Canadian consensus for the assessment and testing of Lynch syndrome.

Background: Lynch syndrome (LS) is an autosomal dominant cancer predisposition syndrome caused by a germline pathogenic variant, or epigenetic silencing, of a mismatch repair (MMR) gene, leading to a wide cancer spectrum with gene-specific penetrance. Ascertainment, assessment and testing of LS individuals is complex. A Canadian national guideline is needed to ensure equitable access to patient care across the country.

Methods: The Canadian Lynch Syndrome (CDN-LS) working group was formed in 2021, consisting of 37 multidisciplinary LS experts and patient partners. To formulate consensus statements, a national environmental scan, Canadian clinical survey and literature review were undertaken. The e-Delphi method was used to reach consensus statements among the CDN-LS group.

Results: The CDN-LS group voted on 21 statements, and 18 statements were adopted with over 80% agreement, including 16 statements that had over 90% agreement. These statements provide comprehensive guidelines on universal MMR reflex testing, cascade tumour testing ( promoter methylation, , somatic MMR), germline testing, therapeutics and patient advocacy.

Conclusion: This is the first comprehensive Canadian guideline for LS providing guidance to genetic specialists, laboratories, primary care providers and healthcare providers caring for patients with LS. It is endorsed by the Canadian College of Medical Genetics and the Canadian Association of Genetic Counsellors. The consensus statements are presented as a model for standard of care that improves equitable access to health services for LS across the country. Future work should include a national consensus on LS surveillance, with a goal to harmonise LS care across all provincial and territorial healthcare authorities.