Low- and Moderate-Penetrance Genes Associated With Breast and / or Ovarian Cancer
BRIP1 (also known as BACH1) encodes a helicase that interacts with the BRCT domain of BRCA1. This gene also has a role in BRCA1-dependent DNA repair and cell cycle checkpoint function. Biallelic mutations in BRIP1 are a cause of Fanconi anemia,[54,55,56] much like such mutations in BRCA2. Inactivating mutations of BRIP1 are associated with an increased risk of breast cancer. In one study, more than 3,000 individuals from BRCA1/BRCA2 mutation negative families were examined for BRIP1 mutations. Mutations were identified in 9 of 1,212 individuals with breast cancer but in only 2 of 2,081 controls (P = .003). The RR of breast cancer was estimated to be 2.0 (95% confidence interval [CI], 1.2–3.2; P = .012). Of note, in families with BRIP1 mutations and multiple cases of breast cancer, there was incomplete segregation of the mutation with breast cancer, consistent with a low penetrance allele and similar to that seen with CHEK2.
PALB2 (partner and localizer of BRCA2) interacts with the BRCA2 protein and plays a role in homologous recombination and double-stranded DNA repair. Similar to BRIP1 and BRCA2, biallelic mutations in PALB2 have also been shown to cause Fanconi anemia. PALB2 mutations have been screened for in multiple small studies of familial and early-onset breast cancer in multiple populations.[59,60,61,62,63,64,65,66,67,68,69,70,71] Mutation prevalence has ranged from 0.4% to 3.4%. Similar to BRIP1 and CHEK2, there was incomplete segregation of PALB2 mutations in families with hereditary breast cancer. Among 559 cases with contralateral breast cancer and 565 matched controls with unilateral breast cancer, pathogenic (truncating) PALB2 mutations were identified in 0.9% of cases and in none of the controls (RR, 5.3; 95% CI, 1.8–13.2). A Finnish PALB2 founder mutation (c.1592delT) has been reported to confer a 40% risk of breast cancer to age 70 years  and is associated with a high incidence (54%) of triple-negative disease and lower survival. Mutations have been observed in early-onset and familial breast cancer in many populations.[63,64]