Cancer is characterised by the development of abnormal cells that destroy normal body tissue, and colorectal cancer is cancer of the bowel.

The bowel is divided into two parts, the small and large bowel. Most cancers develop in the large bowel, i.e. the colon and rectum.

- There were 4,979 new colorectal cancer cases in 2014.
- Among these cases, colon cancer and rectum cancer account for 3,058 and 1,921 cases respectivel
- Colorectal cancer is the most common cancer in Hong Kong, and the second leading cause of cancer deaths following lung cancer
- 2,034 deaths resulted from colorectal cancer in 2014
   
  Source: Hong Kong Cancer Registry, Hospital Authority
In most cases, the cause of colorectal cancer is still unknown. However, we know that some factors are associated with an increased risk of developing colorectal cancer:

Age: The risk of colorectal cancer increases with age. Most cases occur in people over 50.
Diet: There is evidence to suggest that colorectal cancer may be linked to our diet. It is thought that a diet high in animal fat, and low in fibre, may increase the risk of developing colorectal cancer.
Other environmental factors: Lack of physical exercise, obesity, smoking and heavy alcohol consumption are all associated with an increased risk of developing the disease.
Family history of bowel cancer: If you have first-degree relatives with colorectal cancer, you have an increased risk of developing the disease.
Personal history of bowel polyps or colorectal cancer: If you have previously developed bowel polyps or colorectal cancer, even if these were already removed, your risk of developing the disease again is higher.
Inherited diseases: Two inherited diseases, known as Familial Adenomatous Polyposis (FAP) and Hereditary Nonpolyposis Colorectal Cancer (HNPCC) Syndromes, cause around 1% and 4% of colorectal cancer cases, respectively. These are inherited in an autosomal dominant pattern. Patients with FAP will develop hundreds of benign polyps in the colon that eventually progress to cancer. HNPCC is characterised by the development of colorectal cancer at an early stage, and in more than one family member.
While early stage colorectal cancer may often have no symptoms, the following can sometimes occur:

- Blood or mucus noticed in the bowel motion or toilet bowl
- Changes in bowel habits lasting more than 2 weeks, such as alternating diarrhoea, constipation, narrowing of the stool (thin like a pencil), or a persistent feeling of incomplete emptying after a bowel movement
- General abdominal discomfort (gas pain, bloating, fullness or cramps)
- Unexplained weight loss

According to a survey conducted by the Hong Kong Cancer Fund, the general public is not aware of colorectal cancer, nor do they seek medical help when experiencing abnormal bowel conditions. For example, many people ignore blood in the stool, which can be a symptom of colorectal cancer. Cancers are often in their late stages when symptoms like this appear, causing a delay in treatment due to lack of awareness and a late diagnosis.

When you see blood in your bowel motion, do not assume that this is caused by haemorrhoids (piles). Check with your doctor immediately.
- Colorectal cancer is most common among people over 50
- It is also more common among people with a family history of colorectal cancer or colorectal polyps.
- Chemotherapy
 

Chemotherapy (chemo, for short) is the use of drugs with toxic components to kill cancer cells. Cancer cells divide faster than normal cells. This gives chemo drugs a chance to target them. They are usually injected into the bloodstream and kill cancer cells when circulated through the body.  

Fluorouracil (5-FU), Oxaliplatin, Irinotecan and Capecitabine are some of the drugs used to treat colorectal cancer. Fluorouracil is more commonly used, sometimes together with other chemo drugs like folinic acid to enhance treatment. Before deciding on a drug combination, ask your doctor to compare its potency and side effects with other possible choices. 

Chemotherapy can also be used after surgery to reduce the risk of cancer recurring. In adjuvant treatment, (chemo following surgery to remove tumours) if cancer cells are found in nearby lymph nodes or assessment indicates that there is a risk of cancer returning, you may be given chemotherapy as a follow-up treatment. 

Colorectal cancer can often be cured if found early. In a small number of cases where cancer has spread, cancer cells are mostly found in the lung or liver. It is more difficult to expect a full recovery when colorectal cancer has already spread (metastatic), but chemotherapy can be used to reduce symptoms and stablise the condition. 

Your doctor will suggest the best chemo combination according to your physical condition, treatment progress and reaction to side effects. Those with metastatic colorectal cancer are unlikely to consider surgery an option.

- Targeted Therapy
 

Using drugs made in a bio science lab to kill cancer cells is known as biologic therapy. There tend to be less side effects when compared with traditional chemotherapy, offering hope to those with late-stage cancers. As a relatively new treatment, targeted therapy does not cure metastatic colorectal cancer at present, although it may enhance treatment effects and prolong life.

Targeted therapy drugs used to treat colorectal cancer include:
1. Cetuximab; 2. Panitumumab; 3. Bevacizumab; 4. Aflibercept; 5. Regorafenib.
Drugs 1 and 2, known as EGFR inhibitors in the bio-medical industry, kill cancer cells by blocking the information necessary for their division and proliferation. They only work for people whose KRAS and NRAS genes have undergone mutation. So tests must be done before prescribing these drugs. Drugs 3, 4 and 5 are anti-angiogenesis or angiogenesis inhibitors which make it hard for cancer cells to grow blood vessels by starving them of nutrition.

- Radiotherapy
 

High-energy rays are used to bombard cancer cells in radiotherapy. Compared to chemotherapy which covers the entire body, radiotherapy is a local treatment targeting only the cancerous area. Since other parts of the body receive no radiation, side effects hopefully can be controlled more easily.

For colorectal cancers, radiotherapy is applied to the rectum area more often than the colon. Specifically, radiotherapy usually follows surgery as adjuvant treatment to help clear the tumour area of residual cancer cells. 

For rectum cancers which are either advanced or difficult to remove with surgery, radiotherapy can be first used to reduce the size of the tumour to facilitate surgery, or achieve better control of the situation.

For rectum cancers with a high risk of recurrence, radiotherapy may also be used after surgery. If the physical condition of the person permits, chemotherapy can be added, hopefully to enhance the effect of radiotherapy. However, a combination of chemo and radiotherapy can also cause more side effects.

Recurring cancers as a rule are difficult to cure. But radiotherapy can be used to shrink the tumour and relieve pain, especially when cancer cells have spread to the bone.

Radiotherapy is usually administered using large instruments similar to an X-ray machine in hospital and treatment centres. Successful treatment requires detailed planning beforehand. One must ensure that the high-energy beam aims at the tumour and avoids normal cells, with the right intensity (similar to medication dosage) to kill the largest number of cancer cells, while causing minimal harm to normal tissue.

The planning process involves many steps. The tumour area will be scanned with an X-ray or CT scanner to ascertain its exact location, size and shape. A mark will be drawn on the skin as the 'target' where the beam enters the body. A mould will be custom-made to best fit the body and help guide the beam.

A radiotherapy session is similar to an X-ray, but takes slightly longer. Anaesthesia is not necessary. You lie on the platform bed in the machine room, while the radiologist monitors your progress next door. You will be able to communicate with the radiologist when necessary. Once the machine is turned on emitting the beam, it is important to lie still, as even a slight movement may cause the beam to fall on normal tissues. Each beam treatment only takes a few minutes, and like an X-ray, you will not feel anything.

For further details on treatment of colorectal cancer, please download our cancer information booklet here or call Our CancerLink Hotline: 3656 0800.