Résumé
Very-early-onset (VEO) breast (under 30) and ovarian (under 40) cancers estimates in women carrying a germline mutation in BRCA1 or BRCA2 (BRCA1/2 women) are inaccurate and inconsistent. This study aimed to measure VEO breast and ovarian cancers cumulative prevalence in BRCA1/2 women. We secondarily aimed to assess the relationship between VEO cancer in BRCA1/2 women and ages at breast and ovarian cancer diagnosis in their relatives, and to seek for phenotype-genotype correlations. We conducted a retrosepctive consecutive single-center study, collecting personal and family cancer data of all BRCA1/2 patients referred to Cancer Genetics Departement of CHU Montpellier from 2003 to 2018. We reported 448 BRCA1/2 families, including 78 (17%) families with at least one VEO breast or ovarian cancer. Cumulative prevalence of VEO breast cancer was 5.09% (95%CI 3.61-6.58) in BRCA1 women and 2.47% (95%CI 1.37-3.56) in BRCA2. Cumulative prevalence of VEO ovarian cancer was 2.73% (95%CI 1.63-3.82) and 0.52% (95%CI 0.01-1.03) in BRCA1 and BRCA2 respectively. There was no significant relationship between VEO cancer occurrence and ages at cancer diagnosis within the family. VEO breast cancer frequency in BRCA1/2 women could prompt to implement MRI screening from age 25. Youngest age at diagnosis within a family was not confirmed to be a relevant factor for individualization of the age to start prevention.