Abstract P3-03-02: ER dependent breast cancer phenotype in BRCA 1/2 carriers

Abstract

Abstract Background: Hereditary breast cancer (HBC) comprises more than 10% of all breast cancers (BC). Mutations in the BRCA1/2 genes are found in approximately half of HBC patients. The majority of BRCA1 associated tumors are ER, PR and HER2 negative with basal-like expression pattern. BRCA2 associated tumors are mostly ER positive (ER+). In the present study we aim to further explore clinical and molecular characteristics of BRCA associated BC in 3 different cohorts. Methods: Three different BC databases (DB) were evaluated: (i) Hadassah oncogenetic BC DB (n=4429); (ii) Nick-Zainal et al. BC DB (n=560), and (iii) METABRIC BC DB (n= 1980). We tested for differences in age at diagnosis between BRCA positive (BRCA+) and BRCA negative (BRCA-) patients with either ER+ or ER negative (ER-) tumors. Point mutation analysis was performed in cohorts ii & iii and mRNA differential expression (DEA) and pathway analysis were performed in cohort iii, using Ingenuity Pathway Analysis (IPA). Results: Age (years) at diagnosis for cohorts i, ii,&iii respectively, for ER+ PT:BRCA1-44, NA, 60; for BRCA2-49, 48, 64; for BN – 53, 56, 63. For ER-: BRCA1-42, 42, 47; for BRCA2-48, 52, 49; for BN-49, 54, 56. For cohorts ii&iii, higher frequencies of TP53 and PIK3Ca mutations were found among BRCA+&BRCA-, respectively. DEA was performed between BRCA+&BRCA- in ER- tumors: the major activated pathways involved cancer related processes and were highly significant (up to p=1e-7.5, FDR=1e-4.5). Surprisingly - the most significant pathway was Estrogen Mediated S-phase Entry and the most activated upstream regulator was ERBB2. Similar evaluation in ER+ showed mostly differences in immune related pathways (differences not statistically significant). Conclusions: Younger age at presentation was observed in BRCA1 vs. BRCA2 patients. No age differences were observed between ER+&ER- PT in cohort i&ii, in cohort iii ER- BRCA+ Patients were younger than ER+ BRCA+ (similar age as ER+ BRCA-). BRCA+ show different mutational profile than BRCA-. ER+ BRCA+ and BRCA- show similar genomic characteristics. By contrast, for ER- BRCA+ differs markedly from BRCA-. This might imply that BRCA+ associated tumors consist of two genomically distinct subtypes: (i) ER-, and (ii) ER+. The results may shed light on possible somatic factors which affect the development of BC BRCA+ and carry preventive and therapeutic implications. Citation Format: Peretz TY, Zick A, Luna K, Grinshpun A, Sonneblick A, Iziely B, Hamburger TG, Cohen S, Granit AM, Dvir M, Rosenberg S. ER dependent breast cancer phenotype in BRCA 1/2 carriers [abstract]. In: Proceedings of the 2017 San Antonio Breast Cancer Symposium; 2017 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2018;78(4 Suppl):Abstract nr P3-03-02.