Handbook of Genetic Counseling/Familial Adenomatous Polyposis

Familial Adenomatous Polyposis

Contracting edit

  • Introductions
  • Assess main concerns of patient
    • How did the referral to the Hereditary Cancer Program come about?
    • What do they hope to gain from the session?
  • Assess knowledge of diagnosis
    • What do they already know about FAP?
    • What do they already know about hereditary cancer?
  • Overview of today's agenda
    • Restate patient's concerns
    • Medical history, family history, genetics of hereditary cancer, inheritance pattern and recurrence risks, testing options and limitations

Review Medical and Family History edit

  • Medical History
    • Any major health concerns?
    • Surgeries or hospitalizations?
    • Colon cancer screening?
  • Family History
    • Other individuals with any type of cancer?
    • Focus on colorectal cancers, pancreatic cancer, thyroid cancer, brain cancer, as well as desmoid tumor cysts in the mandible
    • Screening practices of other family members?
    • Family thoughts about the cause of cancer?
    • Family experiences with cancer?

General Cancer Information edit

  • All cancer is caused by a mixture of genes and environment
    • All cancer is genetic, but not all cancer is hereditary
    • Most cancers (90-95%) are sporadic
  • Cancer Genetics
    • cells in our bodies are constantly growing and dividing
    • certain genes control/regulate cell growth
    • a change in these genes will result in a cell that grows out of control = cancer
      • the changes occur due to damage to the genetic material
      • DNA, genes, chromosomes
      • DNA contains the instructions for making proteins, which determine what cells do and regulate how we develop
      • the DNA must be copied each time a cell divides
      • sometimes a copying mistake, a typo, can occur
    • Hereditary forms of cancer involve a person inheriting one non-working copy of a gene
      • one step closer to developing cancer than a person with two working copies (therefore it is called an inherited predisposition)
      • features of hereditary cancer include:
        • earlier than expected age of onset
        • multiple generations affected
        • bilateral or multiple primary cancers
        • siblings affected

General Colorectal Cancer Information edit

  • Statistics
    • third most common form of cancer
    • most colorectal cancers are sporadic
    • 6% (1/16) lifetime risk for colon cancer in the general population
    • most individuals diagnosed over the age of 50
      • average age of diagnosis is 67
    • risk factors include aging, diet, previous history of adenoma, colorectal cancer, or inflammatory bowel disease
    • about 5% of colon cancer is due to a hereditary predisposition
      • HNPCC (4%) and FAP (1%) are the two known forms
      • more likely to occur before the age of 50

FAP-specific information edit

  • Clinical Characteristics
    • hundreds to thousands of adenomatous polyps in the colon and rectum at an early age
      • 90% of carriers will have polyps by the age of 20
      • virtually all carriers will have polyposis by the age of 35
      • malignancy will occur in virtually 100% of carriers by the age of 40-50
    • Classic FAP diagnosis requires a minimum of 100 polyps
    • Attenuated FAP generally has polyps developing at a later age and occurring proximally (though they may be found throughout the colon and rectum)
    • Gardner Syndrome (a phenotypic variant of FAP) is characterized by polyposis plus soft tissue tumors of the skin (epidermal cysts), osteomas, desmoid tumors, and supernumerary teeth
    • Colon cancer (average age of onset = 39 in FAP patients) is virtually inevitable if the colon is not removed prophylactically
  • Genetics
    • due to mutations in the adenomatous polyposis coli (APC) gene
      • on chromosome 5q
      • autosomal dominant inheritance
      • a tumor suppressor gene
      • both alleles must be mutated for function to be lost
      • more than 700 mutations have been reported
      • most lead to truncation of the APC gene
      • most families have separate and distinct mutations
      • de novo mutations account for about 30% of FAP cases
      • mutations in the germ cell of a parent
  • Screening and Management
    • annual flexible sigmoidoscopy or colonoscopy beginning at age 10-12
      • if polyps are found, they should be removed and a colectomy considered
    • routine upper GI endoscopy
    • if no polyps found by the age of 25, reduce screening frequency to once every two years until age 35, then every three years until age 50, then every 3-5 years after age 50
    • even if a colectomy is performed, life-long surveillance is required due to the association with extracolonic primary malignancies
    • the effectiveness of chemoprevention is not well established
      • the possibility of NSAID's are currently being evaluated in trials
  • Associated Risks
    • primary adenomas and carcinomas of the duodenum
    • desmoid tumors (in 10% of FAP patients)
    • osteomas
    • thyroid carcinoma
    • brain tumors
    • hepatoblastoma
    • hepatopancreatic tumors
    • gastric fundic gland polyps
    • CHRPE (congenital hypertrophy of the retinal pigment epithelium)
  • Risk Assessment
    • autosomal dominant inheritance (50% chance of inheriting it from an affected parent)
    • 30% are de novo mutations
    • penetrance is virtually 100% by the age of 40

Genetic Testing for FAP edit

  • Two indications:
    • testing an individual who has a clinical diagnosis of FAP
    • testing an individual who is a relative of an established mutation carrier
      • testing an unaffected family member in the absence of an established mutation has a significant risk of a false negative result
      • since each family tends to have a unique mutation
  • Protein Truncation Assay
    • the most common commercial test
    • able to identify most classical FAP mutations
    • once a mutation is identified, PTA is virtually 100% accurate in classifying carriers
  • Denaturing Gradient Gel Electrophoresis (DGGE)
    • an alternative method that may be informative when PTA is not
    • involves direct sequencing of a region in which truncation is identified in an affected family member
  • Gene Sequencing
    • maybe used when no other tests are informative
    • uses linkage analysis or flanking polymorphic genetic markers
    • requires a firm diagnosis of FAP in multiple family members
      • is therefore useless in the 30% of cases which are de novo

Resources edit

  • American Cancer Society
  • CancerCare

References edit

  • www.geneclinics.org
  • www.cancer.org
  • FAP background and screening macros (B.C. Hereditary Cancer Program)
  • Module 6: "Hereditary Colorectal Cancer Syndromes" p 43-55
  • "Hereditary Colorectal Cancer: A Guide for Patients and Their Families" by The Steve Atanas Stavro Familial Gastrointestinal Cancer Registry (Mount Sinai Hospital, Toronto, Canada)

FAP resources edit

  • Colon Cancer Alliance
175 Ninth Avenue
New York, NY 10011
Phone: 212-627-7451; toll-free helpline 1-877-422-2030
Fax: 425-940-6147
Email: kelly@ccalliance.org
  • Colorectal Cancer Network
PO Box 182
Kensington, MD 20895-0182
Phone: 301-879-1500
Fax: 301-942-7145
Email: semicolonclub@yahoo.com
  • Genetics of Colorectal Cancer (PDQ)
A service of the National Cancer Institute
  • Hereditary Colon Cancer Association (HCCA)
3601 N 4th Ave, Suite 201
Sioux Falls, SD 57104
Phone: 800-264-6783; 605-373-2067
Fax: 605-336-6699
Email: hcca@dtnet.com
  • IMPACC (Intestinal Multiple Polyposis and Colorectal Cancer)
PO Box 11
Conyngham, PA 18219
Email: impacc@epix.net
  • American Cancer Society
1599 Clifton Rd NE
Atlanta, GA 30329
Phone: 800-227-2345
  • Collaborative Group of the Americas for Inherited Colorectal Cancer

Notes edit

The information in this outline was last updated in 2002.