Colorectal cancer: overview, signs, causes, diagnosis and management

Common signs and symptoms

Early disease may be asymptomatic. When symptoms occur, they can include:

• Rectal bleeding or blood in the stool
• Persistent change in bowel habits (diarrhoea, constipation, narrowed stools)
• Unexplained iron-deficiency anemia and associated fatigue
• Unintentional weight loss and abdominal discomfort
• A feeling of incomplete bowel emptying, or tenesmus (more common with rectal tumours)

Causes and risk factors

Colorectal cancer develops when normal cells in the intestinal lining acquire genetic changes that allow uncontrolled growth. Most cases are sporadic, but recognised risk factors include increasing age, a family history of colorectal cancer, hereditary syndromes such as Lynch syndrome and familial adenomatous polyposis, long‑standing inflammatory bowel disease (ulcerative colitis or Crohn’s disease), certain dietary patterns, obesity, smoking and heavy alcohol use. Genetic testing and family history can help identify people at high inherited risk.

Diagnosis and staging

Suspicion is usually followed by endoscopic examination. Colonoscopy with biopsy is the diagnostic standard because it allows direct visualisation and tissue sampling. Less invasive screening tests include faecal immunochemical tests and stool DNA tests. Imaging such as CT scans or MRI assesses local extent and distant spread; staging guides treatment planning and commonly follows established systems to describe tumour depth and spread to lymph nodes and distant organs.

Treatment and prognosis

Treatment depends on tumour location, stage and patient health. Surgery is the main curative treatment for localized disease. Rectal cancers often require a combination of surgery with radiotherapy and chemotherapy. Advanced disease may be managed with systemic chemotherapy, targeted biological agents and, increasingly, immunotherapy in selected patients. Prognosis varies widely: early-stage cancers treated surgically have good long-term survival, while survival declines for cancers detected at later stages.

Prevention, screening and notable considerations

Screening substantially reduces deaths by detecting cancer early and removing precancerous polyps. Recommended methods and ages for screening differ by country and individual risk; common approaches include colonoscopy and faecal tests. Lifestyle measures — a diet high in fibre and low in processed red meat, regular physical activity, maintaining a healthy weight, and avoiding tobacco and excessive alcohol — can lower risk. People with a family history or hereditary risk should seek genetic counselling and earlier surveillance. For more clinical details and patient resources see colon and rectal cancer information, anatomy references such as the large intestine overview, and site-specific guidance for the rectum and related conditions.