Colorectal Cancer

What is colorectal cancer?

Colorectal cancer occurs when abnormal cells grow uncontrollably in the large bowel or rectum, forming a cancerous tumour.

Most colorectal cancers develop on the inner wall of the colon and rectum and usually start with growths called polyps.

These polyps are benign growths and usually harmless, however they can become cancerous if left undetected.

Colorectal cancer includes colon cancer or rectal cancer, depending on where the cancer is located and the area it originates from. Colorectal cancer is the most common cancer in Hong Kong and the second leading cause of death.1,2

Is colorectal cancer hereditary?

One third of colorectal cancer cases are caused by genetics and family history.3

The three common inherited disorders which have been linked to colorectal cancer are:

  • Hereditary Non-Polyposis Colorectal Cancer (HNPCC) (known as Lynch Syndrome) – results in mutations to the genes that protect cells from growing abnormally and turning into cancerous cells.2
  • MYH – Associated Polyposis (MAP) – caused by a genetic mutation in the gene MYH gene which results in numerous (10-100) polyps (abnormal tissue growth) which can become cancerous.2
  • Familial adenomatous polyposis (FAP) – causes significant numbers (100 – 1000) of adenomatous polyps (gland-like tissue growths) in the lining of the large intestine.2

Stages of colorectal cancer

The TNM system is used to stage colorectal cancer, which helps doctors understand how your cancer spreads. The TNM stands for:

  • Tumour – the degree to which the tumour has affected the inner wall of the colon and other tissue, for example has it grown outside the wall of the rectum or colon? 6
  • Node – is a measure of whether lymph nodes have been affected.
  • Metastasis – the degree to which the cancer has spread to other organs of the body.

Signs and symptoms of colorectal cancer

Not everyone experiences symptoms of colorectal cancer, however some common signs include: 5

Sudden changes in bowel motions

such as diarrhoea, constipation, having narrower stools, or stools that contain mucus

Bright red or dark blood in your stool

A lump or pain around the anus

Weight loss

Unexplained anaemia (low iron)

causing tiredness and breathlessness

Abdominal discomfort or bloating

Diagnosing colorectal cancer

Cancer screening plays an important role in identifying colorectal cancer in people who do have any signs or symptoms. The Hong Kong Colorectal Cancer Screening Program is open to eligible people between 50 and 75 years of age – who will have the opportunity to perform a stool occult blood test to check for any blood particles within the stool (a potential sign of colorectal cancer).3

For people who have symptoms of colorectal cancer or the diagnosis is uncertain, a full examination of the colon is required. The two common tests used for this are:

  • Colonoscopy – A colonoscopy involves inserting a camera on a flexible tube into the rectum to examine the entire large bowel. Most commonly patients with severe iron deficiency anaemia and minimal bowel symptoms are diagnosed through colonoscopy. It can be used for both diagnostic and therapeutic purposes, with the ability to obtain tumour biopsies, stop tumour bleeding and place stenting to relieve obstruction.4
  • CT colonography – CT colonography (or virtual colonoscopy) uses a CT scanner to produce 3D images of the large bowel and rectum, and provides a less invasive option for people who are unable to have a colonoscopy. However, a colonoscopy may still be required if a biopsy needs to be taken.

Further tests

If bowel cancer is diagnosed, further tests are usually carried out to see if the cancer has spread beyond the colon or rectum.

These tests can include:

  • Computed tomography scan (CT scan)
  • Magnetic resonance imaging (MRI)
  • Positron emission tomography (PET scan)


Frequently asked questions

What causes colorectal cancer?

Certain risk factors can play a role in the development of colorectal cancer. These include:

  • Age – People aged 50 or above are more likely to develop colorectal cancer
  • Diet – Diets with high animal fat, high protein and low fibre may increase the risk of colorectal polyps or colorectal cancer
  • Family history – A person who has one or more family members with colorectal cancer may have a higher risk of developing the disease
  • Colorectal polyps – Size and quantity of polyps can increase the risk of colorectal cancer
  • Smoking
  • Colorectal disease history – previously having diseases such as Crohn’s disease or ulcerative colitis significantly increases your risk
What can I do to decrease my risk of colorectal cancer?

Things you can do to reduce your risk of getting bowel cancer include:10

  • Exercising regularly and maintaining a healthy weight
  • Limiting your alcohol intake
  • Eating a healthy and balanced diet, which is low fat, rich in wholegrains and fibre
  • Regular screening for colorectal cancer.


How do you know if it’s colorectal cancer or haemorrhoids (piles)?

Haemorrhoids, or piles, are soft lumps of enlarged blood vessels around and inside the anus. They usually result from a sudden increase in pressure – such as during pregnancy, constipation or heavy weight lifting.

Symptoms of haemorrhoids include: 4

  • Painful bowel motions
  • Bright red blood on toilet tissue, or in the stool
  • Extreme itching around the anal area
  • A lump or swelling around the anus.

Since the symptoms of haemorrhoids and colorectal cancer can be similar, you should talk to your doctor if you are experiencing these symptoms. 4


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