Familial adenomatous polyposis

Definition

• • Inherited condition in which numerous polyps form mainly in the epithelium of the large intestine

  • While these polyps start out benign, malignant transformation into colon cancer occurs when not treated

Risk Factors

Differential diagnosis

Epidemiology

• • incidence of the mutation is between 1 in 10,000 and 1 in 15,000 births

  • By age 35 years, 95% of individuals with FAP have polyps

Aetiology

• • Development of hundreds to thousands of polyps

Clinical features

• • Blood in stool

  • Anaemia

• weight loss

  • altered bowel habit

  • pigmented lesions of the retina ("CHRPE - congenital hypertrophy of the retinal pigment epithelium")

  • jaw cysts

• sebaceous cysts

• osteomata

Pathophysiology

• • mutations in the APC gene

    • TSG

  • inherited in an autosomal dominant pattern

Investigations

• • Colonoscopy is considered the diagnostic test of choice

    • can provide not only a quantification of polyps throughout the colon but also a histologic diagnosis

  • Barium enema and virtual colonoscopy can suggest the diagnosis of FAP

  • Once the diagnosis of FAP is made, close colonoscopic surveillance with polypectomy is required

  • Ultrasound of the abdomen and blood tests evaluating liver function are often performed to rule out metastasis to the liver.

  • Genetic testing provides the ultimate diagnosis in 95% of cases

Management

a) conservative

b) medical

c) surgical

• • Prophylactic colectomy is indicated if more than a hundred polyps are present, if there are severely dysplastic polyps, or if multiple polyps larger than 1 cm are present

Prognosis

• • Without colectomy, colon cancer is virtually inevitable

  • The mean age of colon cancer in untreated individuals is 39 years (range 34–43 years).