Colorectal cancer

What is colorectal cancer?

Colorectal cancer is the presence of malignant or cancerous cells in the colon or rectum. Depending on where these cells originate, they may also be referred to as simply colon cancer or rectal cancer. Since they share a large number of characteristics, colon and rectal cancer are often grouped together. [1,2,3]

The colon makes up most of the large bowel (also called the large intestine), while the rectum is the terminal section of the large bowel which connects to the anus.1 Although colon cancer can occur at any age, it is cancer that typically affects older adults. [2]

The Cancer Association of South Africa (CANSA) reports that colorectal cancer is the number 2 cancer affecting men in our country while it is the number 3 cancer for women. According to their estimates, 1 in 79 men in South Africa will develop it. [4]

What causes colorectal cancer?

When the cells that line the inner part of the colon or rectum start to multiply uncontrolled, cancer may develop. [3] When it comes to colorectal cancers, the majority begins as small, protruding growths that are called “polyps”. Not all polyps will progress to cancer, and some may remain in the colon for years without causing harm. Others may turn into cancer over time. There are several different types of polyps and not all carry the same cancer risk, but in general, the risk of cancer is increased if a polyp is larger than 1 cm, if there are more than 3 polyps or if there are abnormal cells found with microscopic examination following a biopsy. The term “dysplasia” is used to describe the presence of such abnormal, precancerous cells. [1,2,3,4,5]

It may take between 10 to 15 years for abnormal cells to grow into polyps and then to develop into colorectal cancer. [5] Once cancerous, the cells can grow into (or invade) the wall of the colon or rectum. As the cancerous lesion grows within the wall, the cells may invade blood or lymph vessels from where the cells can travel to nearby lymph nodes or to more distant organs or body regions. [1]

Most colorectal cancers originate in cells that make mucous lubricate the inside of the colon and rectum and are called adenocarcinomas. However, there are also other types of cancers that can stem from other cells inside the colon, but these will be named after their origin (e.g., lymphoma if it originates in lymph nodes/tissues) and they are not called colorectal cancers. [1]

Risk factors

Those you may be able to control (at least to some extent)

If any of the following holds true for you, you might have a higher risk of developing cancer of the colon and/or rectum:

  • Low-fibre, high-fat diet [2,3,5]
  • Obesity [2,3,5]
  • Smoking [2,3,5]
  • Heavy use of alcohol [2,3,5]
  • A sedentary lifestyle. [2,3,5]

Those outside your control

  • Older age – most people with colorectal cancer are older than 50 years, but it should be borne in mind that colorectal can be diagnosed at any age [2,3,5]
  • A history of previous colorectal cancer or polyps [2,3,5]
  • Inflammatory bowel diseases, such as ulcerative colitis or Crohn’s disease [2,3,5]
  • Family history of colon cancer [2]
  • Diabetes [2,3,5]
  • Radiation therapy for cancer [2]
  • Certain inherited syndromes are caused by gene mutations and that are passed through generations in families – these include familial adenomatous polyposis (FAP) and Lynch syndrome, which is also known as hereditary nonpolyposis colorectal cancer (HNPCC). [2,3,5]

Please keep in mind that, even should you have one or more of these risk factors, you are not destined to develop colorectal cancer. [3] It is important that you go for regular check-ups to screen for it.

How can colorectal cancer be prevented?

It is generally recommended that people with an average risk of colorectal cancer initiate screening from approximately 45 to 50 years of age. People with an increased risk (such as those with a family history of colorectal cancer or with inflammatory bowel disease) should, however, consider screening at an earlier age. [2,4,6]

There are several screening options and your doctor will be able to help you decide which tests are most appropriate for you.2 Screening is important because if colorectal cancer is picked up at its earliest stage, it provides the greatest chance for a cure.6 Screening can be done with a colonoscopy (see How is colorectal cancer diagnosed), testing for occult blood in the stool, faecal DNA tests, and barium enemas, amongst others. [3,4]

Apart from regular screening, certain lifestyle changes may also assist you with reducing your risk of developing colorectal cancer. These include:

  • Ensuring that your diet contains a variety of fruits, vegetables, and whole grains [2,4,5]
  • Drinking alcohol in moderation or not at all [2,4,5]
  • Stop smoking [2,4,5]
  • Exercising most days of the week [2,4,5]
  • Maintaining a healthy weight. [2,4,5]
  • What are the signs and symptoms of colorectal cancer?

In the early stages, colorectal cancer may be asymptomatic; in other words, there may be a complete absence of symptoms. [2,3] Once cancer has grown, it may cause any of the following symptoms, depending on its size and exact location in the large intestine:

  • A persistent change in your bowel habits, which may include diarrhoea (or very frequent bowel movements), constipation, or a change in the consistency of your stool, including narrowing of stools [2,3,4]
  • Blood in or on the stool or bleeding from the rectum (although this may also be due to causes, such as haemorrhoids, or inflammatory bowel disease) [2,3,4]
  • Persistent abdominal discomfort, such as cramps, gas or stomach pain [2,3,4]
  • A feeling that your bowel does not empty completely or incomplete bowel evacuation [2,3,4]
  • Fatigue or weakness [2,4]
  • Unexplained weight loss [2,3,4]
  • Unexplained anaemia (shortage of red blood cells) may lead to fatigue and shortness of breath. [3]

Do not hesitate to make an appointment with your doctor if you notice any persistent changes in your bowel movements, habits, or stool consistency or if you are worried about stomach discomfort or pain. [2]

How is colorectal cancer diagnosed?

If you have any of the signs and symptoms above, your doctor may recommend any combination of the following tests and/or procedures:

  • Colonoscopy: This procedure is done under sedation and makes use of a long, flexible, and slender tube which has a video camera attached to it. This enables your doctor to visually inspect your colon and rectum and to also remove small tissue samples (biopsies) for analysis under a microscope. It is also possible to completely remove small polyps with this procedure. [3,6]
  • Blood tests: While there is no blood test to accurately diagnose colorectal cancer, blood tests are performed to provide information on your overall health, including your kidney and liver function, and also to help determine your prognosis by measuring certain chemicals that are sometimes produced by colorectal cancers (called carcinoembryonic antigen or CEA). [3,6]

If you have been diagnosed with cancer, you may have to go for additional tests to see whether cancer has spread to other organs. This is done to stage your cancer. Staging, which reflects the extent of cancer, is required to determine the most appropriate treatment options. Colorectal cancer can range from stage 0 (localised cancer that is small and that is limited to the lining of the colon or rectum) to stage IV (where the cancer is spread or metastasised to other areas of the body). [6]

Tests to assist with staging include:

  • Ultrasound [3]
  • X-rays [3]
  • Abdominal, pelvic or chest computed tomography (or CT) scans [3,6]
  • Magnetic resonance imaging (MRI) scans or Position Emission Tomography (PET) scans. [3]

How is colorectal cancer treated?

Early-stage colorectal cancer

When cancer is very small or restricted to the wall of the colon/rectum, it may qualify for treatment with minimally invasive treatment options such as:

  • Polypectomy – this is for cancer that is small, localised, and completely contained within a polyp and where the polyp is excised during a colonoscopy (see How is colorectal cancer diagnosed) [6]
  • Endoscopic mucosal resection – this for bigger polyps which are then removed during a colonoscopy with the use of special surgical instruments that not only remove the polyp, but also a small amount of the inner lining of the colon [6]
  • Laparoscopic resection – this is also called key-hole surgery and requires several small incisions in the abdominal wall. This procedure allows the surgeon to visually examine the colon with the help of a video camera that is attached to the laparoscope. It will also provide the surgeon with the opportunity to perform lymph node biopsies, if considered necessary. [6]

Advanced cancer

For cancers that have spread within the colon or that have grown through the colon, treatment options include:

  • Partial colectomy – this is where the section of the colon/rectum that hosts the cancer is removed along with a margin of healthy tissue on either side. It may be possible to reconnect the healthy portions of the colon or rectum. While open surgery may sometimes be required, this procedure can also be performed via laparoscopic surgery. [5]
  • Colostomy – if it is not possible to reconnect the healthy portions of your colon and rectum, the surgeon may have to attach one end of the colon to the abdominal wall. This will create an opening through which stool can be eliminated into a bag that fits tightly over the opening. Colostomies can be temporary or permanent. [6]

If cancer has spread only to your lungs and/or liver and your health is otherwise good, it may still be possible to remove the cancerous lesions with surgery. This is usually followed by chemotherapy to provide you with a chance to be cancer-free over the long term. [3,6]

In addition to the surgical procedures and chemotherapy mentioned, treatment for colorectal cancer may also involve radiation therapy, targeted drug therapy and immunotherapy. Radiation therapy can be utilised to shrink tumours prior to surgery or to relieve symptoms, such as pain, in instances where surgery is not an option. Targeted therapy exploits specific abnormalities present within cancer cells that will lead to cell death. It is usually combined with chemotherapy and is mostly reserved for people with advanced colon cancer. Another treatment option that is usually reserved for patients with advanced colorectal cancer, is immunotherapy. With immunotherapy, medicines are used to stimulate your own immune system to fight cancer cells. Not all colorectal cancers will respond to such treatment. [3,6]

Take-home message

Screening for colorectal cancer allows early detection. Early detection provides the greatest chance for a cure. However, even if colorectal cancer is detected at a later stage, there are several remaining treatment options to may either help to induce remission or to provide the patient with the best quality of life possible. If you notice any persistent changes in your bowel habits, do not hesitate to make an appointment with your doctor for a thorough medical evaluation.


  1. American Cancer Society Medical and Editorial Team; What is Colorectal Cancer?; American Cancer Society; dated 29 Jun 2020; accessed on 01 Feb 2022; available from,to%20grow%20out%20of%20control.
  2. Mayo Clinic Staff; Colon cancer; accessed on 02 Feb 2022; available from
  3. Cleveland Clinic Medical Professional; Colorectal (Colon) Cancer; dated 22 April 2020; accessed on 02 February 2022; available from
  4. CANSA; Colorectal Cancer Leaflet; 2018; accessed on 03 February 2022; available from
  5. American Cancer Society Medical and Editorial Team; Can Colorectal cancer be prevented? Colorectal cancer causes, risk factors and prevention; American Cancer Society; dated 09 Jun 2020; accessed on 01 Feb 2022; available from
  6. Mayo Clinic Staff; Colon cancer – Diagnosis and Treatment; accessed on 02 Feb 2022; available from