Colorectal Cancer

What is colorectal cancer?

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

Colorectal cancer is the most common cancer in Hong Kong and the second leading cause of death.1,2

Stages of colorectal cancer

Colorectal cancer can be described in stages depending on how early or advanced the cancer is. These include:

  • Stage 0 – The cancer is in its earliest stage and has not spread beyond the inner layer (mucosa) of the colon or rectum
  • Stage I – The cancer has been found in the mucosa, and has spread beyond the inner layer of the colon or rectum to the submucosa, but has not spread to the lymph nodes
  • Stage II – The cancer has spread beyond the layer of muscle surrounding the bowel and reached the outermost layers of the colon or rectum and surrounding areas, but has not spread to the lymph nodes
  • Stage III – The cancer has spread to the lymph nodes, but not to distant organs
  • Stage IV – The cancer has spread to distant organs (e.g. lung, liver, peritoneum) throughout the body

Signs and symptoms of colorectal cancer

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

Bright red or dark blood in your stool

Sudden changes in bowel motions

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

Weight loss

Abdominal discomfort or bloating

Unexplained anaemia (low iron)

causing tiredness and breathlessness

A lump or pain around the anus


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)


Treatment for colorectal cancer depends on the type, size and stage of the cancer, and your age, general health and treatment preferences. The mainstay of treatment for colorectal cancer is surgery, which may be provided alongside chemotherapy, radiation therapy or targeted therapies depending on the stage of the disease.


The surgical procedure used to treat colorectal cancer is a colorectal resection (colectomy), which involves the removal of all or part of the colon. The two techniques for a colectomy include:

  • Open colectomy – where the surgeon makes a large incision through the skin and abdominal wall to remove a section of the colon
  • Laparoscopic (keyhole) colectomy – a less invasive procedure that uses three small incisions to access the colon

While both techniques are effective at removing cancer, laparoscopic surgery is now the routine technique used for colorectal resection, providing advantages including reduced blood loss, postoperative pain and wound infection, a faster gastrointestinal and functional recovery from surgery and shorter hospital stay.

Other options include:

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, quantity and degree of cell change (dysplasia) 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


For a full list of references, click here.
  1. Centre for Health Protection. (2019). Colorectal Cancer. Accessed 14 November 2019 at
  2. Healthy HK, Department of Health. (2019). Colorectal Cancer. Accessed 14 November 2019 at
  3. Colorectal Cancer Screening Program Background. (2019). Hong Kong Department of Health. Accessed 29 November 2019 from
  4. What is Colorectal Cancer? Colorectal Cancer Screening Program. (2019). Hong Kong Department of Health. Accessed 29 November 2019 from

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