No Association of Early-Onset Breast or Ovarian Cancer with Early-Onset Cancer in Relatives in or Mutation Families.

According to clinical guidelines, the occurrence of very early-onset breast cancer (VEO-BC) (diagnosed ≤ age 30 years) or VEO ovarian cancer (VEO-OC) (diagnosed ≤ age 40 years) in families with or mutation () prompts advancing the age of risk-reducing strategies in relatives. This study aimed to assess the relation between the occurrence of VEO-BC or VEO-OC in families with and age at BC or OC diagnosis in relatives. We conducted a retrospective multicenter study of 448 consecutive families with from 2003 to 2018. Mean age and 5-year-span distribution of age at BC or OC in relatives were compared in families with or without VEO-BC or VEO-OC. Conditional probability calculation and Cochran-Mantel-Haenszel chi-square tests were used to investigate early-onset cancer occurrence in relatives of VEO-BC and VEO-OC cases. Overall, 15% (19/245) of families with and 9% (19/203) with featured at least one case of VEO-BC; 8% (37/245) and 2% (2/203) featured at least one case of VEO-OC, respectively. The cumulative prevalence of VEO-BC was 5.1% (95% CI 3.6-6.6) and 2.5% (95% CI 1.4-3.6) for families with and , respectively. The distribution of age and mean age at BC diagnosis in relatives did not differ by occurrence of VEO-BC for families with or . Conditional probability calculations did not show an increase of early-onset BC in VEO-BC families with or . Conversely, the probability of VEO-BC was not increased in families with early-onset BC. VEO-BC or VEO-OC occurrence may not be related to young age at BC or OC onset in relatives in families with . This finding-together with a relatively high VEO-BC risk for women with -advocates for MRI breast screening from age 25 regardless of family history.