Classification of Variants of Reduced Penetrance in High Penetrance Cancer Susceptibility Genes: Framework for Genetics Clinicians and Clinical Scientists by CanVIG-UK (Cancer Variant Interpretation Group-UK).

Purpose: Current practice is to report and manage likely pathogenic/pathogenic variants in a given cancer susceptibility gene (CSG) as though having equivalent penetrance, despite increasing evidence of inter-variant variability in risk associations. Using existing variant interpretation approaches, largely based on full-penetrance models, variants where reduced penetrance is suspected may be classified inconsistently and/or as variants of uncertain significance (VUS). We aimed to develop a national consensus approach for such variants within the Cancer Variant Interpretation Group UK (CanVIG-UK) multidisciplinary network.

Methods: A series of surveys and live polls were conducted during and between CanVIG-UK monthly meetings on various scenarios potentially indicating reduced penetrance. These informed the iterative development of a framework for the classification of variants of reduced penetrance by the CanVIG-UK Steering and Advisory Group (CStAG) working group.

Results: CanVIG-UK recommendations for amendment of the 2015 ACMG/AMP variant interpretation framework were developed for variants where (A) Active evidence suggests a reduced penetrance effect size (e.g. from case-control or segregation data) (B) Reduced penetrance effect is inferred from weaker/potentially-inconsistent observed data.

Conclusions: CanVIG-UK propose a framework for the classification of variants of reduced penetrance in high-penetrance genes. These principles, whilst developed for CSGs, are potentially applicable to other clinical contexts.