Colorectal cancer develops along the inner lining of colon or rectum and is the most common cancer in Singapore. It is the top cancer for men, and second only to breast cancer for women. Singaporean Chinese males are at most risk as they have one of the highest age-standardised incidences of rectal cancer in the world.

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10 most common cancers affecting men & women (2014 – 2018)

Men	No. of cases	Women Sponsored Content	No. of cases
Colon & rectum	6,129	Breast	11,232
Prostate	5,368	Colon & rectum	5,109
Lung	5,083	Lung	2,862
Liver	2,758	Corpus uteri (uterus)	2,769
Lymphoid neoplasms	2,358	Ovary & fallopian tube	1,897
Non-melanoma skin	1,975	Lymphoid neoplasms	1,809
Stomach	1,605	Non-melanoma skin	1,568
Kidney	1,494	Thyroid	1,483
Myeloid neoplasms	1,232	Stomach	1,160
Pancreas	1,119	Cervix uteri	1,088

(Source: Singapore Cancer Registry Annual Report 2018: Singapore Cancer Registry 50th Anniversary Monograph 1968-2017)

The most effective way to prevent colorectal cancer is through screening.

How colorectal cancer progresses

Colorectal cancer most commonly tends to arise from pre-existing polyps (small growths along the lining of the colon). Polyps may be present in up to 25% of people aged 50, and they become more common with age.

While these polyps are largely asymptomatic, they can undergo genetic mutations over a period of five to 10 years, and become cancerous. Screening helps to pick up polyps so they can be removed before becoming cancer.

When cancer does develop, it starts in the innermost layer of the colon (the epithelium) before breaking out and spreading to the other layers of the bowel wall. The cancer cells can grow into blood and lymph vessels, and travel (a process known as metastasis) to other parts of the body.

Colorectal cancer starts in the epithelium and grows outwards.
Image: American Cancer Society

Stages of colorectal cancer

After a diagnosis has been made, doctors determine the best treatment options and calculate survival statistics by categorising the spread of cancer in stages. The higher the stage, the more serious the cancer. However, colorectal cancer is highly curable if caught early.

Stages:
Stage 0: The abnormal cells are confined to the epithelium.
Stage 1: The cancer has invaded through the epithelium into the bowel wall.
Stage 2: Cancer has penetrated the outer layer of the colon or rectum.
Stage 3: The cancer has spread to surrounding lymph nodes.
Stage 4: The cancer has metastasised to other organs such as the liver or lungs.

Surgery is the first line of treatment for colorectal cancer. In the earliest stages, surgery alone can offer high cure rates. The cancer is removed with the surrounding lymph nodes and sent for further examination to confirm the stage of the disease. In most cases, the intestines can be reconnected and normal bowel function is restored.

Other treatment options include radiation therapy which uses X-rays to kill cancer cells. Radiation is often used for treatment of rectal cancer and can be given prior to surgery to shrink a tumour, or after surgery to reduce the risk of local recurrence.

Chemotherapy involves taking drugs that are ingested by mouth or injected into the bloodstream to destroy tumour cells that have spread to other parts of the body. They hinder the growth of cancer but can have unpleasant side effects. Nevertheless, chemotherapy helps patients with incurable cancer to live longer.

Other treatments for advanced cancer include:

1. Targeted therapy – using drugs that suppress cancer cells by modulating growth factors.
   
2. Immunotherapy, which stimulates or enhances the body’s immune system to fight and destroy cancer cells.

This article has been fact-checked by Dr Denis Cheong, colorectal surgery specialist of Surgi-TEN Specialists at Farrer Park Hospital.