Colorectal Cancer

Cancer originating from the epithelial cells lining the colon or rectum, most commonly an adenocarcinoma; fourth most common cancer in the UK

Aetiology

Risk factors

  • Increasing age
  • Male gender
  • Family history
  • Inflammatory bowel disease
  • Diet rich in fat and meat and low in fibre
  • Smoking, excess alcohol intake
  • Diabetes
  • Atherosclerotic disease

Genetic associations

  • Hereditary nonpolyposis colorectal cancer (HNPCC) - a DNA mismatch repair gene, mutation of the HNPCC gene leads to defects in DNA repair, such as Lynch syndrome
    • Lynch syndrome - late onset, < 100 polys, ascending colon more commonly affected, other cancers associated e.g. uterine, gastric
  • Adenomatous polyposis coli (APC) - a tumour suppressor gene, mutation of the APC gene results in growth of adenomatous tissue, such as Familial Adenomatous Polyposis (FAP)
    • FAP - early onset, > 100 polys, 100% risk of developing cancer anywhere in colon, also associated risk of desmoid tumours and thyroid carcinomas

Pathophysiology

  • Most colorectal cancers develop via a progression of normal mucosa to colonic adenoma (colorectal ‘polyps’) to invasive adenocarcinoma
  • Polyps are often an incidental finding - all visible lesions should be removed by endoscopic mucosal resection as all are premalignant, and patient should undergo lifelong surveillance after resection
  • A minimum of 3 separate genetic defects have to occur to allow the progression from adenoma to carcinoma - oncogene activation, loss/mutation of tumour suppressor genes, loss/suppression of genes involved in DNA repair pathway
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Clinical presentation

  • Can preset from positive result from bowel screening program (home FOB for people 50-74 every 2 years), urgent GP referral, or as an emergency presentation (e.g. perforation)

Common clinical features

  • Change in bowel habit
  • Rectal bleeding
  • Weight loss (usually only if associated metastasis)
  • Abdominal pain
  • Symptoms of iron deficiency anaemia

Right sided cancers

  • Abdominal pain
  • Iron-deficiency anaemia
  • Palpable mass in RIF
  • Often present late

Left sided and rectal cancers (majority)

  • Rectal bleeding
  • Change in bowel habit
  • Tenesmus
  • Palpable mass in LIF or on PR exam

Investigations

  • Colonoscopy - gold standard
  • Staging - biopsy, CT chest/abdo/pelvis, MRI for rectal cancers

Management

Surgical resection

  • Curative
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Palliative options

  • Stenting, palliative radio/chemotherapy, defunctioning, bypass