Colorectal Cancer – Symptoms, Treatment & Prevention in Singapore

 In Cancer Care Guide, Cancer Types

Table of Contents

Colorectal cancer consists of colon cancer and rectal cancer, which as their names suggest, are cancer of the colon (ie., the large intestine) and the rectum respectively. They are often grouped together because of their similar features. 

Together, colon and rectal cancers are among the most common cancer types globally as well as in Singapore. According to Singapore Cancer Registry Report, colorectal cancer is: 

  • The most common cancer among Singaporean males, accounting for 1 in 6 cancer diagnoses among males.
  • The second most common cancer among Singaporean females, accounting for 1 in 7 cancer diagnoses among females.

In addition to its prevalence, colorectal cancer poses a health challenge because many cases are diagnosed only at advanced stages, when treatment is less effective. 

In this article, we will cover the important aspects of colorectal cancer, including causes and risk factors, symptoms, diagnosis and treatments of this condition. We will also explain why colorectal cancer is difficult to detect at early stages, and what you can do about it. 

Causes of colorectal cancer

Generally, cancer occurs when the cells undergo a genetic mutation that drives them to multiply uncontrollably. In colorectal cancer, the process is believed to be similar. Cells in the lining of the colon or rectum develop in an unregulated manner, forming tumours. Benign or non-cancerous tumours are known as polyps. They do not invade other cells. Malignant or cancerous tumours can spread through the bloodstream to other tissues and organs. Some types of polyps start out as benign and become cancerous over time.    

Most polyps detected early are benign and can be safely removed. In the event a polyp is cancerous, early detection still facilitates better therapeutic outcomes, as cancer at this stage is unlikely to have spread to other tissues. Unfortunately, when cancer has progressed and metastasized, treatment success rate drops significantly.

The exact cause of the genetic mutation that causes colorectal cancer is still unknown. However, over the years, researchers have identified a number of risk factors that can increase an individual’s chance of developing colorectal cancer. We will go over them in the next section.

The risk factors of colorectal cancer

The risk of getting colorectal cancer increases with age, with most diagnosis made after the age of 50. However, there has been an uptick in the number of younger patients diagnosed in their 40s, 30s, and even 20s. In Singapore, approximately one in 10 colorectal cancer cases occur in patients under 50 years old as of now. Understanding risk factors of the disease other than age therefore becomes important for prevention and early detection of the disease. 

They include: 

  • Having a family history of colorectal cancer or colorectal polyps: Consulting a genetic counsellor may be helpful in assessing your risk in such cases. Genetic testing can also reveal if you have hereditary polyp disorders which have a high chance of developing into malignant polyps, typically at a younger age. These disorders include Lynch symdrome, familial adenomatous polyposis (FAP), MUTYH-associated polyposis (MAP). 
  • Long-time diagnosis of inflammatory bowel diseases (IBD) such as ulcerative colitis or Crohn’s disease. Research shows that the extent and severity of IBD also influences the likelihood of developing colorectal cancer. 
  • Having polyps in the colon or rectum: A type of polyp called adenomas is known to have the potential to become cancer. The best way to know for sure if a polyp is present is through a colonoscopy. If a polyp is found, it is typically removed or sampled (biopsy) and sent for analysis in the laboratory.

A number of lifestyle risk factors have been linked to colorectal cancer. The good news is these are modifiable, ie., we can make changes to our lifestyle habits to lower the risk. They include: 

  • Obesity or overweight 
  • Smoking
  • Sedentary lifestyle 
  • A diet that is high in animal protein, saturated fats and low in fiber
  • Excessive alcohol consumption 

Of note, in Singapore, men have a slightly higher risk of colon and rectal cancer than women. Chinese Singaporeans are found to have a mildly elevated risk of this cancer compared to other ethnic groups. 

Signs and symptoms of colorectal cancer

The signs and symptoms of colorectal cancer vary from one individual to another. They are also highly non-specific, ie., they can be present in other diseases, especially during the early stages. This poses a challenge for patients to report the symptoms to doctors and for doctors to diagnose this condition. 

Below are the common symptoms a colorectal cancer patient may experience: 

  • Changes in bowel habits, such as constipation, diarrhoea or loose stool
  • Feeling the bowel is not empty after passing motion 
  • Rectal bleeding, or the sight of bright, red blood coming from the rectum
  • Dark or black colour stools, which indicates the presence of blood in the feces
  • Unexplained pain and cramp in the abdomen area
  • Unexplained weight loss
  • Low energy and fatigue
  • Iron deficiency anemia, due to loss of blood, which is often discovered with a blood test. 

If you experience one or a few of these symptoms for more than a few weeks, it is a good idea to visit a doctor to find out what causes the symptoms. For instance, a person with a history of piles (haemorrhage) may think the rectal bleeding is due to a recurrence. But if symptoms worsens or do not improve with the usual treatment for piles after two weeks or more, a visit to the doctor for further evaluation is recommended.  

Some of the signs and symptoms of colorectal cancer overlap with those of stomach cancer. However, there are differences, such the location of abdominal pain. Pain the upper part of the abdomen is more likely to stem from the stomach, while pain in the lower abdomen is likely to come from the colons. Learn more from our guide to stomach cancer here.

Signs and Symptoms of Colorectal Cancer

The staging of colorectal cancer

The staging of colorectal cancer is important to help doctors determine the best treatment approach and predict the prognosis.

The stages of colorectal cancer are generally described as:

Stage 0 – this is the earliest stage when cancer has not yet penetrated the basal membrane of the tissue. This stage is referred to as carcinoma in situ.

Stage 1 – cancer has penetrated the basal membrane of the bowel but not spread beyond the wall of the rectum or colon.

Stage 2 – cancer has broken through the wall of the colon or rectum but has not reached nearby lymph nodes.

Stage 3 – cancer has spread to nearby lymph nodes but has not reached other organs.

Stage 4 – cancer has spread to other organs, such as the liver, lungs, ovaries, peritoneum.

Diagnosis of colorectal cancer

Colonoscopy is one of the key tests in diagnosing, as well as screening for, colorectal cancer. It allows the doctor to insert a thin flexible tube-like device to look inside the colon and rectum and examine for any abnormalities. The procedure itself causes little, if any, discomfort, as it is often conducted under sedation. However, it requires bowel preparation, which involves a low fiber diet for 2-3 days, and taking laxatives to cleanse the bowel prior to the procedure. 

If any abnormality is discovered during the colonoscopy, the doctor will use the tip of the colonoscope to remove a sample of the abnormal cells – a process known as biopsy. If a polyp is found and can be removed, polypectomy (i.e., removal of polyp) will be conducted. Tissue samples from the polyp or biopsy are then sent for laboratory tests to confirm the nature of the mass. Test results will help doctors conclude the diagnosis and recommend the next course of action.

Apart from colonoscopy, a number of other tests are available in the doctor’s toolkit. Depending on the patient’s symptoms and profiles, different diagnostic tests may be ordered, including: 

  • CT Scan or MRI Scan, often to check if colorectal cancer has spread to other organs
  • Ultrasound, commonly used to check the status of rectal cancer
  • Blood test, often to look for indication of anemia – which is one of the symptoms of colorectal cancer – through red blood cell (RBC) count, or inditcation of other cancers, through tumour markers.
  • Biomarker tests – These tests help doctors identify specific characteristics of the tumours and determine treatment options, such as whether the cancer is caused by certain genes, or if immunotherapy may potentially benefit the patient.

Treatment of colorectal cancer

Colorectal cancer is highly treatable if detected at an early stage. Depending on the type and stage of cancer confirmed through diagnostic tests, patient’s health condition and care goals, recommendations for treatment plans may be tailored accordingly. Below is an overview of the available treatment options, which include:

  • Surgery 
  • Chemotherapy, targeted therapy and immunotherapy
  • Radiotherapy

Surgery for colorectal cancer

Surgery is an indispensable tool in the treatment of this disease. It aims to remove the malignant tumour and the nearby lymph nodes to reduce the risk of cancer spreading to other tissues or organs (ie., metastasis). In early detected colorectal cancer cases, surgery can be the most effective treatment option. In advanced cases, it may be recommended as part of palliative care to reduce severity of pain and other symptoms for the patient.


Chemotherapy aims to destroy cancerous cells by using pharmacological drugs. It may be recommended before the surgery, to shrink the tumour before surgically removing it – this is called neoadjuvant therapy. It may also be applied after the surgery to eliminate the remaining cancer cells, this is called adjuvant treatment. 

Recently, scientists developed new drugs that target specific proteins, genes or other factors which are responsible for promoting cancer growth. These drugs are known as targeted therapy. They often have fewer side effects compared to conventional chemotherapy. However, they may not be suitable for all patients. Examples include:

  • Bevacizumab (Avastin) 
  • Ramucirumab (Cyramza)

Another class of drugs aims to boost the body’s immune system function to fight cancer cells. This is known as immunotherapy. Checkpoint inhibitor is one of the important types of immunotherapy used in treating colorectal cancer.

Radiation therapy

Radiation therapy is the use of high-energy radiation beams to disintegrate the tumour. Similar to chemotherapy, radiation therapy may be beneficial before the surgery to shrink the tumour, or after the surgery to prevent recurrence at the location where cancer started. It may be given together with chemotherapy to increase effectiveness and reduce scarring at the radiation site. This technique is referred to as chemoradiation therapy

Prevention and screening of colorectal cancer

Lifestyle habits to reduce the risk of colorectal cancer

The most effective way to prevent colorectal cancer is to manage the risk factors that are in our control. This means making healthy lifestyle choices to lower the risk. Consider the following:  

  • Quit or avoid smoking: Since smoking is a risk factor for many health conditions, this helps to lower the risk for more than just colon and rectal cancer.
  • Limit alcohol consumption
  • Be more active
  • Lose weight if you are overweight or obese
  • Maintain a healthy diet with sufficient fiber, fresh fruit, vegetables and whole grains while reducing consumption of saturated fat and processed, deep-fried or chargrilled meat.

Screening for colorectal cancer

Screening is another important measure to prevent and detect colorectal cancer early, which can improve treatment outcome significantly. Screening can help to detect precancerous changes, such as an adenomatous polyp at an early stage, practically preventing the development of cancer. 

For adults with average risk, the standard recommendation is to start screening from the age of 50. A number of tests are available: 

  • The Faecal Immunochemical Test (FIT) to be done at home: this non-invasive test helps to detect the presence of blood in the stool. Under The National Health Screening Program, eligible Singaporeans and SPR above 50 years old can collect a FIT test kit for at Singapore Cancer Society or at partnering collection points, collect stool samples at home and follow instructions to send the sample back to SCS, all for free. Results will be informed to you personally. FIT should be repeated every year.
  • Colonoscopy: this is an intensive screening exercise, recommended to be done every 5 to 10 years (see details in Diagnosis section below)
  • Blood test for colorectal cancer screening: Epi proColon is the first and only FDA-approved blood test to screen for colorectal cancer, for people who are unwilling or unable to be screened by the above methods. Do contact your oncologist to enquire about it.

Individuals with a high risk profile are recommended not to wait until the age of 50 to seek medical consultation and/or to go for colorectal cancer screening. Early detection can save lives. Depending on which risk factor you identify yourself with, you may opt for genetic counselling, visiting a gastroenterologist (a doctor specialising in gastrointestinal tract diseases) or a medical oncologist for advice and screening. 

Takeaway message

Colorectal cancer is the commonest cancer type, and one of the top causes of cancer deaths in Singapore. However, if detected early, the disease is highly treatable. Early detection involves understanding personal risk factors, noticing early signs and symptoms and promptly seeking medical advice, as well as regular screening. 

By sharing knowledge about the primary aspects of colorectal cancer, we hope to empower you to take control of your health and protect yourself and loved ones against the disease. 

Dr Donald Poon

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