Genetic testing in families with hereditary colorectal cancer in British Columbia and Yukon: a retrospective cross-sectional analysis.

BACKGROUND

Genetic testing in families with hereditary cancer enables identification of people most likely to benefit from intensive screening and preventive measures; however, the uptake of testing in relatives (known as cascade carrier testing) for hereditary colorectal cancer syndromes has been shown to be low. Our objective was to report rates of familial testing for hereditary colorectal cancer syndromes in a publicly funded hereditary cancer clinic in Canada.

METHODS

A cross-sectional retrospective database review was used to determine testing uptake between 1997 and 2016 for families served by the provincial Hereditary Cancer Program for British Columbia and Yukon. Analyses were conducted for genes associated with syndromes with an increased risk for colorectal cancer, including Lynch syndrome (, , , and ) and familial adenomatous polyposis (), and for additional moderate- to high-penetrance genes (, , , , and ). Descriptive statistics were used and all analyses were 2-tailed.

RESULTS

The study cohort included 245 index patients, with carrier testing performed in 382 relatives. The mean age at family member testing was 41.2 years, and most (61.0%) of the family members who underwent testing were women. The median time between disclosure of index cases and their family member's results was 8.3 months. Among eligible first-degree relatives, 32.6% (268/821) underwent testing in BC. Of 67 cancer diagnoses in family members, most (62.7%) occurred before genetic testing.

INTERPRETATION

A substantial proportion of people at risk for hereditary colorectal cancer do not undergo genetic testing. This gap highlights the need to explore barriers to testing and to consider interventions to promote uptake; more aggressive efforts by hereditary cancer programs are needed to reach this highest risk population.