Colon Cancer Symptoms: Early Signs & When to Seek Medical Help

Colon cancer is one of the most common types of cancer affecting the digestive system. It begins in the inner layer of the large intestine, often developing from small growths called polyps that don’t cause many symptoms and concern at first. Some of these polyps then develop into colon cancer, which then grows. As the signs of early colon cancer don’t always feel urgent, many people overlook them, leading to delayed diagnosis, by which time the disease has reached a more advanced stage. That’s why knowing about the condition and its early signs is key. To help, this blog covers all you need to know about colon cancer, including its symptoms, available treatments, and when to consult a doctor.

What is Colon Cancer?

Colon cancer develops when abnormal cells in the lining of the large intestine begin to grow out of control. These cells can form tumours that may stay in the colon or, in later stages, spread to other parts of the body. Although many cases begin as polyps, not all polyps turn into cancer. There are different types of colon cancer, based on the kind of cells involved. The most common type is adenocarcinoma, which begins in the cells that make mucus to line the colon. Other, less common types include neuroendocrine tumours, gastrointestinal stromal tumours (GISTs), lymphomas, and sarcomas, though these are rare in the colon. The condition typically progresses over time, which is why regular screening is recommended, even in the absence of symptoms.

What Causes Colon Cancer and Who is at Risk?

Colon cancer usually develops when healthy cells in the lining of the colon change and grow uncontrollably. These changes often start in the DNA of the cells and may happen gradually over several years. Several factors may increase the chances of developing colon cancer:

• Age: Colon cancer is more commonly diagnosed in people over 50. However, there has been a noticeable rise in cases among younger adults in recent years, which researchers are still working to understand.
• Family history: Having a first-degree relative (such as a parent, sibling, or child) who has had colon or rectal cancer increases the risk. The risk is even higher if more than one family member is affected or if the cancer develops at a younger age.
• Genetic conditions: Some people inherit specific gene changes that increase their likelihood of developing colon cancer. The most common inherited syndromes are Lynch syndrome and familial adenomatous polyposis (FAP). These conditions can lead to earlier and more frequent growth of cancer-related polyps.
• Inflammatory bowel disease: Long-standing inflammation in the colon from conditions like ulcerative colitis or Crohn’s disease can damage the lining of the intestine and increase cancer risk over time. The longer the inflammation is present, the higher the risk tends to be.
• Diet and lifestyle: Diets high in red meat or processed meats and low in fibre are associated with a higher risk. Physical inactivity, being overweight or obese, smoking, and frequent alcohol consumption may also contribute to colon cancer risk. These lifestyle factors can influence how cells in the colon grow and repair themselves.
• Type 2 diabetes: People with type 2 diabetes may be at greater risk, possibly due to long-term insulin resistance and chronic inflammation linked to the condition.

Having these risk factors does not mean that colon cancer will develop; it only increases the risk. However, being aware of them can help in making informed decisions about screening, lifestyle changes, and when to consult a doctor. Early detection often leads to better outcomes.

What are the Symptoms of Colon Cancer?

Colon cancer may not cause any noticeable symptoms in its early stages, which is why it often goes undetected until it has progressed. When symptoms do appear, they can vary from person to person and may be mistaken for common digestive issues. Some of the more common signs to look out for include:

• Changes in bowel habits: This may include diarrhoea, constipation, or a change in the consistency of stool that lasts for more than a few days.
• Blood in stool: Bright red or dark-coloured blood may be seen in the stool or on toilet paper.
• Unexplained weight loss: Losing weight without trying may be a sign that something is affecting the body’s normal processes.
• Persistent abdominal discomfort: This can include cramping, bloating, or a feeling of fullness, even after a bowel movement.
• Feeling that the bowel doesn’t empty completely: A constant urge to pass stool, even after going to the toilet, may occur.
• Weakness or fatigue: Ongoing tiredness may result from internal blood loss or the body’s response to the cancer.

These symptoms don’t always mean colon cancer is present, as they can also occur with other conditions like infections or irritable bowel syndrome. However, if any of these signs persist or feel unusual, it’s important to consult a doctor for further evaluation. Early attention to symptoms can make a significant difference in how the condition is managed.

How is Colon Cancer Diagnosed?

Diagnosing colon cancer typically begins with a review of symptoms, medical history, and a physical examination. If colon cancer is suspected, doctors may recommend one or more of the following tests to confirm the diagnosis and determine how far the cancer has progressed.

Colonoscopy

A colonoscopy is the most commonly used and reliable method for detecting colon cancer. It involves inserting a long, flexible tube with a camera (colonoscope) into the rectum to view the inside of the colon. This allows the doctor to look for abnormal growths like polyps, which may turn cancerous over time. If anything suspicious is found, the doctor can remove it or take a biopsy (tissue sample) during the same procedure for further testing.

Stool Tests

These non-invasive tests are often used as part of routine screening:

• Faecal Occult Blood Test (FOBT) and Faecal Immunochemical Test (FIT) detect hidden blood in the stool, which may indicate bleeding from a tumour or polyp.

While these tests do not confirm cancer, they can signal the need for more detailed investigation, such as a colonoscopy.

Imaging Tests

Imaging helps in both diagnosis and staging of colon cancer. It shows if a tumour is present and whether it has spread to nearby tissues or organs:

• CT Scan (Computed Tomography): Offers detailed cross-sectional images of the abdomen and pelvis to detect tumours and assess spread.
• MRI (Magnetic Resonance Imaging): Especially useful for viewing the rectum and surrounding tissues in cases of rectal cancer.
• Chest X-ray or PET scan: May be done to check if cancer has spread to the lungs or other parts of the body.

Biopsy

A biopsy is the only way to confirm the presence of cancer cells. During a colonoscopy or sometimes through a needle guided by imaging, a small tissue sample is taken from a suspicious area. A pathologist examines the sample under a microscope to check for cancer cells and determine the type of cancer.

Blood Tests

Although not used to diagnose colon cancer directly, certain blood tests provide supporting information:

• Complete Blood Count (CBC): Can detect anaemia, which may result from chronic blood loss due to a tumour.
• CEA (Carcinoembryonic Antigen) Test: Measures levels of a protein that may be elevated in people with colon cancer. It is mostly used to monitor treatment progress or detect recurrence.

Staging

Once colon cancer is diagnosed, staging determines how far the cancer has spread (metastasised). This step is important for selecting the most effective treatment plan. These may include additional scans, such as a PET-CT.

What are the Available Treatment Options?

Treatment for colon cancer depends on the stage of the disease, the location of the tumour, and the patient’s overall health. In most cases, a combination of treatments may be used to improve the outcome. The main approaches include:

Surgery

Surgery is the most common treatment for colon cancer, especially in the early stages. The aim is to remove the part of the colon that contains the tumour, along with nearby lymph nodes, which helps lower the chances of the cancer coming back.

• Polypectomy or local excision: In very early cases where the cancer is still in a polyp, it can sometimes be removed during a colonoscopy. This is usually done if the cancer hasn’t spread deeper into the colon wall.
• Colectomy (partial or total): In most cases, doctors perform a partial colectomy, where the section of the colon with the tumour and nearby lymph nodes is removed. The remaining parts of the colon are then joined together. In rare cases, the entire colon may be removed (total colectomy).
• Colostomy or ileostomy: If reconnecting the colon is not possible, a colostomy may be needed. This creates an opening in the abdomen for waste to leave the body into a bag. In some cases, this is only temporary and can be reversed after healing.

Chemotherapy

Chemotherapy uses strong medicines to kill cancer cells or stop them from multiplying. It may be used:

• After surgery (adjuvant chemotherapy): To kill any remaining cancer cells and reduce the risk of the cancer coming back.
• Before surgery (neoadjuvant chemotherapy): To shrink the tumour and make it easier to remove.
• In advanced cancer: If the cancer has spread to other parts of the body, chemotherapy may help control it, ease symptoms, and improve quality of life.
• Common side effects include tiredness, nausea, diarrhoea, loss of appetite, and a higher risk of infections. These side effects are usually temporary and manageable.

Radiation Therapy

Radiation therapy uses high-energy rays to kill cancer cells. It is not used as often for colon cancer as it is for rectal cancer, but may still be recommended in specific situations:

• If the tumour has spread to nearby tissues and surgery alone may not be enough.
• To relieve symptoms like pain or bleeding in advanced cases.

Sometimes, radiation is given along with chemotherapy for a stronger effect.

Targeted Therapy

Targeted therapy focuses on specific proteins or genes that help cancer cells grow. These drugs are more precise and usually cause fewer side effects than regular chemotherapy.

• They are mainly used for advanced colon cancer or when the cancer comes back.
• Before starting targeted therapy, doctors may test the tumour for certain gene changes (mutations), such as KRAS, NRAS, or BRAF, which help decide which drugs are likely to work.

Common side effects may include skin rash, diarrhoea, and high blood pressure.

Immunotherapy

Immunotherapy helps the body’s own immune system find and attack cancer cells. However, this treatment only works for certain types of colon cancer. Before starting, doctors check if the tumour has specific features that make it likely to respond to immunotherapy. If the tumour matches, this option may help control the cancer and improve outcomes.

Side effects are usually milder than those of chemotherapy but can include tiredness, skin changes, or stomach upset.

When to See a Doctor?

Many early signs of colon cancer can seem like everyday digestive problems - bloating, mild cramps, or a change in toilet habits. But if these symptoms last for more than a few days or keep coming back, it’s best not to ignore them. See a doctor if you experience:

• Blood in your stool
• A noticeable change in bowel habits (like diarrhoea or constipation) lasting more than a week
• Ongoing abdominal pain or discomfort
• Unexplained weight loss or fatigue
• A feeling that your bowel doesn’t empty fully

Even if the symptoms seem mild, it’s better to get them checked early. Timely consultation allows for proper testing, and if needed, treatment can begin at an earlier stage, improving outcomes.

If you are over 45 or have a family history of colon cancer, regular screenings are also worth discussing with your doctor.

FAQs

How often should I get a colonoscopy?

For most people, a colonoscopy is advised every 10 years starting at age 45. If polyps are found, doctors may recommend repeating the test every 3 to 5 years. Those with a family history of colon cancer or other risk factors may need earlier or more frequent screening. Your doctor can guide you based on your personal risk.

Can colon cancer return after treatment?

Yes, it can. In some cases, the cancer may come back in the same area or spread to other parts of the body. This is why regular follow-up is important after treatment. Doctors usually suggest check-ups, blood tests, scans, or colonoscopies to catch any signs of recurrence early.

How does colon cancer affect bowel habits?

It may cause ongoing constipation or diarrhoea, a feeling that the bowel is not emptying fully, or a change in the shape of the stool. Some people also notice blood in the stool or a frequent need to go. These symptoms can develop slowly, so any lasting change should be checked by a doctor.

Is colon cancer always hereditary?

No, not always. Although people with a family history of colon cancer may be at higher risk, most cases actually occur in those without any known genetic link. In many situations, lifestyle choices, increasing age, and chronic digestive conditions are more likely to contribute to the disease.

Can colon cancer be prevented?

It cannot always be prevented, but certain steps may lower the risk. Eating more fruits, vegetables, and fibre, limiting processed meats, avoiding smoking, staying active, and going for regular screenings can make a difference. Some polyps can also be detected and removed before they turn cancerous.

How often should someone get screened for colon cancer?

Most people with average risk are advised to begin screening from the age of 45. However, those with a family history, inherited conditions, or certain bowel diseases may need to start earlier. A doctor can recommend the right timing and type of screening test based on individual health and risk factors.

Is colon cancer treatable if caught early?

Yes, when detected early, colon cancer is often very treatable and the chances of recovery are higher. This is why regular screening is important so that any changes in the colon can be spotted and treated in time.

Are colonoscopies painful or risky?

A colonoscopy is done under mild sedation, so patients usually feel drowsy but not in pain. Most people only remember little or nothing about the procedure. It’s a safe test, although very rarely it may lead to side effects like minor bleeding or, in very few cases, a small tear in the colon wall.

Can changes in stool colour or shape always mean colon cancer?

Not necessarily. Stool changes can happen due to dietary shifts, infections, or other digestive problems. However, if symptoms like dark or bloody stools, narrow stools, or sudden changes in bowel habits last for more than a few days, it’s a good idea to get them checked.

How long does it take for colon cancer to develop?

Colon cancer usually develops slowly, often over several years. It often begins as small polyps - non-cancerous growths in the colon lining. If these aren’t removed during screening, some may eventually turn cancerous. This long growth period is why regular screening can be effective in preventing the disease.