In OC patients with a gBRCA1 mutation with or without additional OC cases in the family, who did not have a family history of BC (from here onward referred to as “pure OC families”), the majority of mutations (17/24; 71%, 95% CI 51%‐85%) were positioned in a BRCA1 OCCR, while the remaining 29% (95% CI 15%‐49%) were located in non‐BRCA1 OCCR regions. This evidence concerns the gene BRCA1 and breast cancer.