Characteristics of breast cancer in BRCA1/BRCA2 mutation carriers and non-carriersfrom a genetic counseling unit in Croatia

Breast cancer (BC) represents 25% of all malignancies in Croatian women, and in 18.8% of cases, it is diagnosed before the age of 50. Croatia launched BRCA testing of people at increased family risk. Hereditary BC is mainly caused by a pathogenic mutation in the BRCA1 or BRCA2 gene and is a significant risk factor for developing breast and ovarian cancer. The present study included 127 women diagnosed with BC, with a strong family history of BC and the known status of the germline mutations in the BRCA1/BRCA2 genes. The majority of women were BRCA1/2 mutation non-carriers, while 15.7% were BRCA1/2 mutation carriers, and 4% had a variant of unknown significance (VUS). BRCA1/2 mutation carriers were younger than non-carriers (median 38.5 years vs. 44 years) (P=.01) and had tumors of higher histological grade (P<.001). The intrinsic subtype of BC differs significantly depending on the type of mutation (P<.001). Triple-negative BC prevailed (87.5%) in BRCA1 mutation carriers, and 12.5% had a luminal B/HER2-negative BC. Four patients were BRCA2 mutation carriers, and two of them had luminal B/HER2-positive BC. Most BRCA1/2 non-carriers (69.2%) and all VUS-carriers have luminal B/HER2-negative BC. Our results show that BRCA1/2 mutation testing is essential for women with a family history burden. It is a piece of valuable information in breast cancer risk assessment and contributes to early diagnosis.