Bowel Health

What is bowel cancer?

Written by

Lauren Dobischok
27 December, 2022

Medically checked article All HOMED-IQ content is reviewed by medical specialists

Bowel cancer is cancer that begins in the large bowel (colon) or rectum, and is one of the most common cancers in the world (Rawla et al., 2019). In 2020, there were more than 1.9 million new cases of bowel cancer recorded globally (Xi & Xu, 2021). Bowel cancer is sometimes called colon or colorectal cancer. Although bowel cancer can be a serious illness, if detected early it is highly treatable and requires less invasive interventions. In order to catch bowel cancer early, several screening tests have been designed to check for polyps or changes in the bowel that could be cancerous. 

What is bowel cancer?

Bowel cancer occurs when cancer cells develop in the colon or rectum. It usually begins as small, noncancerous lumps of cells called polyps that form on the walls of the intestines. Over time, these polyps can develop into cancer (Mayo Clinic, 2022). It is important to note that not all polyps will turn into cancer, and the risk of a polyp becoming cancerous depends on what type it is. The type of bowel polyp that is more likely to be precancerous is called an adenoma (University of Michigan). Bowel polyps are more common in older adults, which is why this age group is targeted for screening.

The different types of bowel cancer

Bowel cancer affects the colon (large intestine) or rectum (passageway from the colon to the anus). The type of cancer that develops depends on the cell it starts in. Most colorectal cancers are adenocarcinomas, meaning they start in cells that produce mucus to lubricate the walls of the colon and rectum (American Cancer Society, 2022). Other types of colorectal cancer are much more rare. These include:

  • Carcinoid tumours: arise from hormone-making neuroendocrine cells
  • Sarcomas: occur in connective tissues in the walls of the colon or rectum
  • Gastrointestinal stromal tumours: occur in special cells in the digestive tract, rarely in the colon or rectum
  • Lymphomas: begins in the cells of the lymph system, which can include the colon or rectum

Source: American Cancer Society, 2022

How does bowel cancer develop?

Bowel cancer usually begins as a noncancerous polyp in the wall of the colon or rectum. Over time (usually several years), this polyp can become cancerous. This means the cells in the polyp begin to divide uncontrollably, forming a tumour (American Cancer Society, 2022). Bowel polyps develop spontaneously on the walls of the intestines and usually are only a few millimetres in size. Checking the colon and rectum for polyps and removing them before they become cancer is an effective way to prevent colorectal cancer. While not all colorectal polyps will become cancer, removing them is required to check whether they are a type that could become cancer.

Symptoms of bowel cancer

Bowel cancer often does not cause symptoms in the early stages of disease. That is why early detection and prevention is so important. Potential symptoms include:

  • Stool containing blood or mucus
  • Change in frequency or consistency of stool
  • Decrease in appetite
  • Unintentional weight loss
  • Abdominal pain or intestinal cramps
  • Feeling as if the bowel does not empty completely
  • Fatigue

Source: Mayo Clinic, 2022

How common is bowel cancer?

Bowel cancer is the third most common cancer worldwide, and is one of the most common cancers in Europe. It is estimated 340,000 people in the EU were diagnosed with colorectal cancer in 2020 (OECD). Most people with colorectal cancer are over age 50, but incidence is increasing in younger adults (NIH, 2020).

Risk factors for bowel cancer

The main risk factor for bowel cancer is age. Most bowel cancer cases occur in people aged 50 or older (, 2022) Other risk factors include:

  • A family history of bowel cancer or polyps
  • Being overweight or obese
  • Lack of physical activity
  • Inflammatory bowel diseases, such as Crohn’s or ulcerative colitis
  • A diet low in fruit or vegetables
  • A high fat, low fibre diet
  • Alcohol and tobacco use
  • Certain genetic syndromes (i.e. Lynch Syndrome)

Source: Mayo Clinic, 2022

How do you test for bowel cancer?

There are several bowel cancer screening tests available. One screening option is a fecal occult blood test (FOBT) or fecal immunochemical test (FIT). These tests check for hidden blood in the stool that may be caused by polyps or cancer (, 2022). FOBT and FIT tests can be performed from home, and are used in many countries’ national bowel cancer screening programs. A home test requires the user to collect a stool sample using a collection kit and mail it to a laboratory for analysis. Homed-IQ’s Bowel Cancer Test is an FIT test that can be performed entirely from home. FOBT and FIT tests should be repeated every 1-2 years. 

Other screening tests for bowel cancer include physically examining the colon/rectum and removing polyps or tissue where needed. A sigmoidoscopy involves examining the lower colon and rectum using a lighted tube. A colonoscopy examines the entire colon and rectum for polyps or abnormalities (, 2022). Sigmoidoscopies and colonoscopies do not have to be repeated as often as stool tests. If there is an abnormal result on any sigmoidoscopy or stool test, you will be referred for a colonoscopy. 

Different screening tests may be used depending on your personal risk of cancer and should be discussed with your doctor. Screening type, frequency, and eligible age group may also vary by country. No matter what testing method is chosen, getting screened regularly is the most important thing.

When should I visit the doctor?

If your fecal occult blood test result is positive, visit your doctor for follow-up care. A colonoscopy is likely needed to investigate further. If your test results are negative but you are experiencing symptoms that could indicate bowel cancer or have a family history of the disease, see your doctor to discuss if additional screening is needed. 

Diagnosing bowel cancer

If your fecal occult blood test result is positive, you will be referred for an examination of the colon (colonoscopy). During this exam, polyps and tissue may be removed and examined to check for cancer cells. After cancer is diagnosed, MRI or CT scans may be used to stage the cancer and check if it has spread elsewhere (NHS, 2021).

Treatment of bowel cancer

Treatment of bowel cancer depends on where the cancer is found and if it is spread. Surgery to remove the affected part(s) of the colon or rectum is usually the first step in treatment (NHS, 2021). This may be combined with chemotherapy, radiation therapy, or other treatments depending on where the cancer has spread. 


American Cancer Society. (2020). What Is Colorectal Cancer? | How Does Colorectal Cancer Start?

Colon and Rectal Polyps | Michigan Medicine. (n.d.).

Colon cancer – Symptoms and causes. (2022, October 8). Mayo Clinic.

Colorectal Cancer – Risk Factors and Prevention. (2022, November 17). Cancer.Net.

Colorectal Cancer Rising among Young Adults. (2020, November 5). National Cancer Institute.

NHS website. (2021, December 8). Diagnosis.

OECD. (n.d.). Health at a Glance: Europe 2020 : State of Health in the EU Cycle. OECD iLibrary.

Rawla, P., Sunkara, T., & Barsouk, A. (2019). Epidemiology of colorectal cancer: incidence, mortality, survival, and risk factors. Gastroenterology Review, 14(2), 89–103.

Xi, Y., & Xu, P. (2021). Global colorectal cancer burden in 2020 and projections to 2040. Translational Oncology, 14(10), 101174.

About the author

Lauren Dobischok

Lauren is a health scientist and science communicator currently living in the Netherlands. Originally from Canada, she completed a Research Master’s in Health Sciences at the Netherlands Institute of Health Sciences at Erasmus University Rotterdam (NIHES) with a specialisation in epidemiology. Prior to her master’s degree, she completed a Bachelor’s degree in Health Sciences at Simon Fraser University. With a background in public health, her goal is to create accurate scientific content that is easy to understand and empowers people to make informed decisions. Within Homed-IQ, Lauren works as a Product Developer and Content Lead, working closely with physicians and scientists on medical devices for Homed-IQ’s new products and written communications.