Colorectal Cancer

Colorectal cancer is the abnormal and uncontrolled growth of cells in the colon or rectum. Depending on where the cancer starts, it can be called colon cancer or rectal cancer. However, these cancers share many common features. There are 5 parts to the large intestine – the ascending, transverse, descending and sigmoid colon, and the rectum. Colorectal cancer can develop in any of these sections.

Colorectal cancers typically begin as polyps. These are growths on the inner lining of the large intestine. These polyps begin as being non-cancerous, but some may develop into cancer over many years, whereas others may not.

There are 2 main types of polyps – adenomatous polyps (adenomas) and hyperplastic/inflammatory polyps. Adenomatous polyps can sometimes change into cancer, and therefore having an adematous polyp is considered a pre-cancerous condition.

Hyperplastic/inflammatory polyps are more common than adenomatous polyps, but they are generally not pre-cancerous.

In Singapore, colorectal cancer is the most common cancer in men (1 in 6 of male cancer patients), and is the 2nd leading cause of cancer deaths in men. In women, it is the 2nd most common cancer (1 in 7 of female cancer patients), and is the 3rd leading cause of cancer deaths in women.

Adenocarcinomas make up the majority of colorectal cancers. This type of cancer begins in the cells that produce mucus in the large intestine. There are other subtypes of cancers under this type of cancer, and they may result in different prognoses.

Other less common types of colorectal cancers include:

• Carcinoid tumours
• Gastrointestinal stromal tumours
• Lymphomas
• Sarcomas

If cells in the polyp become cancerous, it can invade into the wall of the colon or rectum over time. This wall is comprised of multiple layers, and the cancer spreads from the innermost layer towards the outer layers.

The wall of the large intestine also contains blood vessels or lymph vessels. If the cancer reaches the blood or lymphatic supply, it may be able to travel to the nearby lymph nodes, or to other parts of the body.

While colon cancer can be diagnosed at any age, most patients with colon cancer are over the age of 50. Other risk factors include:

• Having a blood relative who has colon cancer
• Having a personal history of colorectal cancer or polyps
• Having an inherited syndrome such as familial adenomatous polyposis (FAP) or non-polyposis colorectal cancer (Lynch Syndrome)*
• Inflammatory conditions affecting the large intestine – such as ulcerative colitis or Crohn’s disease
• Low fibre, high-fat diet
• Diabetes
• Obesity
• Smoking
• Alcohol use
• Sedentary lifestyle

To help prevent colorectal cancer and other diseases, it is always important to take steps towards living a healthier lifestyle. Such steps include eating more fruits, vegetables and wholegrains which are high in fibre and rich in antioxidants, limiting the amount of fat from animal sources such as red meat, limiting alcohol intake, quitting smoking and staying physically active.

*Inherited syndromes can cause individuals to develop cancers through mutations in their genes, which cause or allow the uncontrolled growth of cells.

In FAP, the mutations in the patient’s genes cause hundreds or thousands of polyps to develop in his/her colon and rectum. This often starts at 10 to 12 years. As there are many more polyps in the patient’s large intestine, there is a higher chance that one or more of these polyps will become cancerous, as early as the age of 20. By 40, most people with FAP will develop colon cancer if the colon has not been removed to prevent it.

In Lynch syndrome, the mutation to the patient’s MLH1 or MSH2 gene causes damage to the DNA repair mechanism. This allows cells to grow abnormally and out of control. The risk of colorectal cancer in patients with this condition can be as high as 80% depending on which gene is affected. Women with Lynch syndrome also face a higher risk of developing endometrial cancer, ovarian cancer, and other types of cancer.

If you are above the age of 50 years old, your doctor will recommend for you to start screening for colorectal cancer.

Faecal Immunochemical Test (FIT) is the screening test that is recommended for the general population who are asymptomatic and do not have a family history of colorectal cancer. FIT involves collecting stool samples using a kit your doctor gives to you. This should be done once a year.

Colonoscopy is another recommended screening test for individuals of the general population who are over 50 years old. This involves using a flexible tube known as a colonoscope to look at the inner lining of the colon and rectum. This is done in the hospital by a trained doctor, and takes about 20 to 30 minutes. A colonscopy should be done once every 10 years.

Those who are at increased risk for colorectal cancer are those who have:

• A first degree relative who had colorectal cancer (it is important to let your doctor know at what age your relative had colorectal cancer)
• Personal history of colorectal polyps
• Personal history of colorectal cancer
• Personal history of ovarian or endometrial cancer
• Have a first degree relative of familial adenomatous polyposis (FAP)
• Inflammatory bowel disease

Please let your doctor know if you have any of the above listed conditions. These affect your risk profile for colorectal cancer, and your doctor may suggest other screenings of different time intervals.

Your doctor may recommend a test to check the stool for blood, which may be a sign of cancer. The tests, which may be a faecal occult blood test (FOBT) or FIT, are done at home. It involves the collection of 1 to 3 samples of stool. If you have already had an abnormal test, let your doctor know as a colonoscopy should be done instead.

Blood tests may also be useful to find certain cancer markers. These chemicals may be produced by colon cancers. These include a chemical called the carcinoembryonic antigen (CEA), and CA 19-9. Raised levels of these chemicals may suggest colorectal cancer, but cannot be used to diagnose cancer.

If your doctor suspects that you may have colon cancer, he/she may recommend a colonoscopy to examine the inside of your colon. This is also used for screening, and it involves the use of a camera attached to a long, flexible tube. This is used to view the inside of the colon and to find any abnormalities. If any areas are considered suspicious, a biopsy can be conducted during the colonoscopy. This involves taking a tissue sample for analysis under the microscope. Your doctor will also be able to remove polyps for examination during the colonoscopy.

Computerised tomography (CT) scans of the abdomen, pelvis and chest will help your doctor to stage the cancer, which is to see the extent of the cancer, and if it i has spread. Rectal cancers will also require an MRI of the pelvics to complete staging.

Treatment depends on the location of the cancer, its stage, the age as well as general health of the patient. It usually involves surgery to remove the cancer, but other treatments may also be recommended based on the stage of the cancer.

If the colorectal cancer is in its early stages and localised, sometimes the removal of polyps may be sufficient to remove the cancer completely. In more advanced stages of colorectal cancer, it may involve the removal of part of the colon, which is known as a colectomy. It is important to consult your doctor in order to understand the best treatment plan for you.

Other treatments that are available, or that may be used in combination include:

• Chemotherapy
• Radiation therapy
• Targeted drug therapy
• Immunotherapy

Locally advanced rectal cancers are often treated with a combination of radiation therapy and chemotherapy prior to surgery improve the chances of a successful surgery.

Once the diagnosis is made, a consultation with an oncologist is essential in order to understand which treatment options are the most suitable.