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Updated: Dec 15 2021

Familial Adenomatous Polyposis

  • Snapshot
    • A 40-year-old woman presents to her primary care physician with pallor and fatigue. She complains of easy bruising in the past few weeks. A blood test comes back with values consistent with iron-deficiency anemia. On rectal exam, her PCP can feel discrete polyps. Pale red blood coats his finger after the exam. She is adopted and knows no family history of colon cancer. She is sent for a colonoscopy as soon as possible.
  • Introduction
    • Thousands of polyps in intestinal tract from genetic mutation
    • Genetics
      • autosomal dominant (AD)
      • inactivating mutation in APC gene (adenomatous polyposis coli) on chromosome 5
        • tumor suppressor gene
        • 2-hit hypothesis
      • remember, loss of APC is beginning of path to colorectal cancer
    • Associated conditions
      • Gardner syndrome
        • AD subtype of FAP with bony and soft tissue tumors
      • Turcot syndrome
        • variants include autosomal recessive (AR) or AD with colonic polyposis and medulloblastoma or glioblastoma multiforme
      • ↑ risk for colorectal cancer
        • start screening with sigmoidoscopy at age 12 annually
      • ↑ risk for other cancers
        • hepatoblastoma
        • thyroid cancer
        • pancreatic cancer
  • Epidemiology
    • Average age of presentation with symptoms is 36 years
    • Average age of first polyp is 16 years
  • Presentation
    • Symptoms
      • thousands of polyps develop at a young age
        • rectum always involved
        • pedunculated or sessile
      • rectal bleeding or bloody stool
      • diarrhea
      • abdominal discomfort
    • Physical exam
      • if Gardner syndrome
        • may have epidermal cysts or fibromas
        • may have desmoid tumors in extremities
        • may have osteomas in long bones
      • rectal polyps may be palpable on rectal exam
      • ocular findings
        • congenital hypertrophy of retinal pigment epithelium
        • predicts FAP with 42% sensitivity and 97% specificity
  • Evaluation
    • Based on endoscopy, family history, and genetic testing
    • Complete blood count with iron deficiency anemia
    • Endoscopy with biopsy
      • > 100 colorectal adenomatous polyps
      • tubular adenomas with dysplasia
    • Genetic testing
      • APC mutation
  • Differential
    • Peutz-Jegher syndrome
    • Lynch syndrome
  • Treatment
    • Prophylactic surgical colectomy
    • If severe duodenal polyposis
      • pancreatoduodenectomy
    • Routine screening with colonoscopy and endoscopy
  • Complications
    • Inevitable progression to colorectal cancer if no surgery
    • At risk for other malignancies
      • duodenal cancer
      • hepatoblastoma
      • thyroid cancer
      • pancreatic cancer
  • Prognosis
    • Almost normal prognosis with colonic screening and colectomy
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