Colorectal cancer, cancer of the colon or rectum, is the most common cancer in Singaporean men and the second most common in Singaporean women. Approximately 2,100 new cases are diagnosed in Singapore each year. Despite this prevalence, colorectal cancer remains one of the most preventable and curable cancers in medicine when it is detected early. The majority of colorectal cancers develop slowly over 10-15 years from pre-cancerous polyps -- a timeline that gives screening an extraordinary opportunity to prevent cancer before it starts.
Colorectal cancer is also one of the most mismanaged conditions in terms of symptom recognition. Rectal bleeding -- the most common early symptom -- is routinely attributed to haemorrhoids without further investigation. This assumption costs lives. While haemorrhoids are the most common cause of rectal bleeding, they cannot be distinguished from colorectal cancer bleeding on symptoms alone. Colonoscopy is the only definitive test.
How Colorectal Cancer Develops: The Polyp-to-Cancer Pathway
The vast majority of colorectal cancers do not arise spontaneously -- they develop from adenomatous polyps, small growths that form on the inner lining of the colon or rectum. This polyp-to-cancer progression follows a predictable, slow timeline:
- Adenomatous polyp forms: Genetic changes cause a small polyp to develop in the normal lining of the colon or rectum.
- Polyp grows: The polyp slowly grows over many years and becomes more abnormal, developing from a tubular to a villous adenoma.
- Low-grade dysplasia: Cells become slightly abnormal but have not invaded the bowel wall.
- High-grade dysplasia: Cells become very abnormal but are still limited to the inner lining (mucosa).
- Invasive carcinoma: Cancer cells break through the inner lining and invade deeper layers of the bowel wall.
- Regional spread: Cancer spreads to nearby lymph nodes.
- Distant metastasis: Cancer spreads to other organs, most commonly the liver, but also the lungs or peritoneum.
This entire sequence takes approximately 10-15 years in most patients. This is the biology that makes colonoscopy so powerful: removing a polyp at any point in this sequence permanently interrupts the pathway. A polyp removed is a cancer prevented.
Colorectal Cancer in Singapore: The Local Context
Singapore's colorectal cancer epidemiology has specific characteristics that are clinically important:
- Most common cancer in Singaporean men: Ahead of lung and prostate cancer. Second most common in women, after breast cancer. Singapore Cancer Registry data consistently places CRC at the top of male cancer incidence.
- Rising incidence in under-50s: Rates of colorectal cancer in adults under 50 have been increasing globally and in Singapore. This has led major oncology societies to lower their recommended screening age from 50 to 45. Young-onset CRC often presents at a more advanced stage because symptoms are dismissed in younger patients and screening is not routinely offered.
- High proportion of left-sided tumors: Rectal and sigmoid tumours are more common in Singapore than in Western populations, meaning that symptoms (particularly rectal bleeding and altered bowel habit) are more likely to occur earlier in the disease course.
- Lower screening uptake than optimal: Despite CRC being the most prevalent cancer in men, colonoscopy uptake in Singapore remains below the level needed to meaningfully reduce incidence. The National Cancer Centre Singapore and Singapore Cancer Society recommend colonoscopy from age 50 (or 45 for higher-risk individuals).
Symptoms of Colorectal Cancer
Early-stage colorectal cancer almost never causes symptoms. The absence of symptoms does not mean the absence of disease -- it means screening is even more important. When symptoms do appear, they should prompt prompt medical assessment without delay.
Symptoms that always require assessment
- Blood in the stool or rectal bleeding: The most important symptom. Blood may be bright red (typically from lower rectal or anal lesions), dark red (from the sigmoid or descending colon), or mixed through the stool. Do not assume haemorrhoids without a medical assessment.
- A persistent change in bowel habits: Looser stools, diarrhoea, constipation, or a change in stool calibre (narrower stools) persisting for more than 4 weeks without a clear cause. The change may alternate between diarrhoea and constipation.
- A feeling of incomplete bowel emptying (tenesmus): Particularly associated with rectal cancer, where the tumour creates the sensation that the rectum has not fully emptied
Symptoms of more advanced disease
- Unexplained abdominal pain or cramping: Particularly if persistent and not related to eating or bowel movements
- Unexplained weight loss: Loss of more than 3-5 kg over weeks to months without dietary change or increased exercise
- Fatigue and breathlessness: From anaemia caused by chronic occult blood loss; this may be the only symptom in right-sided (ascending) colon cancer where the tumour bleeds slowly and imperceptibly
- Abdominal mass: A palpable lump in the abdomen, which may represent the tumour itself or involved lymph nodes
- Symptoms of bowel obstruction: Severe cramping, bloating, and inability to pass stool or gas, which may develop if the tumour grows to obstruct the bowel lumen
Risk Factors for Colorectal Cancer
Lifestyle and dietary risk factors
- Diet high in red and processed meat: The strongest dietary risk factor; increases risk by approximately 15-30% per 50g of processed meat consumed daily
- Low dietary fibre intake: Reduced transit time and increased carcinogen contact with the mucosa
- Obesity: Excess body fat, particularly visceral adiposity, is associated with a 30-50% increase in CRC risk
- Physical inactivity: Sedentary lifestyle is independently associated with increased CRC risk
- Tobacco smoking: Increases CRC risk by approximately 20-30%
- Excessive alcohol consumption: Associated with a dose-dependent increase in risk; two or more drinks per day increases risk by approximately 20%
Medical and personal history
- History of adenomatous polyps: Particularly advanced adenomas (large size, villous histology, high-grade dysplasia); the most important individual risk factor for future CRC
- Inflammatory bowel disease: Crohn's disease and ulcerative colitis significantly increase CRC risk, proportional to the extent and duration of disease; annual colonoscopy surveillance is recommended after 8-10 years of disease
- Type 2 diabetes: Associated with a 30-50% increase in CRC risk through insulin resistance and IGF-1 pathway activation
- Prior colorectal cancer: A history of treated CRC increases risk of a metachronous (new) colorectal cancer; regular surveillance is essential
Family history and hereditary syndromes
- First-degree relative with CRC: Doubles lifetime risk; earlier screening (from age 40 or 10 years before the youngest affected relative's age at diagnosis) is recommended
- Lynch syndrome: The most common hereditary CRC syndrome. Lifetime CRC risk of 50-80%. Colonoscopy is recommended every 1-2 years from age 20-25.
How Colorectal Cancer is Diagnosed?
Diagnosis combines clinical assessment, colonoscopy with biopsy for tissue confirmation, and imaging for staging. The complete diagnostic workup is performed before treatment decisions are made.
- Faecal Immunochemical Test (FIT): A simple stool test that checks for small amounts of blood in the stool. It is used for regular screening in average-risk adults. If the result is positive, a colonoscopy is needed to find the cause. FIT does not diagnose cancer; it identifies people who need further testing.
- Colonoscopy: A flexible camera is used to examine the entire colon and rectum for polyps, tumors, and other abnormalities. Polyps can be removed during the procedure, and suspicious areas can be biopsied for testing. AI-assisted colonoscopy can help improve polyp detection. A complete colonoscopy provides a definitive examination of the bowel.
- CT Colonography: A CT scan creates detailed images of the colon and rectum after they are filled with air. It is less invasive than a regular colonoscopy, but cannot remove polyps or take biopsies. It is useful when a colonoscopy is incomplete, unsuitable, or declined. If an abnormality is found, a colonoscopy is usually needed for further examination and biopsy.
- Biopsy and Histopathology: Tissue samples taken during colonoscopy are examined under a microscope to confirm cancer. It also shows how abnormal the cancer cells are, helps determine the stage and severity of the tumour, and checks for genetic changes that can help guide treatment.
- MRI Pelvis (Rectal Cancer): A detailed MRI scan used to stage rectal cancer. It shows how far the tumour has spread and whether it involves nearby tissues. The results help doctors decide whether chemotherapy and radiotherapy are needed before surgery.
- PET-CT Scan: A scan used in selected colorectal cancer cases to look for cancer spread or recurrence. It is useful when CT results are unclear, before surgery for liver metastases, and to check how well treatment is working.
Colorectal Cancer in Under-50s: A Growing Concern
One of the most significant trends in colorectal cancer epidemiology is the rising incidence in adults under 50 -- a trend observed in Singapore and globally. Cases in those aged 20-49 have increased significantly over the past two decades, in contrast to stable or declining rates in older age groups where screening has been more widespread.
- Young-onset CRC (under 50) is more likely to present at an advanced stage -- partly because younger patients and their clinicians are less likely to consider the diagnosis, and partly because screening is not routinely offered
- Symptoms in young adults are frequently attributed to other causes: Rectal bleeding to haemorrhoids, bowel habit change to irritable bowel syndrome, fatigue to stress or lifestyle. Diagnostic delay of 6-12 months or more is common.
- Young-onset CRC has a higher proportion of rectal cancers, signet ring cell histology, and MSI-H tumours compared to older-onset CRC
- Family history and hereditary syndromes (Lynch syndrome, FAP) are more likely to be present in young-onset cases; genetic counselling and testing is recommended for anyone diagnosed with CRC under 50
Colorectal Cancer Screening: Who, What, and When
Screening is performed in people without symptoms, to detect cancer or pre-cancerous polyps before they cause clinical problems. For colorectal cancer, screening is one of the most evidence-based and impactful interventions in preventive medicine.
Who should be screened
- Average risk: All individuals aged 50 and above
- Higher risk (start earlier, screen more frequently): First-degree relative with CRC diagnosed under 60 -- start at 40 or 10 years before the relative's diagnosis age. First-degree relative with CRC diagnosed at 60 or older -- start at 40-45.
- Very high risk (specialised programme): Lynch syndrome mutation carriers -- colonoscopy every 1-2 years from age 20-25. FAP -- colonoscopy from age 10-15; prophylactic colectomy when multiple polyps develop.
- IBD patients: After 8-10 years of disease affecting large portions of the colon: annual or biennial colonoscopy surveillance
What screening tests are available
- Faecal Immunochemical Test (FIT): Annual stool test for blood; non-invasive, home-based. Positive result requires colonoscopy. Detects bleeding from cancers and large polyps; does not detect all polyps. Subsidised under Singapore's Screen for Life programme.
- Colonoscopy: The gold standard; examines the entire colon, removes polyps, and provides 10 years of protection if the result is normal. If polyps are found, the next surveillance interval is shortened based on number, size, and histology of the polyps.
- CT Colonography (virtual colonoscopy): Less invasive alternative to colonoscopy; requires bowel preparation; does not allow biopsy; any abnormality found requires colonoscopy follow-up.
AI-assisted colonoscopy uses computer-aided detection (CADe) technology to identify polyps in real time during the procedure, increasing the adenoma detection rate by up to 40% compared to conventional colonoscopy. This technology is particularly valuable for detecting small, flat polyps that have a higher risk of being missed.
Reducing Your Risk of Colorectal Cancer
The following lifestyle measures have strong evidence for reducing colorectal cancer risk:
- Increase dietary fibre: Whole grains, legumes, vegetables, and fruit. Aim for at least 25-30g of fibre per day.
- Reduce red and processed meat consumption: Limit red meat to 2-3 portions per week; minimise processed meat (sausages, bacon, deli meats).
- Maintain a healthy weight: Particularly reducing visceral (abdominal) fat through diet and exercise.
- Regular physical activity: At least 150 minutes of moderate-intensity aerobic activity per week, plus resistance training. Exercise has a direct protective effect on the colonic mucosa independent of its effect on weight.
- Limit alcohol: No more than one standard drink per day.
- Quit smoking: Tobacco is a CRC risk factor, particularly for rectal cancer.
Learn more about AI-assisted colonoscopy to improve colorectal cancer screening here.
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