Colorectal cancer, also known as bowel cancer, colon cancer, or rectal cancer, is any cancer that affects the colon and rectum.

The American Cancer Society (ACS) expects to see around 104,270 new cases of colon cancer and 45,230 new cases of rectal cancer in the United States in 2021.

Colorectal cancer is the third most common cancer in the U.S. and the second cause of cancer-related deaths.

The incidence varies around the world. It is more common in countries with a higher economic status, but according to a 2021 analysis, it is also more likely to affect individuals with a low income.

Fatality rates have been falling due to medical advances. Also, the 2021 analysis observes that numbers of diagnoses are rising among people younger than 50 years old, possibly due to improvements in screening.

In this article, learn about the symptoms of colorectal cancer and the treatments. Also, find out about the risk factors, some of which are avoidable.

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Illustration by Diego Sabogal

Colorectal cancer may not cause symptoms in the early stages. If it does, they may include:

  • changes in bowel habits
  • diarrhea or constipation
  • a feeling that the bowel does not empty properly
  • blood in feces that makes it look dark brown or black
  • bright red blood from the rectum
  • abdominal pain and bloating
  • feeling full, even when a long time has passed since a meal
  • fatigue or tiredness
  • unexplained weight loss
  • anemia

If a doctor finds signs of anemia during a routine medical check, they may suggest screening for colorectal cancer. Others receive the diagnosis after routine screening. Around 40% of people with this type of cancer receive the diagnosis when the disease is in an early stage.

The symptoms can be similar to those of many other health conditions. Anyone who has concerns about these symptoms should seek medical advice.

Among people who receive a diagnosis of colorectal cancer after reporting symptoms:

  • 37% have blood in feces or from the rectum
  • 34% have abdominal pain
  • 23% have anemia

Among those who receive the diagnosis after seeking emergency medical assistance:

  • 57% have a blockage in their bowel
  • 25% have peritonitis, or inflammation of the stomach lining
  • 18% have a perforation, or hole, in their bowel

Some people only notice symptoms in the later stages, when the cancer has spread to the lungs, liver, or other areas. The symptoms can depend on the area affected.

If cancer spreads to the liver, a person may have jaundice, which causes yellowing of the whites of the eyes. If a person has white or light brown skin, it may also appear yellowish. If cancer affects the lungs, the person may have difficulty breathing or a cough.

Does Medicare cover screening for colorectal cancer?

Treatment will depend on several factors. These include:

  • the size and location of tumors, and the cancer’s stage
  • whether the cancer is recurrent
  • the person’s overall health

Treatment options include chemotherapy, radiation therapy, and surgery. Palliative care can help manage symptoms, such as pain, and improve the quality of life.

Surgery

Surgery is the primary treatment for colorectal cancer that is limited to the colon. It aims to remove cancerous tissue, including tumors and nearby lymph nodes, and prevent the cancer from spreading.

The surgeon usually sews the bowel back together, but they may need to insert a stoma and colostomy bag for drainage. This is often temporary.

Surgery may remove all traces of early stage cancer. In the later stages, surgery cannot stop the cancer from spreading, but removing a blockage can help ease any symptoms.

Chemotherapy

Chemotherapy drugs destroy cancerous cells throughout the body. This may help treat colon cancer or shrink a tumor before surgery. It can also help relieve symptoms in the later stages.

This approach, however, can have widespread adverse effects, as it targets both cancerous and healthy cells.

Targeted therapy

This involves taking drugs that target specific proteins to slow or prevent the growth of cancerous cells.

The adverse effects are usually less severe than those of chemotherapy because these drugs only target specific cells.

Immunotherapy

This drug treatment helps the body use its immune system to detect and eliminate cancerous cells. It may help some people with advanced colorectal cancer.

Possible adverse effects include an autoimmune reaction, in which the body mistakenly attacks its own cells.

Radiation therapy

Radiation therapy uses high-energy radiation beams to destroy cancerous cells and prevent them from multiplying.

A doctor may recommend it to help shrink a tumor before surgery for rectal cancer. They may also use it alongside chemotherapy, in an approach known as chemoradiation.

It can have long- and short-term adverse effects.

Ablation

Ablation involves using microwaves, radiofrequency, ethanol, or cryosurgery to destroy a tumor without removing it.

A surgeon delivers the therapy using a probe or needle guided by ultrasound or CT scans.

Palliative and end-of-life care

If colorectal cancer spreads to organs beyond the colon, progressing to stage 4, it is not possible to cure it. Other options may include:

  • surgery to remove a blockage
  • radiation therapy or chemotherapy to reduce the size of tumors
  • pain relief
  • treatment for side effects of medication
  • counseling

In the future: Vaccines

Scientists are hopeful that a vaccine to treat colorectal cancer will soon become available.

Clinical findings published in 2019 concluded that one vaccine, called Ad5-GUCY2C-PADRE, may help people with colorectal cancer that has not yet reached stage 3.

It is not clear exactly why colorectal cancer occurs. Most cases probably result from a combination of environmental and genetic factors.

Around 70% of cases happen for no clear reason, while 10% appear to be inherited and 20% happen in family clusters.

Some other associated factors may include:

  • being of older age
  • being male
  • having a low income
  • having a diet low in fiber and high in animal protein, saturated fats, and calories
  • having a diet high in red or processed meats
  • consuming alcohol
  • smoking
  • getting low levels of physical activity
  • being overweight or having obesity
  • having inflammatory bowel disease
  • having type 2 diabetes
  • having certain genetic features
  • having had breast, ovary, or uterine cancer
  • having undergone radiation therapy for abdominal cancer in childhood
  • having polyps in the colon or rectum

Polyps are sometimes precancerous. Learn about one type, called sessile polyps, that can develop in the colon.

Black Americans have a higher risk

Research from 2018 concludes that Black Americans are more likely to develop and die from colorectal cancer than any other group in the U.S.

The chance of a Black person having this type of cancer is at least 20% higher than the chance of a white person having it, and the fatality rate is 40% higher for Black people, the ACS report.

Explaining the reasons, the ACS cites socioeconomic factors and inequity in terms of screening specifically and healthcare generally, as well as employment, diet, and other factors related to daily life.

The authors of the 2018 analysis say that further research is needed to identify whether colorectal cancer affects Black people in specific ways, and they note that this investigation might lead to more effective treatment.

What is health inequity? Learn more here.

The stage of cancer refers to how far it has spread. Determining the stage helps doctors chose the most appropriate treatment.

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There are different methods of staging. One method is:

  • Stage 0: This is the earliest stage, also known as carcinoma in situ, when the cancer is only in the inner layer of the colon or rectum.
  • Stage 1: The cancer has grown through the inner layer of the colon or rectum but has not spread beyond the wall of the rectum or colon.
  • Stage 2: The cancer has grown through or into the wall of the colon or rectum but has not yet reached nearby lymph nodes.
  • Stage 3: The cancer has reached nearby lymph nodes but not other parts of the body.
  • Stage 4: The cancer is present in other parts of the body, such as the liver or lungs.

Sometimes, treatment eliminates the cancer, but it comes back in the same area or another part of the body. This is called recurrent cancer.

Screening can detect polyps before they become cancerous. It can also detect colon cancer in the early stages, when it is easier to treat.

In 80% of cases, a doctor diagnoses colorectal cancer after performing a colonoscopy because the person has symptoms. Routine screening detects 11% of cases, and 7% of people with colorectal cancer receive a diagnosis after seeking emergency care for sudden abdominal symptoms.

The following are the most common screening and diagnostic procedures for colorectal cancer.

Colonoscopy

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Colonoscopy is the gold standard diagnostic tool for colorectal cancer. It has a high level of accuracy and can show precisely where a tumor is.

The procedure involves using a long, thin, flexible tool called a colonoscope that contains a light and a camera. It allows the doctor to see the whole colon and rectum. They may also remove polyps or take tissue for a biopsy during the procedure.

A colonoscopy is painless, but some people take a mild sedative to help them stay calm. Beforehand, a person may need to drink a laxative fluid to clean out their colon. Bleeding and perforation of the colon wall are rare but possible complications.

Blood stool test

This checks for blood in a stool sample. This issue can result from many conditions — it does not mean that cancer is present. A person can take their stool sample at home or at work.

Stool immunochemistry

Also known as a fecal immunochemistry test, this checks for hidden blood in the lower colon. It involves using a small kit to collect a stool sample at home.

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Stool DNA test

This test checks for several DNA markers that colon cancers or precancerous polyps shed into stool. A person collects an entire bowel movement at home for testing in a lab. If the result is positive, a colonoscopy is necessary.

It is worth keeping in mind that this test cannot detect every DNA marker of cancer.

Flexible sigmoidoscopy

This procedure involves using a sigmoidoscope, a flexible, thin, lighted tube, to examine the rectum and sigmoid colon — the last part of the colon before the rectum.

The test takes a few minutes and is not painful, but it might be uncomfortable. There is a small risk of perforating the colon’s wall.

Barium enema X-ray

Barium is a contrast dye that can reveal any unusual features on an X-ray. A healthcare professional introduces it into the bowel as an enema.

A doctor may recommend a colonoscopy for closer investigation following a barium enema X-ray.

CT colonography

This produces images of the colon. It is less invasive than a colonoscopy, but if it reveals a mass, the person will need a colonoscopy.

Imaging scans

Ultrasound, CT, or MRI scans can show if cancer has spread to another part of the body.

Learn more about tests other than a colonoscopy that can detect colorectal cancer

The outlook for someone with colorectal cancer depends on many different factors, including their age, their overall health, and the stage at which the cancer was diagnosed.

The ACS provides 5-year survival rates. These reflect the likelihood of living for at least another 5 years after the diagnosis, compared with a person who does not have colorectal cancer.

The ACS gives survival rates using these stages:

  • Local: The cancer has stayed in its original location.
  • Regional: The cancer has spread to nearby tissues.
  • Distant: It has reached more distant parts of the body.

This table shows the estimated 5-year survival rates for a person with colon cancer.

Stage5-year survival rate
Stage 1 (local)91%
Stage 2 (regional)72%
Stage 3 (distant)14%
Overall63%

This table shows the estimated 5-year survival rates for a person with rectal cancer:

Stage5-year survival rate
Stage 1 (local)89%
Stage 2 (regional)72%
Stage 3 (distant)16%
Overall67%

According to a 2010 report from the National LGBT Cancer Network, the risk of dying from colorectal and other types of cancer may be higher for gay men due to challenges in accessing appropriate healthcare.

Here, learn more about the life expectancy for people with stage 4 colon cancer.

Colorectal cancer can affect anyone, and it is not possible to prevent it. However, some measures may help reduce the risk.

Screening

Current guidelines from the American College of Physicians recommend regular screening for people who:

  • have a personal or family history of colorectal cancer
  • are Black Americans aged 45 years or over
  • are not Black, over 50, and have an average risk
  • have Crohn’s disease, Lynch syndrome, or adenomatous polyposis

A doctor will recommend a specific schedule of screening. For example, they may recommend a stool test every 2 years and a colonoscopy or sigmoidoscopy every 10 years.

Nutrition

Dietary measures that may help reduce the risk include:

  • eating plenty of fiber, fruits, and vegetables
  • eating quality carbohydrates
  • limiting the intake of red and processed meats.
  • opting for healthy fats, such as avocados, olive oil, fish oils, and nuts, instead of saturated fats

Exercise and weight

Moderate, regular exercise may help lower the risk of colorectal cancer. Exercise can also help reduce the risk of obesity, which is linked with colorectal and other cancers.

Aspirin

Experts have found that taking aspirin may help reduce the risk in some people, but speak with a doctor about this first.

Vaccines

Researchers are investigating the potential for vaccines to prevent colorectal cancer. One option that has been successful in mice is a vaccine that stops polyps from becoming cancerous. This might one day help people with a high risk.

Colorectal cancer is a common type and a leading cause of cancer-related death. Treatment in the early stages can remove cancerous cells and increase the chances of a positive outcome.

However, symptoms may not appear until the later stages. Anyone with a risk of developing colorectal cancer should ask a doctor about screening. Having regular screening improves the chances of an early diagnosis.