Why Colorectal Cancer Screening Matters, Even If You Feel Healthy

Colorectal cancer refers to cancers that originate in the colon or rectum. It is currently the most common cancer among men and the second most common cancer among women in Singapore, after breast cancer.

While it is more frequently diagnosed in older adults, there is growing concern both globally and locally about a rise in early-onset colorectal cancer (diagnosed in people under the age of 50), challenging the long-held perception that it is primarily a disease of older individuals.

One of the key challenges with colorectal cancer is that it often develops silently. By the time symptoms appear, the disease may already be at a more advanced stage.

This makes screening especially important, even if you feel healthy. Gastroenterologist Dr Amitabh Monga explains how screening can aid in colorectal cancer prevention and management, the tests involved, and more.

Can colorectal cancer be prevented?

Colorectal cancer cannot always be prevented, but screening can significantly reduce the risk by detecting and removing precancerous changes early.

Most colorectal cancers develop over time from small, benign growths called polyps that form in the lining of the colon or rectum. In many cases, these polyps remain harmless. However, some may gradually become cancerous if left undetected.

During a colonoscopy, these polyps can often be identified and removed in the same procedure. This not only allows for early detection but can also help prevent colorectal cancer from developing in the first place.

What are the warning signs of colorectal cancer?

Being slow-growing, symptoms do not always show up in the early stages of the disease. In fact, it is often only late in the course of colorectal cancer, that patients begin to notice symptoms, such as:

• Changes in bowel habits, such as persistent diarrhoea or constipation
• Blood in stools
• A feeling that the bowel does not empty completely
• Persistent abdominal discomfort, cramps, bloating or pain
• Unexplained weight loss
• Unusual tiredness or symptoms of anaemia

These symptoms may also occur with other conditions such as haemorrhoids (piles), inflammatory bowel disease, or other digestive problems. However, persistent symptoms should always be assessed by a doctor.

Who is at risk of colorectal cancer?

Colorectal cancer can affect anyone, including younger adults.

You may have a higher risk if you:

• Are aged 45 or older
• Have a family history of colorectal cancer or polyps
• Have previously had colorectal polyps detected
• Have inflammatory bowel diseases such as Crohn’s disease or ulcerative colitis
• Smoke excessively
• Drink excessive amounts of alcohol
• Have a diet high in processed meats and low in fibre
• Are overweight or obese
• Have a sedentary lifestyle

What is leading to the rise of colorectal cancer among younger adults?

The rise of colorectal cancer among people under the age of 50 is thought to be linked to a combination of factors, including changes in diet and lifestyle patterns (such as lower fibre intake, higher consumption of processed foods, and more sedentary habits), as well as potential shifts in gut microbiome and other environmental influences that are still being studied.

When should you start colorectal cancer screening?

While colorectal cancer in younger adults is receiving increasing attention, most cases still occur in older individuals. Clinical decisions around screening need to balance individual risk factors and overall population needs.

Routine colorectal cancer screening in Singapore is generally recommended for individuals from around age 45, unless younger individuals have specific risk factors, such as:

• A family history of colorectal cancer or advanced polyps
• A history of inflammatory bowel disease such as Crohn’s disease or ulcerative colitis
• Persistent or unexplained symptoms such as blood in the stool, changes in bowel habits, or unexplained weight loss

What are the different colorectal cancer screening options?

There are several screening methods available. Your doctor can advise the most suitable option based on your age, risk factors, and medical history.

Faecal Immunochemical Test (FIT) / Occult Blood Immunological Test (OBI)

The FIT, also known as an occult blood immunological (OBI) test, checks for tiny amounts of blood in stool that cannot be seen with the naked eye.

The test is usually done at home by collecting stool samples, which are then sent for laboratory testing.

Advantages:

• Non-invasive
• Convenient
• Does not require bowel preparation

If the result from a FIT test is positive, a colonoscopy is usually required to determine the cause.

Virtual colonoscopy

A virtual colonoscopy uses computed tomography (CT) imaging to create pictures of the colon.

Before the scan, patients need to drink a bowel preparation medication to clear the colon. The images are then reviewed by a radiologist.

While it avoids inserting a camera into the colon, it has limitations:

• Small polyps may be missed
• It involves radiation exposure
• If polyps are found, a traditional colonoscopy is still needed for removal

Colonoscopy

This is considered the recognised standard for colorectal cancer screening.

During the procedure, a thin flexible tube with a camera is gently passed through the rectum to examine the entire colon.

If polyps are found, they can usually be removed during the same procedure and sent for testing.

A colonoscopy:

• Allows direct examination of the colon lining
• Detects both cancer and precancerous polyps
• Can prevent cancer by removing polyps early

Most colonoscopies are performed as day procedures, with sedation to improve comfort.

FIT test vs colonoscopy: What is the difference?

Both tests play a role in colorectal cancer screening. Your doctor can recommend the best option based on your health profile.

What happens during a colonoscopy?

How should I prepare?

Before a colonoscopy, you will usually need to:

• Fast for a period of time before the procedure
• Take bowel-cleansing medication to clear the colon

A clean colon allows the doctor to examine the lining carefully and reduces the chance of missing polyps.

What happens during the procedure?

During the procedure, a colonoscope is inserted into the rectum and guided through the colon.

Sedation is commonly used, and the procedure usually takes around 20 to 30 minutes.

If polyps are found, they may be removed immediately.

What happens after a colonoscopy?

Most patients recover from sedation within 30 to 60 minutes.

Some may experience temporary bloating or mild abdominal discomfort due to air introduced during the procedure.

Your doctor will discuss the findings and advise on the next steps.

Are there risks with a colonoscopy?

Colonoscopy is generally a safe procedure when performed by trained specialists.

Possible risks, such as bleeding or injury to the colon, are uncommon. The risk may depend on factors such as whether polyps are removed and the complexity of the procedure.

Seek medical advice after a colonoscopy if you experience:

• Persistent abdominal pain
• Fever
• Ongoing bleeding
• Increasing bloating or discomfort

How often should colonoscopies be done?

The recommended screening interval depends on:

• Your age
• Family history
• Previous colonoscopy findings
• Presence of polyps
• Other medical conditions

Your doctor will be best placed to advise on screening intervals. In most cases, individuals identified as being 'high-risk' may need to be screened every 2 – 3 years. For those with no history of colorectal cancer, and whose previous colonoscopy was clear, screening intervals can be far longer.

How can colorectal cancer risk be reduced?

While no lifestyle change can guarantee prevention, healthy habits may help reduce your risk.

These include:

• Eating more fibre from fruits, vegetables and whole grains
• Limiting processed meats and excessive intake of red meat
• Exercising regularly
• Maintaining a healthy body weight
• Avoiding smoking
• Limiting alcohol intake

Small lifestyle changes, combined with regular screening, can make an important difference.