Definition
Colorectal carcinoma (CRC) describes malignant lesions in the mucosa of the colon (65%) or rectum (35%).
Key Points
- Genetic factors have an important role in the pathogenesis of CRC.
- Sequence of progression from normal mucosa to adenoma-carcinoma
- Most colorectal cancers are left-sided with symptoms of, pain, bleeding or altered bowel habit.
- Prognosis depends mainly on stage at diagnosis.
- Surgery is the only curative treatment. Chemotherapy and radiotherapy are (neo)adjuvant therapies.
- Screening with guaiac faecal occult blood testing (gFOBT) reduces mortality from CRC.
- 20% of patients with CRC present as emergencies.
Epidemiology
Male : female 1.3:1, peak incidence 50+ years increasing in the West.
Aetiology
Predisposing factors in decreasing importance:
- Personal history of CRC or adenomatous polyps.
- Hereditary syndromes (e.g. familial adenomatous polyposis (FAP), Lynch syndrome (HNPCC), juvenile polyposis syndrome,).
- Family history of CRC: having single first degree relative with CRC increases risk × 2
- Inflammatory bowel disease, especially UC.
- Acromegaly – increased colonic adenomas and CRC.
- Obesity, alcohol, smoking, diabetes mellitus, coronary heart disease, renal transplantation, cholecystectomy all associated with increased risk of CRC.
- NSAIDs protect against CRC, as may physical activity, calcium, statins and diet high in vegetables and low in processed/charred red meat.
Pathology
Macroscopic
- Polypoid, ulcerating, annular, infiltrative.
- 75% of lesions are within rectum, sigmoid or left colon.
- 3% are synchronous (i.e. 2nd lesion found at the same time) and 3% are metachronous (i.e. 2nd lesion found later).
Histological
- Adenocarcinoma (10–15% are mucinous adenocarcinoma).
- Staging by TNM classification (Dukes [A–D] not used anymore).
- Spread: lymphatic, haematogenous, peritoneal.
Clinical Features
- Colicky abdominal pain (44%) – tumours which are causing partial obstruction, e.g. transverse or descending colonic lesions
- Alteration in bowel habit (43%) – either constipation or diarrhoea.
- Bleeding (40%), passage of mucus PR, tenesmus (frequent or continuous desire to defaecate) – rectal tumour.
- Weakness (20%).
- Anaemia (11%) – caecal cancers often present with anaemia.
- Weight loss (6%).
Investigations
- Digital rectal examination and faecal occult blood.
- FBC: anaemia.
- U+E: hypokalaemia, LFTs: liver metastases.
- Endoscopy: sigmoidoscopy (rigid to 30 cm/flexible to 60 cm) and colonoscopy (whole colon) – see the lesion, obtain biopsy.
- Double-contrast barium enema – ‘apple core lesion’, polyp.
- CT colonography (‘virtual colonoscopy’) with air or CO2 pneumocolon.
- Preoperative CEA measured for prognostic significance and measure of surgical clearance.
- Trans rectal ultrasound (TRUS) ± MRI to assess primary tumour invasion in rectal cancer.
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