What Are the Early Signs of Colorectal Cancer and When Should You See a Doctor?

Colorectal cancer often causes few or no noticeable symptoms in its earliest stages, making it difficult to recognise based on warning signs alone. When symptoms do occur, changes in bowel habits, rectal bleeding and unexplained abdominal discomfort may be among the earliest signs, although these can also be caused by other less serious conditions.

You should see a doctor if you notice persistent or unexplained changes in your bowel habits, blood in your stool or other concerning digestive symptoms. Even without symptoms, you may benefit from colorectal cancer screening based on your age, family history and other risk factors.

Understanding why colorectal cancer can be difficult to detect, how screening works and which symptoms require medical attention can help you recognise potential warning signs, make informed decisions about screening and seek appropriate care at an earlier stage.

Key Takeaways

• Colorectal cancer may cause no noticeable symptoms until the disease has progressed.
• Changes in bowel habits, rectal bleeding, abdominal discomfort, fatigue and unexplained weight loss may indicate colorectal cancer.
• Early symptoms can resemble common digestive conditions, making colorectal cancer difficult to recognise without testing.
• FIT can detect hidden blood in stool, while colonoscopy allows doctors to identify and remove suitable polyps.
• Persistent or unexplained bowel symptoms warrant medical assessment, while screening may be recommended even without symptoms.

How Can Colorectal Cancer Lead to These Early Signs and Symptoms?

Colorectal cancer may cause noticeable symptoms when a tumour grows large enough to affect normal bowel function, irritate surrounding tissues or cause bleeding within the digestive tract. The symptoms that develop can differ depending on the tumour's location, size and effects on the bowel. Some changes may be subtle at first, while others become more noticeable as the disease progresses.

Changes in Bowel Habits

As a colorectal tumour grows, it may narrow the passage through which stool moves or interfere with normal bowel function. This can lead to persistent constipation, diarrhoea, changes in stool consistency or a feeling that the bowel has not emptied completely after passing stool.

Rectal Bleeding or Blood in the Stool

Colorectal tumours may bleed when their surfaces become fragile or ulcerated. Bleeding from the rectum or lower colon may appear as bright red blood, while bleeding from further along the colon may produce darker stools. Small amounts of bleeding may also go unnoticed without stool testing.

Persistent Abdominal Discomfort

A growing tumour can interfere with the movement of stool and gas through the bowel, potentially causing abdominal cramps, bloating or discomfort. These symptoms may become more pronounced if the tumour causes significant narrowing or a partial bowel obstruction.

Unexplained Fatigue or Weakness

Slow, repeated bleeding from a colorectal tumour can gradually deplete the body's iron stores, leading to iron-deficiency anaemia. This reduces the blood's ability to carry oxygen efficiently and may cause persistent tiredness, weakness, dizziness or breathlessness, even when no visible bleeding is present.

Unexplained Weight Loss

Colorectal cancer may contribute to unintended weight loss through changes in appetite, inflammation and the body's metabolism. Some patients may also eat less because of abdominal discomfort or other digestive symptoms. Unexplained weight loss is generally more concerning when accompanied by other changes in bowel health.

Why Can Colorectal Cancer Be Difficult to Detect in Its Early Stages?

Colorectal cancer can be difficult to detect early because small tumours and precancerous colon polyps may not initially interfere with normal bowel function, allowing them to remain undetected until they grow larger or begin affecting surrounding tissues.

Even when symptoms appear, they may be mild or resemble those of more common digestive conditions. For example, changes in bowel habits may be mistaken for dietary issues or irritable bowel syndrome, while rectal bleeding may be attributed to haemorrhoids. This overlap can make it difficult to recognise when seemingly minor symptoms require further assessment.

Furthermore, early colorectal cancer cannot reliably be identified through symptoms or a routine physical examination alone. Detecting these abnormalities generally requires dedicated screening or diagnostic tests, which are specifically performed to check for signs of colorectal disease rather than as part of a routine health examination. Doctors may recommend these tests based on a patient's:

• Age: Adults aged 50 and above are generally recommended to undergo routine colorectal cancer screening in Singapore, even without symptoms.
• Family history: Having a close relative diagnosed with colorectal cancer or certain colorectal polyps may warrant earlier or more frequent screening.
• Medical history: Previous colorectal polyps, colorectal cancer or conditions such as longstanding inflammatory bowel disease may require closer surveillance.

How Can Screening Help Detect Colorectal Cancer Before Symptoms Develop?

Colorectal cancer screening can identify early cancers and precancerous polyps before they cause noticeable symptoms. By detecting these abnormalities early, doctors can investigate suspicious findings, remove suitable polyps before they become cancerous and recommend treatment when necessary.

Two commonly used methods of colorectal cancer screening are the faecal immunochemical test (FIT) and colonoscopy.

Faecal Immunochemical Test (FIT)

The faecal immunochemical test (FIT) checks a stool sample for small amounts of blood that may not be visible to the naked eye. This can help identify possible bleeding from colorectal polyps or cancers, even when a person has no noticeable symptoms.

FIT is non-invasive and can be performed at home using a stool collection kit. However, it cannot identify the source of bleeding or directly detect abnormalities in the bowel. A positive result generally requires further assessment with a colonoscopy, while a negative result does not completely rule out colorectal cancer.

Colonoscopy

A colonoscopy allows doctors to examine the inner lining of the colon and rectum using a flexible tube fitted with a camera. Unlike FIT, which detects possible signs of bleeding, colonoscopy allows doctors to directly identify polyps, abnormal tissue and other suspicious changes.

During the procedure, suitable polyps can be removed, while tissue samples can be collected from suspicious areas for biopsy. This makes colonoscopy useful for both detecting colorectal cancer and preventing certain cancers from developing through the removal of precancerous polyps.

If colorectal cancer is confirmed, the doctor may recommend additional tests to establish the extent of the disease and plan appropriate colorectal treatment, including surgery.

Seeking Early Colorectal Cancer Assessment With Dr Ho Kok Sun

By the time colorectal cancer causes noticeable symptoms, the disease has likely already progressed beyond its earliest stages. This is why recognising warning signs and undergoing appropriate screening are both important for early detection. If you experience unexplained changes in bowel habits or other concerning symptoms, medical assessment can help identify their cause. For those without symptoms, screening offers an opportunity to detect precancerous polyps or early cancers before they begin affecting bowel health.

At Ho Kok Sun Colorectal, Dr Ho Kok Sun, Consultant Colorectal & General Surgeon, provides specialist assessment for patients with suspected or diagnosed colorectal conditions. As a colorectal cancer doctor, he can evaluate your symptoms and risk factors, recommend appropriate diagnostic tests and advise on further management based on the findings.

If you have concerns about your bowel health or would like to understand your colorectal cancer screening options, contact our clinic to arrange a consultation.

Frequently Asked Questions About Colorectal Cancer Doctors