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 these polyps can prevent some bowel cancers.

How common is it?

Colorectal cancer is the fourth most common cancer in the UK. Around 48,200 new cases were diagnosed each year on average in 2019 and 2021-2022. It is a major 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
• A persistent change in bowel habits, such as looser stools or going more often
• 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 allows examination of the bowel, biopsy and polyp removal. CT colonography is an alternative in some cases. NHS screening uses the faecal immunochemical test (FIT), which looks for blood in poo, not cancer itself. FIT is also used to help assess symptoms; a negative result does not exclude cancer. CT scans help assess spread after diagnosis.

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 screening can detect cancer early. A positive FIT may lead to colonoscopy, where polyps can be removed to reduce future cancer risk. Eating more fibre, limiting red and processed meat and alcohol, being active, maintaining a healthy weight and not smoking also reduce risk.