Colon cancer is often described as a disease that develops silently, with many cases beginning as small, non-cancerous growths called polyps that may cause no noticeable symptoms for years.

However, when symptoms do appear, they can be easy to overlook. Changes in bowel habits, tiredness, abdominal discomfort or blood in the stool are often blamed on less serious conditions such as haemorrhoids, irritable bowel syndrome (IBS) or dietary changes.

While these explanations are common, persistent or unexplained symptoms should not be ignored.

'Many colon cancer cases start off slowly as small, benign growths called polyps that are usually symptom-free for many years,' said Dr Edmundo Rodriguez-Frias, MD, medical contributor at Full of Life and a double-board-certified physician in gastroenterology and geriatrics.

'Regular screenings are essential as they help doctors identify and remove potentially dangerous polyps before it becomes too late.'

What Is Colon Cancer?

Colon cancer, also known as colorectal cancer when it affects the colon or rectum, develops when abnormal cells in the lining of the large intestine begin growing uncontrollably.

According to the World Health Organisation, colorectal cancer is one of the most common cancers worldwide, accounting for almost 1.9 million new cases and 900,000 deaths in 2022 alone.

In the UK, colorectal cancer is the fourth most common cancer, with approximately 48,200 new cases diagnosed each year, according to Cancer Research UK.

Although the risk increases with age, cases among younger adults have been rising in recent years. This means symptoms should not automatically be dismissed because someone is considered 'too young' to have the disease.

Changes in Bowel Habits

One of the earliest warning signs of colon cancer can be a noticeable change in bowel movements.

This may include:

  • Persistent constipation or diarrhoea
  • Changes in stool consistency
  • More frequent bowel movements
  • Narrower stools than usual
  • A feeling that the bowel has not completely emptied after going to the toilet

Dr Rodriguez-Frias explained that symptoms can vary depending on where a tumour develops in the colon.

'Right-sided colon cancers typically produce symptoms related to chronic anaemia and fatigue produced by slow and invisible bleeding,' he said.

'Conversely, left-sided tumours tend to create obvious rectal bleeding along with other symptoms like constipation, narrower stools and variations in bowel function.'

Occasional bowel changes are common and may be caused by infections, diet or stress. However, changes that continue for several weeks should be checked by a healthcare professional.

Blood in the Stool or Rectal Bleeding

Stooling
Blood in the stool, whether bright red or darker in colour, should always be checked by a doctor, as it can be a warning sign of colon cancer as well as other digestive conditions. Gpointstudio via Magnific

Finding blood in the stool is one of the symptoms people should never ignore.

Blood may appear bright red on toilet paper or the surface of stools, or it may make stools appear darker.

Although rectal bleeding can be caused by conditions such as haemorrhoids, anal fissures or inflammatory bowel disease, it can also be a sign of colon cancer.

'Most people attribute these symptoms to haemorrhoids, irritable bowel syndrome, or a change in diet,' said Dr Rodriguez-Frias.

'However, while those conditions far exceed the incidence rate of colon cancer, all symptoms of this nature require a doctor's diagnosis instead of self-diagnosing.'

Unexplained Tiredness and Iron Deficiency Anaemia

Persistent fatigue can sometimes be linked to colon cancer, particularly when caused by slow blood loss inside the digestive tract.

This blood loss may not always be visible but can gradually reduce iron levels, leading to iron deficiency anaemia.

Symptoms of anaemia may include:

  • Feeling unusually tired
  • Shortness of breath
  • Dizziness
  • Pale skin
  • Reduced energy levels

'Chronic low-iron anaemia that cannot be explained' is among the early indications of colon cancer, according to Dr Rodriguez-Frias.

People experiencing ongoing fatigue without an obvious cause should speak to their GP, particularly if it occurs alongside digestive symptoms.

Persistent Abdominal Pain or Discomfort

Abdominal pain, cramping, bloating or discomfort that does not improve may also require medical attention.

Colon cancer can sometimes cause narrowing or blockage in the bowel, leading to pain, changes in digestion or a sensation of fullness.

However, abdominal discomfort alone does not necessarily mean someone has cancer. Many digestive conditions can cause similar symptoms, which is why proper assessment is important.

Unexplained Weight Loss

Losing weight without changing diet, exercise habits or lifestyle can be a warning sign of several health conditions, including colon cancer.

Cancer cells can alter the way the body uses energy, while symptoms such as reduced appetite, digestive problems or discomfort may also contribute to weight loss.

Unexpected weight loss, especially when combined with bowel changes, bleeding or fatigue, should be discussed with a healthcare professional.

Why Younger Adults Should Not Ignore Symptoms

Colon cancer has traditionally been associated with older adults, but diagnoses among people under 50 have increased in many countries.

'There has been a significant rise in colorectal cancer diagnosed in individuals under 50 years old,' said Dr Rodriguez-Frias.

'The exact reasons for this trend continue to be studied. Nonetheless, young adults with rectal bleeding or continuing digestive problems should not write off their issues based solely on age.'

Experts say delayed diagnosis can happen when younger people assume their symptoms are caused by stress, diet or common digestive issues.

Seeking medical advice does not mean symptoms are cancer-related, but early investigation can help identify the correct cause.

The Importance of Screening

Screening remains one of the most effective ways to detect colorectal cancer early.

Depending on age, risk factors and location, screening may involve stool-based tests or a colonoscopy.

Colonoscopies allow doctors to examine the inside of the bowel and remove certain polyps before they become cancerous.

'Screening continues to be our best option for detecting colon cancer,' said Dr Rodriguez-Frias.

'Colonoscopies provide the ability to remove pre-cancerous polyps during the same procedure. Early discovery provides more alternatives for treating colon cancer and greatly increases survival rates.'

When Should You Speak to a Doctor?

You should seek medical advice if you experience:

  • Blood in your stool
  • Persistent changes in bowel habits
  • Unexplained weight loss
  • Ongoing abdominal pain
  • Unexplained iron deficiency anaemia
  • Persistent fatigue
  • A feeling that your bowel does not fully empty

Most of these symptoms can have causes other than cancer, but getting checked can provide reassurance and ensure serious conditions are identified as early as possible.

Colon cancer often develops gradually, which means recognising warning signs and attending recommended screenings can make a significant difference. Early diagnosis generally provides more treatment options and improves the chances of successful outcomes.

In Sum

Colon cancer symptoms can be subtle, but changes that persist should never be dismissed as simply part of getting older, stress or a minor digestive issue.

While symptoms such as bowel changes, rectal bleeding, fatigue and unexplained weight loss are often caused by less serious conditions, they still require proper medical assessment.

Paying attention to your body, attending recommended screening appointments and seeking advice when something feels unusual can help detect colon cancer earlier, when treatment is often more effective.

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