Colon cancer develops when tumorous growths form in the large intestine. It is now the third most common type of cancer in the United States.

The colon, or large intestine, is where the body draws out water and salt from solid waste. The waste then moves through the rectum and exits the body through the anus. Rectal cancer originates in the rectum, the final several inches of the large intestine, closest to the anus.

Colorectal cancer, which describes co-occurring colon cancer and rectal cancer, is common.

According to the American Cancer Society (ACS), colorectal cancer is the third most commonly diagnosed cancer in the U.S., aside from skin cancers. In 2021, the ACS predicts that 104,270 people in the U.S. will receive a new diagnosis of colon cancer.

Healthcare professionals recommend regular colorectal cancer screenings for adults aged 45–75.

In this article, we look at how to recognize and treat colon cancer, why it develops, and how to prevent it.

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Symptoms and signs may include one or more of the following:

Weight loss and abdominal pain usually occur in the later stages of the disease.

If cancer spreads to a new location in the body, such as the liver, it can cause additional symptoms, such as jaundice.

Early symptoms

Colon cancer often causes no symptoms in the earliest stages, but symptoms may become more noticeable as the disease progresses. If people do have symptoms in the early stages, they may include:

Symptoms in males

According to Brigham and Women’s Hospital, symptoms of colon cancer usually appear the same in males and females. Males may notice the symptoms listed above.

Learn more about colon cancer in males here.

Symptoms in females

Females may experience the same symptoms as listed above. In addition, if people who are menstruating have anemia from colon cancer, they may have irregular menstrual cycles.

There are different ways of assigning a stage to cancer. The stages indicate how far cancer has spread and the size of any tumors.

In colon cancer, the stages develop as follows:

  • Stage 0: Also known as carcinoma in situ, at this point, the cancer is in a very early stage. It has not grown farther than the inner layer of the colon and will usually be easy to treat.
  • Stage 1: Cancer has grown into the next layer of tissue.
  • Stage 2: Cancer has reached the outer layers of the colon but has not spread beyond the colon.
  • Stage 3: Cancer has grown through the outer layers of the colon and reached one to three lymph nodes. It has not spread to distant sites.
  • Stage 4: Cancer has reached other tissues beyond the wall of the colon. As stage 4 progresses, colon cancer reaches distant parts of the body.

Learn about the outlook for stage 4 colon cancer here.

Usually, cells follow an orderly process of growth, division, and death. Cancer can develop when cells grow and divide uncontrollably and do not die at the normal point in their life cycle.

According to the ACS, researchers are unsure of the exact cause of colon cancer, but certain factors may increase the risk.

Cancer happens as a result of changes in DNA within cells. Certain genes called oncogenes help cells stay alive, grow, and divide. Tumor suppressor genes help regulate cell division and cell death.

Changes to DNA can affect oncogenes and tumor suppressor genes, resulting in multiple gene changes that may lead to colon cancer.

Polyps are growths that form on the inside of the colon. Polyps are noncancerous, but cancer can begin with some types of polyps.

If a person has a type of noncancerous polyp called an adenomatous polyp, they have an increased risk of developing colon cancer. These polyps form on the inner walls of the large intestine.

Cancerous cells may spread from malignant tumors to other parts of the body through the blood and lymph systems.

These cancer cells can grow and invade healthy tissue nearby and throughout the body in a process called metastasis. The result is a more serious, less treatable condition.

The exact causes of colon cancer are unknown, but there are several potential risk factors.

Polyps

Colon cancer can develop from precancerous polyps that grow in the large intestine. Some of these polyps may grow into malignant colon cancer if a surgeon does not remove them during the early stages of treatment. Types of polyps include:

Adenomas

Adenomas may resemble the lining of a healthy colon but appear different under a microscope. They can become cancerous.

Hyperplastic polyps

Colon cancer rarely develops from hyperplastic polyps, as they are typically benign.

Learn more about colon polyps here.

Genes

Uncontrolled cell growth can occur following genetic damage or changes to DNA.

Most genetic mutations occur during a person’s lifetime, rather than a mutation they inherited from a family member.

Around 5–10% of colon cancers result from specific hereditary conditions that increase the risk of polyps, colon cancer, and potentially other cancers in some members of the family.

Several inherited conditions also increase the risk of colon cancer, including:

  • attenuated familial adenomatous polyposis
  • familial adenomatous polyposis (FAP)
  • Gardner syndrome, which is a different type of FAP
  • Lynch syndrome, or hereditary nonpolyposis colorectal cancer
  • juvenile polyposis syndrome
  • Muir–Torre syndrome, which is a variant of Lynch syndrome
  • MUTYH-associated polyposis
  • Peutz–Jeghers syndrome
  • Turcot syndrome, another variant of FAP

It is possible to have these genetic features without developing cancer.

Traits, habits, and diet

Age is a significant risk factor for colon cancer. Around 90% of people who receive a diagnosis of colorectal cancer are over 50 years of age. However, it is becoming more common in people under 50.

Colon cancer is more likely to affect people with inactive lifestyles, those with obesity, and individuals who use tobacco.

As the colon is part of the digestive system, diet and nutrition play central roles in its development.

Low fiber diets can contribute. Also, according to one 2019 review, people who consume excessive amounts of the following have an increased risk:

Underlying conditions

Some conditions and treatments have links to an increased risk of colon cancer. These include:

Other risk factors

Other risk factors for colon cancer include:

  • having a parent, sibling, or child with a history of colon or rectal cancer
  • a personal history of colon, rectal, or ovarian cancer
  • a personal history of polyps 1 centimeter or more in size, or with abnormal cells
  • inherited genetic conditions, such as Lynch syndrome
  • having chronic ulcerative colitis or Crohn’s disease for 8 years or longer
  • regularly consuming alcohol three or more times a day
  • smoking cigarettes
  • older age
  • lack of physical activity
  • low fiber, high fat diets lacking in fruit and vegetables
  • race and ethnicity, as African Americans, Asians, and people of Hispanic descent may receive a colon cancer diagnosis at a later stage of the disease

Learn more about racial disparities in cancer diagnosis and treatment here.

Treatment will depend on the type and stage of colon cancer. A doctor will also consider a person’s age, overall health, and certain other characteristics when deciding on the best treatment option.

There is no single treatment for colon cancer, and options may include surgery, chemotherapy, and radiation therapy.

The aim of treatment will be to remove the cancer, prevent its spread, and reduce any uncomfortable symptoms.

Surgery

The main treatment for early stage colon cancer is usually surgery. If the cancer is only present in a polyp, people may just require a polypectomy to remove the cancerous polyp.

Surgery to remove part or all of the colon is a colectomy. During this procedure, a surgeon will remove the part of the colon that contains cancer, as well as some of the surrounding area.

A surgeon may remove nearby lymph nodes to reduce the risk of spreading. The surgeon will then either reattach the healthy portion of the colon or create a stoma, depending on the extent of the colectomy.

A stoma is a surgical opening in the wall of the abdomen. Through this opening, waste passes into a bag, which removes the need for the lower part of the colon. This is a colostomy.

Other types of surgery include:

  • Endoscopy: A surgeon may be able to remove some small, localized cancers using this procedure. They will insert a thin, flexible tube with a light and camera attached. It will also have an attachment for removing cancerous tissue.
  • Laparoscopic surgery: A surgeon will make several small incisions in the abdomen. This may be an option to remove larger polyps.
  • Palliative surgery: The aim of this type of surgery is to relieve symptoms in cases of untreatable or advanced cancers. A surgeon will attempt to relieve any blockage of the colon and manage pain, bleeding, and other symptoms.

Chemotherapy

During chemotherapy, a cancer care team will administer medications that interfere with the cell division process. They achieve this by disrupting proteins or DNA to damage and kill cancer cells.

These treatments target any rapidly dividing cells, including healthy ones. These can usually recover from any chemotherapy-induced damage, but cancer cells cannot. The medicines travel through the whole body, and the treatment will take place in cycles, so the body has time to heal between doses.

A cancer specialist, or oncologist, may recommend chemotherapy to treat colon cancer:

  • before surgery to shrink a tumor to make it easier to remove
  • after surgery to kill any remaining cancer cells
  • if cancer has spread to other organs

Side effects of chemotherapy may include:

Combination therapies often use multiple types of chemotherapy or combine chemotherapy with other treatments.

Learn more about chemotherapy for colon cancer here.

Radiation therapy

Radiation therapy kills cancer cells by focusing high energy gamma rays on them. A cancer care team may use external radiation therapy, which expels these rays from a machine outside of the body.

With internal radiation, a doctor will implant radioactive materials near the cancer site in the form of a seed.

Some metals, such as radium, emit gamma rays. The radiation may also come from high energy X-rays. A doctor may request radiation therapy as a standalone treatment to shrink a tumor or destroy cancer cells. It can also be effective alongside other cancer treatments.

For colon cancer, cancer care teams tend not to administer radiation treatments until the later stages. They may use them if early stage rectal cancer has penetrated the wall of the rectum or traveled to nearby lymph nodes.

Side effects of radiation treatment may include:

  • mild skin changes that resemble sunburn or suntan
  • nausea
  • vomiting
  • diarrhea
  • fatigue
  • appetite loss
  • weight loss

Most side effects will resolve or subside a few weeks after completing treatment.

A physician will carry out a complete physical examination and ask about personal and family medical histories.

They may also use the following diagnostic techniques to identify and stage cancer:

Colonoscopy

During a colonoscopy, a doctor will insert a long, flexible tube with a camera on one end into the rectum to inspect the inside of the colon.

A person may have to follow a special diet before the procedure, such as a clear liquid diet 1–3 days beforehand. The colon will also require cleansing with strong laxatives in a process known as bowel prep.

If the doctor finds polyps in the colon, a surgeon will remove them and send them for biopsy. In a biopsy, a pathologist examines the polyps under a microscope to look for cancerous or precancerous cells.

A similar procedure, called a flexible sigmoidoscopy, allows a doctor to examine a smaller portion of the colorectal area. This method does not reach as far as a colonoscopy. Also, a full colonoscopy may not be necessary if a sigmoidoscopy does not reveal polyps or if they are only within a small area.

Learn how to prepare for a colonoscopy here.

Double-contrast barium enema

This X-ray procedure uses a liquid called barium to provide clearer images of the colon than a standard X-ray. A person may need to avoid eating or drinking before undergoing a barium X-ray.

A doctor will inject a liquid solution containing the element barium into the colon through the rectum. They follow this with a brief pumping of air to smooth over the barium layer to provide the most accurate results.

A radiologist will then conduct an X-ray of the colon and rectum. The barium appears white on the X-ray, and any tumors and polyps will appear as dark outlines.

If a biopsy suggests the presence of colon cancer, the doctor may order a chest X-ray, an ultrasound, or a CT scan of the lungs, liver, and abdomen to assess the spread of cancer.

Following diagnosis, a doctor will determine the stage of the cancer based on the size and extent of the tumor and the spread to nearby lymph nodes and distant organs.

The stage of a person’s cancer will determine their treatment options and inform their outlook.

Learn about other diagnostic tests for colon cancer here.

There is no guaranteed way to prevent colon cancer. However, some preventive measures may include:

People should also consider limiting their alcohol consumption and quitting smoking.

Screening

Symptoms may not appear until cancer has progressed. For this reason, the American College of Physicians recommends screening for people aged 50–75 years, including fecal testing once every 2 years, a colonoscopy every 10 years, or a sigmoidoscopy every 10 years plus fecal testing every 2 years.

The regularity of screening depends on an individual’s level of risk. People can consult their doctor for personal recommendations.

The ACS calculates a person’s likely chance of survival using a 5-year survival rate depending on the stage of colon cancer:

  • localized: 91%
  • regional: 72%
  • distant: 14%
  • all stages combined: 63%

However, these survival rates are from 2010–2016, and treatment and research are continually advancing. Early detection and treatment are the most effective ways to improve the outlook of a person with colon cancer.

Colon cancer is a type of colorectal cancer. It means that there is a cancerous growth in the colon.

Signs of colon cancer may not be obvious in its earlier stages. However, they may include pain, rectal bleeding, or blood in the stool.

There are many treatment options for colorectal cancer. These include chemotherapy, radiation therapy, and surgery.