Colorectal cancer is a malignant tumour of the large bowel, usually developing from adenomatous polyps via the adenoma–carcinoma sequence over many years. It is the third most common cancer in the UK and a leading cause of cancer-related death.
🚨 Rectal bleeding, iron-deficiency anaemia, or a persistent change in bowel habit in adults must be investigated urgently.
Adenoma–carcinoma sequence: stepwise mutations (APC → KRAS → p53) drive transformation of polyps into carcinoma
Microsatellite instability (MSI): failure of DNA repair, as seen in Lynch syndrome
Serrated pathway: sessile serrated adenomas progress via BRAF mutations
💡 Most sporadic cancers follow the adenoma–carcinoma sequence; hereditary syndromes often involve MSI.
Increasing age (>50 years)
Family history, hereditary syndromes (Lynch, FAP)
Inflammatory bowel disease (esp. ulcerative colitis)
Lifestyle: obesity, smoking, alcohol, low-fibre high-fat diet
Protective: high-fibre diet, aspirin/NSAIDs, physical activity
Right-sided tumours
Iron-deficiency anaemia (occult bleeding)
Weight loss, fatigue
Loose or dark stools
Left-sided tumours
Change in bowel habit (constipation/diarrhoea)
Rectal bleeding with mucus
Tenesmus (incomplete evacuation)
Advanced disease
Bowel obstruction (colicky pain, vomiting, distension)
Perforation (peritonitis, acute abdomen)
Liver metastases (hepatomegaly, jaundice)
🚨 Iron-deficiency anaemia in an older patient is CRC until proven otherwise.
Colonoscopy with biopsy: gold standard
Flexible sigmoidoscopy: if left-sided disease suspected
CT colonography: alternative when colonoscopy contraindicated
Staging: CT chest/abdomen/pelvis; MRI pelvis for rectal cancer
CEA tumour marker: useful for monitoring, not diagnosis
Surgery: only curative option for localised disease (type depends on tumour site)
Chemotherapy: used in advanced stage or as adjuvant/neoadjuvant therapy
Radiotherapy: mainly for rectal cancer in combination with chemotherapy
Targeted therapy: reserved for selected metastatic cases
🚨 Obstructing or perforated cancers may need emergency surgery or stenting.
Bowel obstruction or perforation
Bleeding → chronic anaemia
Local invasion into adjacent organs
Liver and lung metastases
Faecal immunochemical test (FIT): every 2 years, ages 60–74 in England/Wales, from 50 in Scotland
Colonoscopy if FIT positive
Earlier and more frequent screening for high-risk groups (e.g. Lynch, FAP)
