Spectrum and frequencies of BRCA1/2 mutations in Bulgarian high risk breast cancer patients.

Background: About 3885 women are diagnosed with breast cancer and 1285 die from the disease each year in Bulgaria. However no genetic testing to identify the mutations in high-risk families has been provided so far.
Methods: We evaluated 200 Bulgarian women with primary invasive breast cancer and with personal/ family history of breast cancer for the presence of unequivocally damaging germline mutations in BRCA1/2 using Sanger sequencing.
Results: Of the 200 patients, 39 (19.5 %) carried a disease predisposing mutation, including 28 (14 %) with a BRCA1 mutation and 11 (5.5 %) with a BRCA2 mutation. At BRCA1, 6 different mutations were identified, including 2 frameshifts, 1 nonsense and 1 missense that had been previously reported (c.5030_5033delCTAA, c.5263_5264insC, c.4603G > T, c.181 T > G), and 2 frameshifts, which were novel to this study (c.464delA, c.5397_5403delCCCTTGG). At BRCA2, 7 different frameshift mutations were identified, including 5 previously reported (5851_5854delAGTT, c.5946delT, c.5718_5719delCT, c.7910_7914delCCTTT,c.9098_9099insA) and 2 novel (c.8532_8533delAA, c.9682delA). A BRCA1 mutation was found in 18.4 % of women diagnosed with breast cancer at/or under the age of 40 compared to 11.2 % of women diagnosed at a later age; a BRCA2 mutation was found in 4 % of women diagnosed at/or under the age of 40 compared to 6.5 % of women diagnosed at a later age. A mutation was present in 26.8 % patients with a positive family history and in 14.4 % of women with a negative family history. The most prevalent mutation observed in 22 patients (11 %) was BRCA1 c.5263_5264insC, a known Slavic mutation with founder effect in Eastern European and AJ communities. Other recurrent mutations were BRCA2 c.9098-9099insA (2 %), BRCA1 c.181T > G (1 %) and BRCA2 c.5851_5854delAGTT (1 %). Notably, BRCA1 c.5263_5264insC represented 56 % of all mutations identified in this series. Of the 22 patients with BRCA1 c.5263_5264insC, 9 were diagnosed with early onset breast cancer, 11 with TNBCs, 4 with bilateral breast cancer, and 6 with both breast and ovarian cancer.
Conclusions: This is the first comprehensive study of the BRCA1/2 mutation spectrum in Bulgaria and will assist the establishment of efficient protocols for genetic testing and individualized risk assessment for Bulgarian breast/ovarian cancer patients and healthy individuals at a high-risk.