What Is Colon Cancer?

  • 1st Revision: Patrick Ezeani

Colon cancer is among the most common cancer types in both women and men. colon cancer can affect all ages but occurs more frequently in older adults.

Colon cancer is caused by uncontrolled growth of cells in the large bowel (colon) or rectum. It is also known as colorectal cancer. It is responsible for many deaths worldwide. However most people with colon cancer do not develop symptoms or develop late. Therefore, it is very important to know the risk factors and early signs and symptoms of colon cancer as well as screening programmes available. as early detection makes a huge difference for management of the disease, quality of life and survival. Risk factors are another important subject when it comes to colon cancer. Being aware of those risk factors and taking precautions might decrease your risk of having colon cancer in the future include older age (50 years and above), race (African-American), positive family history, sedentary lifestyle and dietary habits (low fiber, high fat).

Colorectal cancer is a serious public health concern, affecting millions of people worldwide. It is the third most common type of cancer globally, with an estimated 2 million new cases diagnosed in 2020. It is also the second leading cause of cancer deaths, resulting in approximately 1 million deaths each year.12

Colorectal cancer affects thousands of people each year and it is the fourth most common type of cancer in the UK, with an estimated 42,900 new cases diagnosed each year.13


Colorectal cancer is the cancer of the colon or rectum. These  cancers can also be called colon cancer or rectal cancer, depending on the site. Due to having similar presentations, colon cancer and rectal cancer are often grouped together.

The colon and rectum come together to make up the large intestine or large bowel. Large intestine is part of the digestive system, also called gastrointestinal system.Colon is a muscular tube with a size of approximately 5 feet (1.5 meters). It has 4 parts which are named as ascending colon, transverse colon, descending colon, and sigmoid colon. Ascending colon is closer to the small intestine and the sigmoid colon is closer to the rectum and back passage. Food travels from ascending colon to sigmoid colon. 

The function of the colon is to absorb water and salt from the remaining food matter after it goes through the small intestine. After passing through the colon, the waste matter goes into the rectum which is the 6 inches (15 cm) final part of the digestive tract. The rectum is the storage place for the waste matter before it passes through the anus. When there is a bowel movement, ring-shaped muscles (also called a sphincter) around the anus relax and let the passage of stool through anus.1

Causes of colon cancer

Colon cancer is caused by mutation or change in the specific genes of the DNA, just like any other types of cancer. Depending on the mutation, colorectal cancers can be acquired, inherited or familial.2

Oncogenes help our cells to grow, divide and stay alive. Tumor suppressor genes control cell division and lead cells to die at the right time. If oncogenes are turned on or tumor suppressor genes are turned off by a mutation in our DNAs, it results in uncontrolled growth of the cells followed by cancer.

Some of the mutations in the DNA can be passed on in families. These are called inherited mutations. Inherited colorectal cancers make up a very small part of all colorectal cancers. Some inherited colorectal cancers include familial adenomatous polyposis (FAP), Gardner syndrome, Lynch syndrome (hereditary non-polyposis colon cancer, or HNPCC), and Peutz-Jeghers syndrome.

Most colorectal cases are caused by acquired mutations. These mutations are possibly a result of certain risk factors and are not passed on to subsequent generations.2

Signs and symptoms of colon cancer

There are various symptoms suggestive of colon cancer. However, those symptoms might also be indicative of another condition. In that case, it is important to see a doctor to exclude the possibility of cancer.

Possible symptoms of colon cancer include:3

  • Bleeding from the back passage or blood in your poo
  • Change in your normal bowel habit, such as having diarrhea, constipation or pooping more often
  • A lump that your doctor can feel in your back passage or tummy, more commonly on the right side
  • A feeling of needing to strain in your back passage as if you need to poo, even after opening your bowels
  • Unexplained weight loss
  • Loss of appetite
  • Pain in your abdomen or back passage
  • Tiredness and breathlessness caused by a decreased amount of red blood cells (anemia)
  • Bowel obstruction symptoms due to cancer blocking the bowel such as cramping pains in the tummy, feeling bloated, constipation, being unable to pass the wind, being sick, and sometimes vomiting

Blood in the stool might be an alarming symptom for colon cancer. However, it could also be caused by other diseases. If the blood is fresh and bright, it is mostly caused by piles (hemorrhoids). Piles are swollen veins in the back passage. These fragile veins can easily get damaged during passing stool and might end up bleeding.

If the bleeding originated from a higher point in the large bowel, blood does not look bright red. The higher the bleeding point in the large bowel, the darker or black the blood in your stool becomes. Therefore, any darker blood could be a sign of cancer higher up the bowel or a bleeding stomach ulcer as another possibility.3

Management and treatment for colon cancer

In case of being diagnosed with colorectal cancer, your treatment options will be discussed with you by the cancer care team.

Depending on the treatment options, you might have different types of doctors and healthcare professionals on your care team. These doctors might include:

  • A gastroenterologist who treats disorders of the digestive tract
  • A surgical oncologist who operates on the cancer
  • A colorectal surgeon who operates on the diseases of the colon and rectum
  • A radiation oncologist who treats cancer with radiation therapy
  • A medical oncologist who treats cancer with medications such as chemotherapy or targeted therapy

Other healthcare professionals include physician assistants, nurse practitioners, nurses, psychologists, nutritionists, social workers, and others. 

Colorectal cancer treatment is based on the site, size, stage of the cancer, and your overall health.  There are different types of treatments available as local and systemic treatments.

Local treatments target the tumor without affecting the rest of the body. These treatments are more likely to be useful for smaller or earlier stage cancers. Surgery, ablation and embolization and radiation therapy are types of local treatment.

Systemic treatments target cancer cells almost all over the body. Chemotherapy, targeted therapy and immunotherapy are types of systemic treatment.

In order to make the decision for the most suitable treatment for you, it is important to discuss all the options as well as the aim and possible side effects of them. It is also very important to ask questions if there is anything you have on your mind. 

If you have time, it might be a good idea to get a second opinion for the treatment. A second opinion can provide you with more information and help you choose the best treatment option for you.4


How is colon cancer diagnosed

Warning symptoms and abnormal screening test results warrant further assessment by your doctor. There are several examinations and investigations that need to be done to confirm the diagnosis. Your doctor will recommend one or more of the exams and tests below to find the cause.

Medical history and physical exam: You will be asked about your symptoms, past medical history, family history as well as lifestyle to find out any possible risk factors. 

Your doctor will examine your whole body, including tummy for any masses or enlarged organs. You might also have a back passage examination called a digital rectal exam. It is done by your doctor inserting a lubricated and gloved finger into your rectum to feel for any abnormal areas.

Tests to detect blood in your stool: A fecal occult blood test is a simple test that checks for tiny amounts of blood in the stool, which can be a sign of colon cancer. 

Blood tests: Several blood tests are helpful to diagnose colorectal cancer. Those include:

  • Full blood count: It might show anemia which is one of the signs of colorectal cancer due to bleeding
  • Liver enzymes: Colorectal cancer might affect liver function tests because of spreading to the liver.
  • Tumor markers: Tumor cells might produce some substances that can be released into the blood. The most common tumor marker is carcinoembryonic antigen (CEA).They might increase in blood in case of cancer. However, they might be normal in some cancer cases and can increase without cancer. These markers can also help evaluate the efficacy of the treatment and provide an early warning in case of cancer return

Colonoscopy: This is a procedure in which a long, flexible tube with a camera on the end is inserted into the rectum to view the inside of the colon. The doctor can remove any abnormal growths or polyps during the procedure and send them for biopsy to examine under the microscope.

Proctoscopy: This is a procedure that involves the visual examination of the rectum and the lower part of the colon using a proctoscope, a lighted tube with a small camera on the end. The doctor can remove any abnormal growths or polyps during the procedure and send them for biopsy to examine under the microscope.

Imaging tests: They create pictures of the inside of the body to look for cancer, to find out how far cancer might have spread, to determine the efficacy of treatment, to look for signs of cancer returning after treatment. They include computed tomography (CT), ultrasound, magnetic resonance imaging (MRI) and positron emission tomography (PET) scans as well as x-ray scans.5

Can colon cancer be prevented

Cancer prevention aims to reduce the chances of developing cancer by decreasing the risk factors and increasing the protective factors. Some risk factors, such as genetic predisposition, can not be avoided, but certain lifestyle modifications, such as a healthy diet and regular exercise, can lower the risk of developing cancer. Avoiding known cancer-causing agents and taking medication for precancerous conditions are also effective ways to prevent cancer. However, even if all preventive measures are taken, cancer cannot be completely prevented.

Some protective factors to decrease the risk of colorectal cancer include:

  • Physical activity
  • Aspirin
  • Combination hormone replacement therapy
  • Polyp removal

The following factors do not affect the risk of colorectal cancer:

  • Hormone replacement therapy with estrogen only
  • Statins

Clinical trials are being conducted to explore new methods of preventing colorectal cancer.6

Although colon cancer can not be prevented completely, early detection of the cancer may improve survival rates and decrease the risk of death. Early detection is possible with colon cancer screening tests.

Screening tests are used to detect cancer before symptoms appear. Screening tests can also help in identifying people who are at higher risk for certain types of cancer and are therefore more likely to benefit from early detection and treatment.

Research is ongoing to determine the most effective screening tests for different types of cancer and to identify the populations that are most likely to benefit from them. It's important to keep in mind that a positive screening test result does not necessarily mean you have cancer, but it may require further diagnostic tests to confirm the presence of cancer.7

There are five types of tests available to screen for colorectal cancer screening. These include:7

  • Fecal occult blood test (FOBT): This is a test to check for hidden blood in stool.There are two types available. One is guaiac FOBT and the other is fecal immunochemical test or FIT. 
  • Sigmoidoscopy: This is a type of screening test used to examine the inside of the rectum and lower part of the colon, also known as the sigmoid colon, for any signs of polyps, abnormal areas, or cancer.
  • Colonoscopy
  • Virtual colonoscopy: It uses a series of x-rays and computer technology to create detailed images of the inside of the colon.
  • DNA stool test: It looks for DNA in stool cells for genetic changes which might be indicative of colorectal cancer.

Who are at risks of colon cancer

Many personal traits or habits are considered to be risk factors for colon cancer. Because they increase the chances of developing polyps or colon cancer.

The most important risk factor for colon cancer is age. Risk of having colon cancer is significantly increased after 50 years old. On the contrary, colon cancer is rare in people who are below 50 years old except for the inherited cases.8

The following risk factors increase the colorectal cancer risk:6,9

  • Age
  • Family history 
  • Previous colorectal cancer
  • High risk adenomas (polyps that are 1 cm or larger in size or that have abnormal cells)
  • Male sex
  • Ovarian cancer
  • Inflammatory bowel disease such as ulcerative colitis or Crohn disease
  • Inherited genes
  • Alcohol
  • Cigarette smoking
  • African American ethnicity
  • Obesity
  • Sedentary lifestyle
  • Red meat and processed meat
  • History of Radiation to abdomen
  • Acromegaly
  • Renal Transplant with use of immunosuppressive medications
  • Diabetes mellitus type 2 and insulin resistance
  • Androgen deprivation therapy
  • Gallbladder removal
  • Coronary artery disease
  • Ureterocolic anastomosis (connection between ureter and the colon)

What are the stages of colon cancer

Staging is an important factor in determining the appropriate treatment for bowel cancer. The stage of bowel cancer indicates how far the cancer has grown through the bowel wall and whether it has spread to lymph glands or other parts of the body. This information helps the doctor determine the best treatment plan.

There are different ways to stage bowel cancer such as tumour, node and metastasis (TNM) staging system and number staging system.

The type and grade of a bowel cancer refer to the characteristics of the cancer cells. The type indicates the type of cell the cancer started in and where it began, while the grade describes how abnormal the cells look under a microscope. The type and grade can help predict the behavior of the cancer and guide treatment decisions.10

How common is colon cancer

According to WHO, cancer is the second leading cause of death worldwide. In 2018, one in six deaths was caused by cancers. Most common cancer types among men are lung, prostate, colorectal, stomach and liver cancer. On the other hand, most common cancer types in women are breast, colorectal, lung, cervical and thyroid cancer.11

Colorectal cancer is a serious public health concern, affecting millions of people worldwide. It is the third most common type of cancer globally, with an estimated 2 million new cases diagnosed in 2020. It is also the second leading cause of cancer deaths, resulting in approximately 1 million deaths each year.12

Colorectal cancer affects thousands of people each year and it is the fourth most common type of cancer in the UK, with an estimated 42,900 new cases diagnosed each year.13

Colorectal cancer is more commonly diagnosed in Western countries, with about 55% of all cases occurring in these regions. However, the trend is changing as some developing countries are experiencing a rapid increase in the incidence of colorectal cancer. Despite this, only 33% of all colorectal cancer-related deaths in the world occur in Western countries, indicating that improvements in health systems and the implementation of screening programs have been effective in reducing death rates from this disease.8

When should I see a doctor

If you are experiencing any of the symptoms of colorectal cancer such as blood in stool, change in normal bowel habit, lumps or bumps in the body, weight loss, tummy or back passage pain or tiredness, it's important to see your GP for an evaluation, as these symptoms can be caused by a variety of conditions, including non-cancerous ones like piles, infections, or inflammatory bowel disease.

Bowel obstruction which might be caused by cancer is an emergency condition. If you experience any of the symptoms suggestive of bowel obstruction such as tummy cramps, bloating, constipation and unable to pass wind, please seek medical attention immediately.

While it's natural to be concerned about the possibility of cancer, it's important to remember that many cases of colorectal cancer can be treated successfully, especially if the cancer is detected early. So, don't be afraid to talk to your doctor about any symptoms you are experiencing, as prompt evaluation and treatment can help improve your chances of a positive outcome.3


Colon cancer is one of the most common cancers in the world. It is also one of the leading causes of cancer deaths, affecting many lives. 

Possible symptoms of colon cancer include blood in stool, bleeding from back passage, change in bowel habits and weight loss.

Even though it is not possible to prevent colon cancer completely, there is a possibility to decrease the risk by avoiding certain risk factors or adopting protective factors into our lifestyles.

Certain risk factors that increase colorectal cancer risk include age, family history, previous colon cancer, high risk adenomas and male sex.

Diagnosis is made through medical history and physical examination as well as certain investigations such as blood tests, fecal occult blood test and colonoscopy.

Colorectal cancer treatment is based on the site, size, stage of the cancer, and your overall health. Surgery, chemotherapy, radiotherapy or immunotherapy are among the options.

Early detection of colon cancer with screening tests may improve survival rates and decrease the risk of death. Therefore, it is crucial to get screened through bowel cancer screening programme available in many countries.


  1. What is colorectal cancer? | how does colorectal cancer start? [Internet]. [cited 2023 Feb 14]. Available from: https://www.cancer.org/cancer/colon-rectal-cancer/about/what-is-colorectal-cancer.html
  2. Colorectal cancer causes & risk factors | colorectal cancer prevention [Internet]. [cited 2023 Feb 14]. Available from: https://www.cancer.org/cancer/colon-rectal-cancer/causes-risks-prevention.html
  3. Symptoms of bowel cancer | cancer research uk [Internet]. [cited 2023 Feb 14]. Available from: https://www.cancerresearchuk.org/about-cancer/bowel-cancer/symptoms
  4. Colorectal cancer treatment | how to treat colorectal cancer [Internet]. [cited 2023 Feb 14]. Available from: https://www.cancer.org/cancer/colon-rectal-cancer/treating.html
  5. Testing for colorectal cancer | how is colorectal cancer diagnosed? [Internet]. [cited 2023 Feb 14]. Available from: https://www.cancer.org/cancer/colon-rectal-cancer/detection-diagnosis-staging/how-diagnosed.html
  6. Colorectal cancer prevention (Pdq®)–patient version - nci [Internet]. 2022 [cited 2023 Feb 14]. Available from: https://www.cancer.gov/types/colorectal/patient/colorectal-prevention-pdq
  7. Colorectal cancer screening (Pdq®)–patient version - nci [Internet]. 2022 [cited 2023 Feb 14]. Available from: https://www.cancer.gov/types/colorectal/patient/colorectal-screening-pdq
  8. Mármol I, Sánchez-de-Diego C, Pradilla Dieste A, Cerrada E, Rodriguez Yoldi MJ. Colorectal carcinoma: a general overview and future perspectives in colorectal cancer. Int J Mol Sci [Internet]. 2017 Jan 19 [cited 2023 Feb 14];18(1):197. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5297828/
  9. Thanikachalam K, Khan G. Colorectal cancer and nutrition. Nutrients [Internet]. 2019 Jan 14 [cited 2023 Feb 14];11(1):164. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6357054/
  10. Stages, types and grades of bowel cancer | Cancer Research UK [Internet]. [cited 2023 Feb 14]. Available from: https://www.cancerresearchuk.org/about-cancer/bowel-cancer/stages-types-and-grades
  11. Cancer [Internet]. [cited 2023 Feb 14]. Available from: https://www.who.int/health-topics/cancer
  12. Colorectal cancer – IARC [Internet]. [cited 2023 Feb 14]. Available from: https://www.iarc.who.int/cancer-type/colorectal-cancer/
  13. What is bowel cancer? | Cancer Research UK [Internet]. [cited 2023 Feb 14]. Available from: https://www.cancerresearchuk.org/about-cancer/bowel-cancer/about-bowel-cancer
This content is purely informational and isn’t medical guidance. It shouldn’t replace professional medical counsel. Always consult your physician regarding treatment risks and benefits. See our editorial standards for more details.

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Ezgi Uslu Icli

Medical Doctor - Gazi University Medical School, Turkey

Ezgi has completed her studies in Medicine in 2017. After graduation, she worked as an emergency doctor followed by work experience as a research assistant in public health as well as undersea and hyperbaric medicine. She worked actively in the frontline during the COVID-19 pandemic as well.
She is passionate about medical writing as it helps increase health literacy and awareness of the public.
She moved to the UK in 2022 and she works as a volunteer in one of the NPOs for children in need.

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