What Causes Colorectal Cancer?

Colorectal cancer is one of the most common form of cancer internationally, and the number one form of cancer in Singapore for both men and women. In our series of four-part articles, we will be looking at:

Do read on to find out more about one of the greatest threats to your life, and be equipped with the knowledge to prevent it from causing you your life. In this article, we will be discussing about the what causes colorectal cancer.

What is Colorectal Cancer?

Colorectal cancer, as the name suggests, is the cancer that affects the colon as well as the rectum, and is also known as bowel cancer. The colon makes up most of the large intestine and the rectum is the lowest part of the large intestine, connecting it to the anus.

Anatomy of the Large Intestine
Image 1.1: Anatomy of the Large Intestine Source: American Society of Colon and Rectal Surgeons (ASCRS)

This usually begins as small, benign (noncancerous) clumps of cells known as polyps, that form on the inside of the colon. Polyps are very small and only confined to the colon, and they only cause very few symptoms. Hence, they might be easily overlooked if no screening is being conducted.

If the Polyps cells are undetected and not removed from the colon, over time these cells can become colon cancers.  The cancer will develop and spread to other parts of the body, such as neighbouring organs and intestines, and damage them.

Statistics of Colorectal Cancer

According to the World Health Organization (WHO), colorectal cancer is the second most common cancer that causes death in both men and women. For men, colorectal cancer is the third most common cancer, after lung and prostate cancer, while for women, colorectal cancer is the second most common form of cancer, after breast cancer. While it is a problem that plagues both genders equally, men tend to develop it earlier in their lives.

In local Singaporean context, colorectal cancer is the most common cancer in both men and women. The number of people diagnosed with colorectal cancer have been increasing consistently through the years.

Unfortunately, on the world’s stage, Singapore is one of the countries with the highest numbers of colorectal cancer cases in Asia.

However, thanks to advancement in medical technology, the number of deaths has been dropping steadily throughout the last 15 years. Improvements in screening techniques as well as treatments have allowed people to detect colorectal cancer in its early stages, and effectively treat them as soon as possible.

Image 2.1: Various types of screening for colorectal cancer for early detection

Source: https://www.youtube.com/watch?v=mk8lyLWX_OU

Causes & Risk Factors of Colorectal Cancer

While they are no outright causes of colorectal cancer, these are risk factors that exacerbate the chances of getting colorectal cancer.

Colorectal Polyps

As mentioned, Polyps growth in the colon can begin benign, but if left untreated can become cancerous, and even spread to other parts of the body.


Men and women over the age of 50 have a higher risk of developing colorectal cancer. More than 90% of colorectal patients are over the age of 50. However, the rates of colon cancer developing in people under the age of 50 have been increasing in recent years.

History of Cancer

People who were previously diagnosed with colorectal cancer and recovered, or had colorectal polyps detected and removed have a high risk of experiencing a recurrence.

Women who previously had ovarian, uterine or breasts cancer also have a higher risk of developing colorectal cancer.

People who previously suffered from cancer in the abdomen area and have underwent radiation therapy directed at the area also face an increase in the risk of colorectal cancer.

Radiation therapy for cancer
Image 3.1: Radiation therapy for cancer Source: Hell Doktor

Family History of Colorectal Cancer

If you have more than one blood relative who has had colorectal cancer, your risks of getting colorectal cancer is even higher. The chances are even higher if the relative suffered from colorectal cancer at a young age.

Inherited gene mutations 

While only a small percentage of colorectal cancers are due to inherited genes, some mutated gene can greatly increase your risk of colorectal cancer. The most common inherited gene mutations that results in an increase colon cancer risk are Lynch syndrome and familial adenomatous polyposis (FAP). These forms of colorectal cancer are also known as hereditary nonpolyposis colorectal cancer (HNPCC). Some people with a tumor suppressor gene known as Sprouty2 also have an increased  risk of developing certain colorectal cancers.

Inflammatory intestinal conditions

Chronic inflammatory intestinal conditions such as ulcerative colitis, Crohn’s disease and irritable bowel disease (IBD), can increase the risk of developing colon cancer.


One of the most important role in affecting your risks of getting colorectal cancer is actually your diet. Diet that is high in fats and calories, while low in fibre is believed to increase the risk of colorectal cancer. Consuming red meat and processed meat are also associated with increasing the risk of colorectal cancer.


People who are obese or overweight face an increased risk of colorectal cancer and even worse, they have an increased risk of dying of colorectal cancer.

Smoking and Alcohol

People who smoke a lot and consume alcohol in large amounts are also at a higher risk of developing colorectal cancer.

Lack of Physical Activities

Regularly exercising or engaging in some forms of physical activities can help in reducing your risk of colorectal cancer.

Written by: Lim Jun Tian

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