The lowdown on Lynch syndrome
Kate Broun investigates the cause and affects of Lynch syndrome, and what GPs can do to ensure appropriate and effective screening of patients.
Lynch syndrome is caused by a mutation in one of four mismatched repair genes (MLH1, MSH2, MSH6, and PMS2) which is linked with clusters of cancer in an individual’s family history. It is most commonly associated with colorectal cancer, as well as endometrial, gastric, ovarian, urothelial and small bowel cancers. Other characteristics include the development of multiple cancers and proximal colon cancers.
In fact, Lynch syndrome is the most common form of hereditary bowel cancer. Between 314 and 512 (or two to four per cent) of all new colorectal cases of cancer are likely due to the mutation. This number is even higher for younger diagnoses with approximately 10-15% of colorectal cancers diagnosed before the age of 50 caused by the high-risk mutations.
Previously known as Hereditary Non-Polyposis Colorectal Cancer (or HNPCC), what we now know as Lynch syndrome was named in honour of physician Dr. Henry T Lynch. Dr. Lynch identified the syndrome after undertaking groundbreaking research into the medical history of two extended families in the 1960s.
To put it simply, everyone has the genes associated with Lynch and normally they are involved in preventing cancers. Lynch syndrome occurs if one of these genes changes and mutates. It’s hereditary and in 50% of cases the faulty gene will be passed from parent to child; it’s like a toss of a coin. Having the gene does not mean that the patient will develop cancer, and it is possible for cancer (but not the gene) to skip a generation.
Practice guidelines recommend that individuals who carry this mutation are offered tailored cancer surveillance, including yearly screening via colonoscopy for colorectal cancer from a younger age. It’s suggested that this regular screening can reduce an individual’s risk of colorectal cancer by 77%  .
As a GP, assessing an individual’s family history of cancer will help you to determine who should be tested for gene mutations, and will inform decisions around cancer surveillance and the optimal timing and frequency of screening. An assessment of family history should cover three generations, including first and second degree relatives.
Look out for these red flags to help you diagnose Lynch syndrome:
• cancer in three or more relatives on the same side of the family
• cancer diagnoses in two successive generations
• one or more of the Lynch related cancers is diagnosed under the age of 50.
Where there is uncertainty on family history, the patient should be encouraged to seek clarification within their family, including details about which relatives have had cancer and their age of diagnosis.
When an individual’s risk is high, referral to a Familial Cancer Centre is recommended for assessment. The centres provide GPs with guidance around what type of screening or testing is available for the family, based on their family history. You can access a list of Familial Cancer Clinics in Australia here.
To learn more about Lynch syndrome, check out the 1-hour education module Appropriate referrals to Familial Cancer Centres for Lynch syndrome risk or click here to access more education and resources from Cancer Council Victoria.
-  American Gastroenterological Association (2015)
Kate Broun is the Manager of Screening, Early Detection and Immunisation at Cancer Council Victoria. She has extensive experience in health promotion, screening and women’s health.