. It starts when cells that line your colon or rectum grow out of control. You may not notice any symptoms, but if you find it early and it hasn't spread, it may be easier for your doctors to treat. It's important to have regular screenings and exams to spot polyps and precancerous areas, especially if you have a high risk of getting colorectal cancer.

Is colorectal cancer the same as colon cancer?

Cancer that begins in the colon is called colon cancer, while cancer that begins in the rectum is called rectal cancer. Cancer that affects either of these parts may also be called colorectal cancer. They're similar, but not exactly the same.

What is the life expectancy of someone with colorectal cancer?

Life expectancy depends on many different things, including your cancer stage at diagnosis. But according to the American Cancer Society, 60% of Black people, 65% of White people, and 67% of Asian American and Pacific Islanders were still alive five years after being diagnosed with colorectal cancer. 

How common is colorectal cancer?

Colorectal cancer is the third most common cancer in the world. Nearly 10% of all cancer cases are colorectal, and it's the second leading cause of cancer-related deaths worldwide.

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