Colon cancer

Overview

Colorectal (colon and rectal) cancer is cancer of the large intestine. Most begin as small, non-cancerous polyps that grow on the inner lining of the colon and may become cancerous over years. Detecting and removing polyps during screening can prevent cancer developing altogether.

How common is it?

Colorectal cancer is the fourth most common cancer in the UK with about 42,000 new cases per year. It is the second most common cause of cancer death.

Causes and risk factors

Most colorectal cancers develop from polyps. DNA changes in colon cells accumulate over years due to a combination of age, diet, lifestyle, and genetic factors.

Common risk factors

• Age over 50
• Diet high in red or processed meat
• Low fibre intake
• Obesity and low physical activity
• Smoking and excess alcohol
• Family history of colorectal cancer or polyps
• Inflammatory bowel disease (Crohn's or ulcerative colitis)
• Inherited syndromes: Lynch syndrome, FAP

Symptoms

• Blood in stools or rectal bleeding
• Change in bowel habits lasting more than 3 weeks (looser stools, increased frequency)
• Unexplained weight loss
• Abdominal pain, cramping, or discomfort
• Feeling that the bowel has not fully emptied
• Unexplained anaemia causing fatigue
• Many early cancers cause no symptoms at all

When to see a doctor

Contact a GP about blood in stools, a persistent change in bowel habit, unexplained weight loss, or other concerning bowel symptoms. Get urgent advice for black or dark-red stools or bloody diarrhoea. Heavy or continuous rectal bleeding requires emergency help. These symptoms do not always mean cancer, and the appropriate tests and referral depend on the clinical assessment.

Diagnosis

Colonoscopy is the gold standard and allows biopsy and polyp removal simultaneously. CT colonography (virtual colonoscopy) is an alternative. Stool testing for faecal occult blood is used in NHS screening. CT scan stages the disease.

Treatments

Self-care and lifestyle

• Participate in NHS bowel cancer screening (faecal immunochemical test at age 50-74)
• Increase dietary fibre from wholegrains, vegetables, and pulses
• Limit red and processed meat intake
• Exercise regularly and maintain a healthy weight

Prevention

Bowel cancer screening finds polyps before they become cancer and is the most effective preventive measure. A healthy diet, active lifestyle, not smoking, and limiting alcohol all reduce risk.