Genomics in general practice


Familial colorectal cancer
☰ Table of contents


Practice point


A comprehensive family history must be taken and regularly updated to identify patients who may be at risk of familial colorectal cancer (CRC).1

Refer individuals and families who meet high-risk criteria to a family cancer clinic.

Individuals at average or only slightly higher risk do not require a colonoscopy, and should be encouraged to participate in the National Bowel Cancer Screening Program (ie faecal occult blood test [FOBT]).1,2

 


What do I need to know?


Highly penetrant gene variants in several genes are associated with specific familial CRC syndromes:

  • Lynch syndrome (associated with a range of cancers, including colorectal, endometrial, ovarian, gastric, renal pelvis, ureter, small bowel, biliary tract, brain) is caused by dominantly inherited pathogenic variants in the MLH1, MSH2, MSH6 or PMS2 genes. Lynch syndrome accounts for up to 6% of all colorectal cancer.3
  • Familial adenomatous polyposis (FAP), associated with multiple adenomas in the large bowel, is caused by dominantly inherited pathogenic variants in the APC gene. FAP accounts for approximately 1% of colorectal cancer cases.3
  • There are other rare inherited CRC syndromes that may be associated with specific polyp pathologies, phenotypic features or other cancer types in a family.4,5

Features within a family that are suggestive of increased risk of carrying a pathogenic variant for Lynch syndrome or FAP include:1,5

  • multiple affected relatives on the same side of the family
  • multiple CRCs in the same person (ie metachronous)
  • CRC diagnosed <50 years of age
  • other Lynch–syndrome related cancers (as above)
  • >20 adenomas in the large bowel
  • adenomas diagnosed <30 years of age.

A three-generation family history is key to identifying high-risk families who are most likely to benefit from genetic testing. Such a history should include first-degree and second-degree relatives on both sides of the family. Type of cancer (including whether the cancer is metachronous) and age of onset should be recorded where available.1

Use existing risk criteria to identify families at increased risk of an inherited CRC syndrome (high risk), or individuals who may require additional screening or chemoprevention (moderately increased risk).1


Genetic testing


Family cancer clinics will assess individual risk to determine the utility of genetic testing for Lynch syndrome or FAP. As new genetic variants predisposing to CRC are identified, these new variants may be offered as part of a panel of genetic tests through family cancer clinics.1

There is currently no role in general practice for ordering a cancer-risk assessment based on a single nucleotide polymorphism (SNP) profile (genotyping).


When should I refer?


The recommended CRC screening strategy and different individual risk categories are outlined in The Royal Australian College of General Practitioners’ (RACGP’s) 2016 Guidelines for preventive activities in general practice .1

 

Other considerations


Individuals at increased risk for CRC should be encouraged to:

  • discuss their family history with all first-degree relatives
  • advise family members to discuss their risk with their general practitioners (GP).
 


Resources for general practitioners



Resources for patients


Information

Support


Genomics in general practice




 

 

  1. The Royal Australian College of General Practitioners. Guidelines for preventive activities in general practice. 9th edn. East Melbourne, RACGP, 2016.  [Accessed 19 December 2017].
  2. The Royal Australian College of General Practitioners and Choosing Wisely Australia. Tests, treatments and procedures clinicians and consumers should question. Sydney: NPS MedicineWise, 2016. [Accessed 19 December 2017].
  3. Win AK, Ouakrim, DA, Jenkins, MA. Risk profiling: Familial colorectal cancer. Cancer Forum (Cancer Council Australia) 2014;38(1):15.
  4. Samadder NJ, Jasperson K, Burt RW. Hereditary and common familial colorectal cancer: Evidence for colorectal screening. Dig Dis Sci 2015;60(3):734–47.
  5. Rubenstein JH, Enns R, Heidelbaugh J, Barkun A. American Gastroenterological Association Institute guideline on the diagnosis and management of Lynch syndrome. Gastroenterology 2015;149(3):777–82.

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