Understanding Colorectal Cancer

Colorectal cancer are cancers that develop in the colon or rectum, which form the final section of the digestive tract. The colon absorbs water and nutrients from food, while the rectum stores waste before it is passed from the body.

As both colon and rectal cancer share similar biological features and treatment approaches, they are collectively referred to as colorectal cancer.

Most colorectal cancers begin as polyps—non-cancerous growths on the inner lining of the colon or rectum. While many polyps remain harmless, some can undergo changes over time that cause them to become cancerous. Polyps often do not cause symptoms, which is why routine screening is important to prevent colorectal cancer. In some cases, colorectal cancer develops directly from the innermost lining of the bowel without forming a polyp first. As cancer cells grow, they may extend deeper into the bowel wall, spread into the surrounding fatty tissue or reach nearby lymph nodes.

In more advanced stages of the disease, cancer cells can travel through the bloodstream to organs in other parts of the body, most commonly the liver.

Early detection and timely treatment can significantly improve colorectal cancer outcomes.

Colorectal Cancer Prevalence

Statistics from the latest Singapore Cancer Registry Annual Report 2023 show that colorectal cancer was the second most common cancer in males and females, with close to 13,000 new cases diagnosed in Singapore between 2019 and 2023.

Although colorectal cancer is most often diagnosed in people aged 50 and above, the number of younger adults under 50 being diagnosed with the disease has been increasing. In younger patients, the disease may be linked to hereditary conditions such as familial adenomatous polyposis (FAP) or hereditary non-polyposis colorectal cancer. However, there are many cases that occur in younger individuals without a genetic cause.

Routine screening through regular faecal immunochemical tests (FIT) or colonoscopies plays a crucial role in preventing colorectal cancer. Detecting and removing polyps early can stop them from becoming cancerous and allows earlier detection and treatment when needed.

Symptoms of Colorectal Cancer

Colorectal cancer often develops silently in its early stages, with no noticeable symptoms. As the disease progresses, symptoms may include:

• Persistent diarrhoea or constipation 
• Blood in the stool or visible rectal bleeding 
• Changes in stool shape, size or consistency 
• Abdominal discomfort such as bloating, cramps, gas or a persistent feeling of fullness 
• The feeling that the bowel does not empty completely after going to the toilet 
• Persistent fatigue
• Unexplained loss of appetite or weight loss

When to Seek Medical Advice

While these symptoms may arise from conditions unrelated to colorectal cancer, it is important to consult a doctor promptly if you notice persistent or unusual symptoms . Seeing a doctor promptly about these symptoms allows for early diagnosis and timely access to treatment for colorectal cancer.

How to Reduce the Risk of Colorectal Cancer

While colorectal cancer cannot be completely prevented, there are steps that individuals can take to lower the risk of developing the disease. Most important are leading a healthy lifestyle and going for regular screening.

Importance of Screening

Screening helps to detect polyps or early colorectal cancer before symptoms appear. In Singapore, individuals with no symptoms are advised to begin screening at age 50. Those with a family history of colorectal cancer may be advised by their doctor to start screening at a younger age.

Colorectal cancer screening tests include:

• Annual Faecal Immunochemical Test (FIT): This simple stool test checks for hidden blood in the stool, which may be an early sign of colorectal cancer. If blood is detected, further tests such as a colonoscopy may be recommended. 
• Colonoscopy – every 5 to 10 years: During this procedure, a flexible camera is used to closely examine the colon and rectum. Small polyps can be removed and tissue samples may be taken from any abnormal areas. This helps prevent polyps from developing into cancer.

Lifestyle Habits That Help Protect Against Colorectal Cancer

Adopting these healthy habits can reduce your risk of developing colorectal cancer:

• Choose a diet rich in fruits, vegetables and whole grains, and limit high-fat foods. 
• Avoid smoking or seek help to quit the habit. 
• Limit alcohol consumption. 
• Stay physically active with regular exercise.

These measures, combined with routine screening, offer the strongest protection against colorectal cancer.

Causes and Risk Factors for Colorectal Cancer

Colorectal cancer develops when cells in the colon or rectum go through genetic changes that cause them to grow in an uncontrolled way. These cells may eventually form tumours. The exact reason these mutations occur is not fully understood, but several factors, such as age, inherited conditions, lifestyle habits and underlying medical issues, can increase the likelihood of developing colon cancer or colorectal cancer.

Having one or more risk factors does not mean you will develop colorectal cancer, but they may raise your overall risk.

Non-modifiable risk factors for colorectal cancer include:

• Older age: Colorectal cancer is most commonly diagnosed in people aged 50 and above, though colorectal cancer can occur in younger adults. 
• Personal history of colorectal polyps or previous colorectal cancer: Past abnormalities can increase future risk. 
• Inflammatory bowel disease: Long-standing ulcerative colitis or Crohn’s disease raises the risk of developing colorectal cancer. 
• Family history or inherited genetic syndromes: Conditions such as familial adenomatous polyposis (FAP) and Lynch syndrome (hereditary non-polyposis colorectal cancer) significantly increase the lifetime risk of developing the disease.

Lifestyle and health-related factors include:

• Diabetes or insulin resistance, which has been linked to a higher risk of colorectal cancer 
• Low-fibre, high-fat diets 
• Physical inactivity or a sedentary lifestyle 
• Smoking 
• Heavy alcohol consumption

Understanding these risk factors helps to guide decisions on screening, prevention and early detection.

Diagnosis of Colorectal Cancer

Diagnosing colorectal cancer involves a combination of tests designed to detect polyps, cancerous growths and other abnormalities in the colon and rectum. Your doctor may recommend bowel preparation, such as a laxative or an enema, before certain procedures to ensure that the colon is fully cleared. Proper preparation is important for accurate results.

Common Diagnostic Tests

• Colonoscopy: A colonoscopy is one of the most reliable tools for detecting colorectal cancer. During this procedure, a flexible camera is inserted through the anus so that the doctor can examine the entire colon and rectum, remove small polyps and take tissue samples (biopsies) from areas that look abnormal. 
• Digital rectal examination (DRE): During a routine physical examination, the doctor may insert a lubricated, gloved finger into the rectum to feel for any irregular lumps or growths. This test may feel slightly uncomfortable but should not be painful. 
• Double-contrast barium enema: During this imaging test, the colon is filled with a liquid called barium, which coats the lining of the intestine. X-rays taken afterward show clearer details, helping to identify any polyps or other abnormalities. 
• Computed Tomographic Colonography (CTC): Also known as a virtual colonoscopy, CTC uses CT scans to create detailed 3D images of the colon. After the colon is gently inflated with carbon dioxide, images are captured which allow doctors to spot any suspicious growths. 
• Flexible sigmoidoscopy: This test uses a thin, lighted tube (a sigmoidoscope) to inspect the rectum and lower part of the colon. It also enables the removal of tissue samples (biopsy) where needed. While it examines only part of the bowel, it can be useful for identifying issues on the left side of the colon.

Tests to Assess the Stage of Cancer

If tests confirm colorectal cancer, your doctor may order additional scans, such as CT or MRI of the abdomen, pelvis or chest, to determine how far the cancer has spread. Staging information helps to guide clinical decisions on the most appropriate cancer treatment. In some cases, the exact stage becomes clear only after surgery, when the removed tissue can be examined more closely.

Treatment for Colorectal Cancer

Colorectal cancer treatment is tailored to the individual and takes into account the size and location of the tumour, how far it has progressed and the overall health of the patient. Care is guided by a multi-disciplinary team that may include colorectal surgeons, medical oncologists, radiation oncologists, interventional radiologists, nuclear medicine physicians and palliative care specialists. Working together, this team recommends the most appropriate treatment approach for each patient.

Types of Treatment

Surgery

Surgery is the main form of treatment for colorectal cancer and is often the first option for disease that has not spread widely. The type of surgery performed depends on how advanced the cancer is.

• Early-stage cancer: When detected early, only the cancerous area or a small section of the inner lining may need to be removed. 
• More advanced cancer: A larger portion of the colon or rectum may be removed, along with the nearby lymph nodes to ensure all cancer cells are removed . In many cases, minimally invasive (laparoscopic) surgery may be possible. This technique uses several small incisions, which can reduce post-operative pain and support a faster recovery, though it is not suitable for every individual.

Some patients may require a stoma, an artificial opening that allows the elimination of stools from the body while the bowel takes time to heal or when the natural pathway is removed. A stoma may be temporary or permanent. Specially trained nurses provide support and education to help patients confidently manage their stoma care.

For some individuals with stage 4 colorectal cancer that has spread to organs such as the liver or lungs, surgery may still play a role in disease control.. Colorectal surgeons and oncology teams collaborate closely with liver, lung and peritoneal specialists to determine the best surgical plan for the patient.

In many cases, chemotherapy or radiation therapy may be used before or after surgery to improve the treatment outcome.

Chemotherapy and Targeted Therapy

Chemotherapy uses anti-cancer medicines to destroy cancer cells in the body. It may be given on its own, combined with targeted therapy or used before or after surgery. Tumour profiling is often performed to understand the individual cancer’s characteristics and to help identify which drugs would be effective.

• Stage 2 and Stage 3 cancer: Chemotherapy (commonly oxaliplatin and fluoropyrimidines) may be prescribed for 3 to 6 months after surgery to reduce the risk of recurrence. Follow-up often continues for five years and may include physical examinations, blood tests, imaging scans and colonoscopy.
• Stage 4 cancer: When cancer has spread to other organs, chemotherapy and/or targeted therapy may be used to shrink tumours and slow disease progression. Treatment options may include: 
  • Oxaliplatin, irinotecan and fluoropyrimidines 
  • Anti-EGFR monoclonal antibodies (panitumumab, cetuximab) 
  • Anti-VEGF monoclonal antibodies (bevacizumab, ramucirumab) 
  • Oral therapies such as encorafenib, regorafenib and TAS-102

Some individuals with limited metastatic spread may also be candidates for further surgery or localised treatments.

Side effects of chemotherapy varies by individual and drug type but may include nausea, diarrhoea, mouth sores, rashes, numbness, low blood counts and, rarely, organ-related complications. These effects are monitored closely, and supportive care is provided throughout treatment.

Radiation Therapy

Radiation therapy uses high-energy X-rays to target cancer cells while aiming to spare as much healthy tissue as possible. It is most commonly used in rectal cancer and may be recommended:

• Before surgery, to shrink a rectal tumour 
• After surgery, to destroy any remaining cancer cells 
• When surgery is not possible, to control symptoms such as pain or bleeding

Immunotherapy

Immunotherapy trains the body’s own immune system to attack and destroy cancer cells. It is usually offered to colorectal cancer patients where the colorectal cancer cells have tested positive for specific gene changes. Treatment is given intravenously and is reserved for selected cases where testing shows it is likely to work.

Supportive (Palliative) Care

Palliative care focuses on improving comfort, relieving symptoms and enhancing quality of life. It can be provided at any stage of colorectal cancer treatment, not only at advanced stages. The palliative care team works alongside the primary treating doctors, to offer support with symptom control, wellbeing and overall care planning.

Pre-Surgery Preparation for Colorectal Cancer

Preparing for colorectal cancer surgery is an important part of your treatment journey. Before surgery , your care team will ensure that you are medically ready and informed about what to expect.

Medical Assessment

Your surgeon will arrange a detailed evaluation, which may include blood tests, imaging scans and a review of your medical history. These assessments help to determine whether you are suitable for surgery and identify any risks that may need to be managed.

The patient’s treatment plan is reviewed by a multi-disciplinary tumour board, where specialists discuss the benefits and considerations of each approach to ensure the most appropriate cancer treatment is delivered.

Anaesthesia Review

Before surgery, the anaesthesia will assess your fitness for general anaesthesia, explain how your pain will be managed after the operation and answer any questions about the procedure.

Pre-Surgery Support

Specialist nurses provide counselling and guidance to help you prepare for surgery. They may give you instructions on medication, diet, stoma-related information (if relevant), and what to expect on the day of surgery.

Post-Surgery Care for Colorectal Cancer

Your doctors and specialist nurses may provide advice on diet, wound care, activity levels and medication post-surgery. If you experience symptoms such as pain, unusual bleeding, fever or changes in bowel habits, you should inform your care team promptly so that appropriate treatment can be started without delay.

Regular Follow-Up Appointments

Follow-up care plays an important role in monitoring your health and ensuring that any concerns are addressed early. After you leave the hospital, you will return for scheduled outpatient reviews with your care team. These appointments allow your doctors to monitor your recovery, assess how well you are healing and detect any signs of the cancer returning. Follow-up care may include :

• Blood tests, including tumour marker checks 
• Imaging scans, such as CT scans or ultrasounds 
• Physical examinations to assess your surgical site and overall wellbeing

Ongoing Monitoring

Consistent follow-up is a key part of long-term colorectal cancer treatment. Even if you feel well, attending all recommended appointments helps your team to identify issues earlywhen they are easier to manage.

Commonly Asked Questions

1. Does colorectal cancer always cause pain?

No, many people with early-stage colorectal cancer do not experience any pain or symptoms . Some tumours grow slowly and do not press on surrounding tissues until they are more advanced. This is why screening for colorectal cancer is important even when you feel well.

2. Can colorectal cancer affect bowel control?

Yes, depending on where the tumour is located, some individuals may notice changes such as urgency, difficulty controlling bowel movements or an increased need to visit the toilet. These symptoms are not always caused by colorectal cancer but should be assessed by a doctor if they persist.

3. Is diet still important after colorectal cancer treatment?

A balanced diet remains important during recovery and for long-term health. Some people may need to adjust their fibre intake, eat smaller meals or avoid foods that trigger discomfort while the bowel heals. A dietitian can give personalised guidance based on your treatment and recovery needs.