Abstract Background Whether carriers of BRCA1 or BRCA2 (BRCA1/2) pathogenic variants (PVs) have increased risks of childhood, adolescent, and young adult (CAYA) cancers is controversial. We aimed to evaluate this risk and to inform clinical care of young BRCA1/2 PV carriers and genetic testing for CAYA cancer patients. Methods Using data from 47,117 individuals from 3,086 BRCA1/2 families, we conducted pedigree analysis to estimate relative risks (RRs) for cancers diagnosed before age 30. Results Our data included 274 cancers diagnosed before age 30: 139 breast cancers, 10 ovarian cancers, and 125 non-breast non-ovarian cancers. Associations for breast cancer in young adulthood (20-29 years) were found with RRs of 11.4 (95% CI: 5.5, 23.7) and 5.2 (95% CI: 1.6, 17.7) for BRCA1 and BRCA2 PV carriers, respectively. No association was found for any other investigated CAYA cancer, nor for all non-breast non-ovarian cancers combined: the RRs were 0.4 (95% CI: 0.1, 1.4) and 1.4 (95% CI: 0.7, 3.0) in BRCA1 or BRCA2 PV carriers, respectively. Conclusion We found no evidence that BRCA1/2 PV carriers have an increased CAYA cancer risk aside from breast cancer in women in their 20’s. Our results, along with a critical evaluation of previous germline sequencing studies, suggest that the childhood and adolescent cancer risk conferred by BRCA1/2 PV would be low (ie, RR &amp;lt; 2) if it existed. Our findings do not support PV testing for offspring of BRCA1/2 PV carriers at ages &amp;lt;18 years, nor for conducting BRCA1/2 PV testing for childhood and adolescent cancer patients.

Childhood, adolescent and young adulthood cancer risk in BRCA1 or BRCA2 pathogenic variant carriers