1)The prevalence of BRCA mutation carriers in the general population is estimated at between 1/800 and 1/1000. BRCA1 and BRCA2 mutation frequencies in breast and ovarian cancer patients unselected for family history or age at onset are generally low (<1–7% for BRCA1 and 1–3% for BRCA2). Higher prevalence is associated with a family history of breast or ovarian cancer, young age at onset, male breast cancer or multiple tumors (bilateral breast cancer or breast and ovarian cancer in the same patient).
https://academic.oup.com/annonc/article/20/suppl_4/iv19/147413/BRCA-in-breast-cancer-ESMO-Clinical
2)Mutations in BRCA1 and BRCA2 are estimated to account for 5% of all breast cancers and 50% of hereditary breast cancers (from https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4374018/)
