A family-based approach to cascade genetic testing in a pediatric cancer genetics clinic

Hereditary cancer predisposition disorders account for up to 10% of all pediatric cancers. Genetic counseling for families of the proband includes risk assessment and recommendations for cascade genetic testing for parents and siblings, but there is no standardized method for cascade testing in place resulting in variability in how clinics approach cascade genetic testing. We explored the uptake and outcomes associated with a family-based approach to cascade testing, for non-syndromic cancer predisposition disorders, at a pediatric cancer genetics clinic serving an ethnically diverse patient population. A retrospective chart review was conducted to evaluate test uptake in the parents and siblings of 106 pediatric probands. The study included 99 mothers, 97 fathers, 116 full siblings, and 53 half siblings who were recommended testing due to genetic risk. Of these relatives, 156 (43%) had documentation of completed cascade testing within twenty-four months after the proband's result disclosure. Completion of cascade testing varied by the type of family member and degree of relatedness. 41% of mothers (41/99) were tested in comparison to 26% of fathers (26/97) and 70.6% of full siblings (82/116) were tested compared to 13.2% of half siblings (7/53). Statistical analysis using chi-squared tests revealed that siblings were more likely to have completed testing than parents (p < 0.001). Furthermore, amongst parents, mothers were more likely to complete testing than fathers (p = 0.03) and amongst siblings, full siblings were more likely to complete testing than half siblings (< 0.001). The proband's age (p = 0.008), parents' preferred language (p = 0.002), and interpreter use during visit (p = 0.004) were the factors associated with differences in test uptake amongst siblings, whereas the proband's race/ethnicity (p = 0.019) was the only factor associated with differences in test uptake amongst parents. The most common barriers noted in charts for lack of test completion included country of residence, lack of insurance, and loss to follow-up. In conclusion, we found that test uptake differed significantly among relatives of a proband with siblings being more likely to test than parents. We also found differences in the demographic and clinical factors associated with test uptake in parents and siblings. Future studies need to validate these differences and further explore the underlying cause of variation in test uptake among relatives.