Colon cancer

This disease is also called colorectal or rectal cancer, depending where it starts. Most start as a growth—called a polyp—on the inner lining of the colon or rectum.

Meet Priscilla

Lady holding a blowtorch

It can be easy to dismiss digestive symptoms as nothing, especially when there are so many fad diets that promise to eliminate bloating and belly discomfort. Priscilla Gonzalez knows this all too well. In 2019, she began feeling bloated and uncomfortable constantly. Like many, she shrugged it off as a dairy issue and changed her diet. When the bloat didn’t disappear, she tried home remedies.

“I thought it would just resolve,” Gonzalez said. She didn’t have time for anything else. Then, she started seeing blood in her stool. A month went by before Priscilla’s husband finally convinced her to go to a clinic and get her blood drawn. The clinic called Priscilla before she got home, saying she needed to go to the ER right away. Her blood count was extremely low, and she may need a transfusion.

The cause? Colon cancer.

What is Colon Cancer?

Colon cancer is also called colorectal cancer or rectal cancer, depending on where it starts. It is a type of cancer that affects the large intestine (colon) and rectum. The large intestine is the last part of the digestive tract. The colon is responsible for reclaiming water from the food we eat and forming waste (stool) to pass from the body. The rectum is connected to the anus. It functions to store stool and signals that you need to have a bowel movement.

The walls of the colon and rectum are made up of many layers. Colon cancer usually starts as a small growth – called a polyp – on the innermost layer of the colon or rectum. As it grows, colorectal cancer may invade the wall’s other layers. The cancer can then invade blood vessels or lymph vessels, tiny channels that carry away waste and fluid. Once in the blood vessels or lymph nodes, cancer cells may move to other parts of the body. This is how colon cancer spreads (metastasis).

Not all polyps found in the colon become cancer, but we do know that some types of polyps can change into cancer over several years. The chance of this happening depends on the type of polyp.

There are two main polyp types:

  • Adenomatous polyps or adenomas. These polyps sometimes change into cancer, so adenomas are considered a precancerous condition.
  • Hyperplastic polyps and inflammatory polyps. These polyps are more common, but in general, they are not precancerous.

Other factors that can make a polyp more likely to contain cancer or develop into colorectal cancer include:

  • The polyp is larger than one centimeter.
  • More than two polyps are found.
  • Dysplasia. Dysplasia describes an area within a polyp or the lining of the large intestine where the cells look abnormal but don’t look like true cancer cells. Dysplasia is a precancerous condition.

Types of colon and rectal cancer

  • Adenocarcinomas. The vast majority of colorectal cancers – about 96% of cases – are adenocarcinomas. These cancers start in cells that make mucus to lubricate the inside of the colon and rectum.
  • Carcinoid tumors. These tumors start from special hormone-making cells in the intestine.
  • Gastrointestinal stromal tumors (GISTs). These tumors start from special cells in the wall of the colon called the interstitial cells of Cajal.
  • Lymphomas. These are cancers of immune system cells that mostly start in lymph nodes, but they can also start in the colon, rectum or other organs.
  • Sarcomas. These tumors can start in blood vessels, muscle layers or other connective tissues in the wall of the colon and rectum. Sarcomas of the colon or rectum are rare.

What are the risk factors for colon cancer?

One reason Priscilla Gonzalez didn’t act on her symptoms right away was that she thought her risks of colorectal cancer were low. She was a healthy, active mother of two. She was only 39, and most colon cancer cases occur after age 50. Priscilla’s paternal grandmother’s sister died of colon cancer, but she wasn’t a first-degree relative (like a sibling, parent or child) so Priscilla didn’t think much of it. What Priscilla didn’t know was that a family history of breast, ovarian or uterine cancer also increases your risk of developing colorectal cancer. Additionally, if a male relative was diagnosed with breast cancer, your risk for developing colorectal cancer increases. Priscilla’s grandmother and mother were both uterine cancer survivors, meaning that she was, in fact, at risk for colorectal cancer.

Other risk factors for colorectal cancer include:

  • Aging. Younger adults can get colorectal cancer, but it’s much more common after age 50.
  • A personal history of colorectal polyps or colorectal cancer. If you have a history of adenomas, you are at increased risk of developing colorectal cancer. This is especially true if the polyps are large, if there are many of them, or if any of them show dysplasia. If you’ve had colorectal cancer, even though it was completely removed, you are more likely to develop new cancers in other parts of the colon and rectum. The chances of this happening are greater if you had your first colorectal cancer when you were younger.
  • A personal history of inflammatory bowel disease (IBD) . This includes either ulcerative colitis or Crohn’s disease. IBD is different from irritable bowel syndrome (IBS), which does not increase your risk for colorectal cancer.
  • A family history of colorectal cancer or adenomas. Most colorectal cancers are found in people without a family history of it, but nearly one in three people who develop it have other family members who have had it. If you have a family history of adenomatous polyps or colorectal cancer, talk with your doctor about the possible need to start screening before age 45.
  • Having an inherited syndrome.
  • Your racial and ethnic background. African Americans have the highest colorectal cancer incidence and mortality rates of all racial groups in the U.S. The reasons for this are not fully understood. Jews of eastern European descent (Ashkenazi Jews) have one of the highest colorectal cancer risks of any ethnic group in the world.
  • Having type 2 diabetes. People with type 2 (usually non-insulin dependent) diabetes have an increased risk of colorectal cancer.

Some risk factors for colorectal cancer are related to your lifestyle. In fact, the links between diet, weight, and exercise and colorectal cancer risk are some of the strongest for any type of cancer.

Acquired risk factors for colorectal cancer include:

  • Being overweight or obese. This raises the risk of colon and rectal cancer in both men and women, but the link seems to be stronger in men.
  • Physical inactivity.
  • Certain types of diets. A diet that’s high in red meats and processed meats raises your colorectal cancer risk.
  • Smoking.
  • Heavy alcohol use. Limiting alcohol use to no more than 2 drinks a day for men and 1 drink a day for women could have many health benefits, including a lower risk of many kinds of cancer.

What causes colorectal cancer?

In general, cancer is caused by mutations in the DNA inside our cells, but we don’t fully understand what causes these mutations or how they lead to cancer. However, we do know of some genetic mutations that can increase your chance of getting colorectal cancer.

Inherited mutations. Some mutations to our DNA can be passed on to the next generation. People who are born with an inherited mutation have that mutation in all of their cells.  These are called inherited mutations, and a very small number of colorectal cancers are caused by inherited gene mutations, including:

  • Familial adenomatous polyposis (FAP), attenuated FAP (AFAP), and Gardner syndrome. Causes hundreds of polyps to form in the colon. Over time, cancer will nearly always develop in one or more of these polyps.
  • Lynch syndrome (hereditary non-polyposis colon cancer, or HNPCC).
  • Peutz-Jeghers syndrome.
  • MYH-associated polyposis (MAP).

Acquired mutations. Most gene mutations that lead to cancer are acquired mutations that affect only a few cells. Acquired mutations happen during a person’s lifetime due to environmental or other factors. Most cases of colorectal cancer are due to acquired mutations rather than inherited mutations. In many cases, the first mutation occurs in the APC gene. This gene is involved in “putting the brakes” on cell growth. If it doesn’t function properly, cells may grow out of control, leading to cancer.

Certain risk factors probably play a role in causing these acquired mutations, but so far it’s not known what causes most of them.

Colorectal Cancer Symptoms

Bloating and discomfort are often initial symptoms. However, because these symptoms are shared by a variety of other gastrointestinal diseases, be sure to see your UCHealth providers if you have any of the following:

  • A change in bowel habits, such as diarrhea, constipation or narrowing of the stool that lasts for more than a few days.
  • A feeling that you need to have a bowel movement that’s not relieved by having one.
  • Blood in the stool, which may make the stool look dark.
  • Cramping or abdominal (belly) pain.
  • Rectal bleeding with bright red blood.
  • Unintended weight loss.
  • Weakness and fatigue.

Early colon cancer may not present with any signs or symptoms, and because it typically grows slowly, symptoms may not present for years.

Sometimes, the first sign of colorectal cancer is a blood test that shows a low red blood cell count. This is why getting regular check ups and colon cancer screenings as you age is so important. The American Cancer Society recommends adults get a colon cancer screening starting at age 45. If you, like Priscilla, have an increased risk of colon cancer, talk to your doctor about starting your screenings earlier.

Questions and answers about colon cancer (FAQs)

Can colon cancer occur and not cause any symptoms?

Yes, early colon cancer may not present with any signs or symptoms, and because it typically grows slowly, symptoms may not present for years.

Is there a link between eating red meat and colon cancer?

Yes, research has shown that eating red meat and processed meats increases your risk of getting colon cancer. In addition, obesity is a risk factor, especially when the weight gain occurs between early adulthood and middle age.

Is there an age range for colonoscopies?

The current guidelines suggest that colonoscopies should be performed from age 45 to 75. However, a provider may prescribe a colonoscopy for adult patients of any age.

Source: U.S. Preventive Services Task Force via

How Colon Cancer is Diagnosed

Properly diagnosing colon cancer and identifying the type are the first steps towards creating a cancer treatment plan. Your provider may use one or more of the following tests to determine whether you have colon cancer and if it has spread:

Medical history and physical exam. Your doctor will take your medical history and will ask about any symptoms, including when they started and how long you’ve had them. As part of a physical exam, your doctor will feel your abdomen for masses or enlarged organs, and also examine the rest of your body. You may also have a digital rectal exam (DRE). During this test, the doctor inserts a lubricated, gloved finger into your rectum to feel for any abnormal areas.

Tests to look for blood in your stool. Your doctor may recommend a test to check your stool for blood that isn’t visible to the naked eye, called occult blood. You would do this at home, either a fecal occult blood test (FOBT) or a fecal immunochemical test (FIT).

Blood tests. Your doctor might also order certain blood tests to be used to help monitor your disease if you’ve been diagnosed with cancer

  • Complete blood count (CBC). This test measures the different types of cells in your blood, and it can show if you have anemia.
  • Liver enzymes. You may also have a blood test to check your liver function because colorectal cancer can spread to the liver.
  • Tumor markers. Blood tests for these tumor markers can sometimes suggest someone has colorectal cancer, but they can’t be used alone to diagnose cancer.

Diagnostic colonoscopy. Your doctor looks at the entire length of your colon and rectum with a colonoscope, a thin, flexible, lighted tube with a small video camera on the end. Special instruments can be passed through the colonoscope to biopsy or remove any suspicious-looking areas such as polyps.

Proctoscope. This may be done if rectal cancer is suspected. Your doctor looks inside the rectum with a proctoscope, which is similar to a colonoscope but smaller. The tumor can be seen, measured, and its exact location can be determined.

Biopsy. This is the definitive step in a proper diagnosis. Your doctor removes a small piece of tissue with a special instrument passed through a scope. A pathologist examines the biopsy samples under a microscope, and if cancer is found, other lab tests may done to help better classify the cancer.

Imaging Tests

Imaging tests use sound waves, x-rays, magnetic fields or radioactive substances to create pictures of the inside of your body. Possible tests include:

  • Computed tomography (CT or CAT) scan. Helps us see if colon cancer has spread into your liver or other organs.
  • Abdominal ultrasound. Can be used to look for tumors in your liver, gallbladder, pancreas or elsewhere in your abdomen, but it can’t look for tumors of the colon.
  • Endorectal ultrasound. Used to see how far through the rectal wall a cancer has grown and whether it has reached nearby organs or tissues such as lymph nodes.
  • Intraoperative ultrasound. Done during surgery, allowing the surgeon to biopsy the tumor while the patient is asleep.
  • Magnetic resonance imaging (MRI) scan. Can be used to look at abnormal areas in the liver or the brain and spinal cord that could be cancer spread.
  • Endorectal MRI. MRI scans can be used in patients with rectal cancers to see if the tumor has spread into nearby structures.
  • Positron emission tomography (PET) scan. If you have already been diagnosed with cancer, your doctor may use this test to see if the cancer has spread to lymph nodes or other parts of the body. Some machines can do both a PET and CT scan at the same time.
  • Angiography. An x-ray test for looking at blood vessels.
  • Chest x-ray. May be done after colorectal cancer has been diagnosed to see if cancer has spread to the lungs.

Colon cancer staging

Staging is the process of determining how much cancer there is and whether it has spread. Doctors use staging to help guide treatment decisions. UCHealth follows the American Joint Committee on Cancer (AJCC) TNM system, the staging system most often used for colorectal cancer. It is based on three key pieces of information:

  1. The extent (size) of the tumor (T).
  2. The spread to nearby lymph nodes (N).
  3. The spread (metastasis) to distant sites (M).

The system described below is the most recent AJCC system, effective January 2018.

Cancer staging can be complex, so ask your doctor to explain it to you in a way you understand.

Colon Cancer stages

Colon cancer treatment and recovery

After being diagnosed with colon cancer, Priscilla Gonzalez found herself confronted with different treatment options. Her cancer was in the early stages, meaning surgery alone might be enough to cure it. But after talking things over with a UCHealth specialist, she decided she wanted to take chemotherapy after surgery to improve her odds of beating cancer. This is just one example of how important it is to talk with your care team; they will help you create the best treatment plan for your type of cancer.

Your cancer care plan may involve one or more of the following treatments:

Surgical treatments

Surgery is the most common treatment for all stages of colon cancer. Depending on the cancer stage, different types of surgery may be more appropriate for you.

  • Local excision (polypectomy). If the tumor is small and contained, your surgeon may be able to remove it during a colonoscopy.
  • Resection of the colon with anastomosis. Your surgeon removes part of the colon containing the cancer and nearby healthy tissue and then joins the cut ends of the colon.
  • Resection of the colon with colostomy. Your surgeon removes part of the colon containing the cancer and nearby healthy tissue. However, if the two ends of the colon cannot be joined together, your surgeon will construct another path for waste to leave your body. This is known as a colostomy. It involves attaching the end of the colon to a small opening in the wall of your abdomen. A bag fits securely over the opening and collects the waste.

Nonsurgical treatments

There are a variety of non-surgical treatments for colorectal cancer as well. These may be performed in place of surgery, or they may be performed before or after surgery to improve outcomes.

  • Radiofrequency ablation. A special probe with tiny electrodes that kill cancer cells.
  • Cryosurgery. An instrument that freezes and destroys abnormal tissue.
  • Chemotherapy. Drugs that destroy cancer cells, usually by stopping the cancer cells’ ability to grow and divide. At UCHealth, we often use more than one drug at a time for maximum results.
  • Targeted therapy or novel therapy. Drugs that target the cancer’s specific genes, proteins or the tissue environment that contributes to cancer growth and survival. In recent years, targeted therapy has proven to be increasingly successful at controlling certain cancers and improving cancer patients’ outlook.
  • Immunotherapy or biologic therapy. Uses materials made either by the body or in a laboratory to improve, target or restore immune system function.
  • Other drug therapy. We may give steroids alone or at the same time as targeted therapy or chemotherapy.
  • Radiation therapy. High-energy X-rays or other particles destroy cancer cells.

Regardless of your treatment, your body will need time to heal and recover. This may involve spending a few days in the hospital recuperating. You may also be encouraged to make some changes to your diet. Be sure to talk to your care team about this, so that you can feel better sooner.

Five-year colon and rectal cancer survival rates

UCHealth Cancer Survival Rates - Colon Cancer
UCHealth Cancer Survival Rates - Rectal Cancer

Data source: Surveillance, Epidemiology, and End Results (SEER) 17 registries, National Cancer Institute, 2022. AJCC All Stages, 5 Year Relative Survival. Date of diagnosis from 2012 – 2018.


Center for Disease Control and Prevention (CDC). What Is Colorectal Cancer? (

National Cancer Institute (NCI). Colorectal Cancer (

National Center for Biotechnology Information (NCBI): National Library of Medicine. Colon Cancer (

MedlinePlus: National Library of Medicine. Colorectal Cancer (