What Are the Warning Signs of Colorectal Cancer?

Dr Chong Chee Keong Breast, Colorectal and General Surgeon MBBS (Singapore), FRCS (Edinburgh), FRCS (Glasgow), FAMS (Singapore) Specialist Accreditation in Intensive Care Medicine Specialists Accreditation Board, Medical Director & Senior Consultant

Having these symptoms does not necessarily mean you have colorectal cancer. However, persistent or unexplained changes warrant medical assessment to determine the underlying cause and whether further investigation is needed.

This article explains the warning signs to look out for, when to see a doctor, how colorectal cancer is diagnosed and what may happen if cancer is found.

Key Takeaways

• Colorectal cancer may cause no symptoms in its early stages. When symptoms occur, persistent changes in bowel habits, blood in the stool and unexplained abdominal symptoms are among the signs that warrant assessment.
• Rectal bleeding and bowel changes have many possible causes, so symptoms alone cannot confirm or rule out colorectal cancer.
• Colonoscopy allows the colon and rectum to be examined directly and suspicious tissue to be biopsied for diagnosis.
• Screening is important because colorectal cancer and precancerous polyps can be present before symptoms appear.

What Are the Early Warning Signs of Colorectal Cancer?

Colorectal cancer may cause few or no symptoms in its early stages. When symptoms do develop, they can overlap with common digestive conditions. The following changes warrant medical attention when they persist, worsen or cannot be readily explained.

Changes in Bowel Habits That Persist

A lasting change in bowel habits is one of the most common early signs of colorectal cancer. This may include:

• Diarrhoea or constipation lasting several weeks
• Alternating episodes of diarrhoea and constipation
• A persistent change in the usual size, shape or appearance of stools
• A persistent feeling that the bowel has not emptied completely

A tumour can sometimes affect how stool moves through the colon or rectum, contributing to changes in bowel habits. Similar changes can occur with conditions such as irritable bowel syndrome (IBS) or after changes in diet, so the symptom alone cannot determine the cause.

Blood in the Stool or Rectal Bleeding

Colorectal bleeding may appear as bright red blood on the toilet paper or in the toilet bowl, or as blood mixed with the stool. In some cases, small amounts of bleeding may not be visible and are detected through stool tests or through signs of iron-deficiency anaemia.

Rectal bleeding is not always caused by colorectal cancer. Haemorrhoids, anal fissures and inflammatory bowel disease are other possible causes. However, persistent, recurrent or unexplained rectal bleeding should be medically assessed rather than automatically attributed to haemorrhoids or another benign condition.

Ongoing Abdominal Pain or Bloating

Persistent abdominal symptoms may occur as colorectal cancer develops. These can include:

• Cramping or aching abdominal pain
• Persistent bloating or abdominal fullness
• Discomfort that becomes more frequent or changes from its usual pattern

Abdominal pain and bloating have many possible causes and are not specific to colorectal cancer. They may be more concerning when they are persistent or occur alongside an unexplained change in bowel habits or rectal bleeding.

Unexplained Weight Loss and Fatigue

Colorectal cancer can sometimes cause symptoms that are not obviously related to the bowel. Unexplained weight loss may occur, while slow, ongoing bleeding from a colorectal tumour can lead to iron-deficiency anaemia. Anaemia may cause persistent fatigue, weakness or shortness of breath.

These symptoms have many possible causes, but unexplained weight loss or iron-deficiency anaemia may warrant further investigation, particularly when accompanied by bowel changes or rectal bleeding.

How Is Colorectal Cancer Diagnosed?

If colorectal cancer is suspected, assessment usually begins with a review of your symptoms, medical history and a physical examination. A colonoscopy may then be used to examine the colon and rectum and obtain a biopsy from suspicious tissue. If cancer is confirmed, imaging tests can help determine its extent and guide treatment planning.

Medical History and Physical Examination

The consultation begins with a discussion of your symptoms, medical history and colorectal cancer risk factors. Your doctor may ask about:

• How long your symptoms have been present and whether they have changed
• Your usual bowel habits and any recent changes or rectal bleeding
• A personal or family history of colorectal cancer or colorectal polyps
• A history of inflammatory bowel disease or previous bowel surgery

A physical examination may include examining the abdomen for tenderness, swelling or a palpable mass. A digital rectal examination may also be performed where appropriate to assess the lower rectum.

Colonoscopy and Tissue Biopsy

Colonoscopy is one of the main investigations used when colorectal cancer is suspected. During the procedure, a flexible tube with a camera is passed through the rectum to examine the lining of the colon and rectum for polyps, suspicious growths or other abnormalities.

If a suspicious area is identified, a tissue sample (biopsy) can usually be taken during the same procedure. The sample is then examined under a microscope to determine whether cancer cells are present. Polyps may also be removed during colonoscopy where appropriate.

Imaging Tests for Cancer Staging

If colorectal cancer is confirmed, imaging tests are used to assess the extent of the disease and whether it has spread to nearby structures, lymph nodes or other organs. Depending on the location of the cancer and individual findings, these may include:

• CT scans of the chest, abdomen and pelvis
• MRI, particularly for assessing rectal cancer
• PET scans in selected cases

What Happens If Colorectal Cancer Is Found?

Treatment for colorectal cancer depends on factors such as where the tumour is located, how far the cancer has spread and the patient's overall health. Some patients may be treated with surgery, while others require additional treatment before or after an operation.

What Treatments Are Used for Colorectal Cancer?

The recommended treatment depends on whether the cancer arises in the colon or rectum, its stage and other characteristics identified during assessment. Treatment may include:

• Surgery to remove the affected part of the colon or rectum where appropriate
• Chemotherapy, which may be given before or after surgery depending on the cancer
• Radiotherapy, particularly as part of treatment for some rectal cancers
• Targeted therapy or immunotherapy for selected patients with advanced disease, depending on tumour characteristics

Why Does Early Diagnosis Matter?

Colorectal cancer detected at an earlier stage is generally more likely to be confined to the colon or rectum and may offer more treatment options. In some patients, localised disease can be treated with surgery with curative intent, while cancer that has spread to other organs may require a different combination of treatments.

Working with a Colorectal Cancer Specialist

Colorectal cancer care often involves specialists from different disciplines, including colorectal surgery, medical oncology and radiation oncology where appropriate. A colorectal specialist can explain the surgical aspects of treatment and work with the wider cancer team to develop a treatment plan based on the diagnosis and stage.

Colorectal Assessment and Care in Singapore with Dr Chong

Persistent or unexplained colorectal symptoms warrant medical assessment because their cause cannot be determined from symptoms alone. Depending on the findings, further investigation may be recommended to identify the underlying condition and determine whether treatment is needed.

Maven Surgery provides specialist assessment and surgical care for colorectal conditions in Singapore, including colorectal cancer. Dr Chong Chee Keong is a breast, colorectal and general surgeon with more than 20 years of clinical experience. His practice includes colorectal cancer surgery and minimally invasive surgical approaches where appropriate, working alongside other cancer specialists as part of multidisciplinary care.

If you have persistent colorectal symptoms or concerns about your colorectal cancer risk, you may schedule a consultation to discuss whether further assessment is appropriate.

Frequently Asked Questions (FAQs) About Colorectal Cancer Symptoms