Background: In the phase III IMpassion130 trial, combining atezolizumab with first-line nanoparticle albumin-boundpaclitaxel for advanced triple-negative breast cancer (aTNBC) showed a statistically significant progression-free survival (PFS) benefit in the intention-to-treat (ITT) and programmed death-ligand 1 (PD-L1)-positive populations, and a clinically meaningful overall survival (OS) effect in PD-L1-positive aTNBC. The phase III KEYNOTE-355 trial adding pembrolizumab to chemotherapy for aTNBC showed similar PFS effects. IMpassion131 evaluated first-line atezolizumabepaclitaxel in aTNBC. Patients and methods: Eligible patients [no prior systemic therapy or 12 months since (neo)adjuvant chemotherapy] were randomised 2:1 to atezolizumab 840 mg or placebo (days 1, 15), both with paclitaxel 90 mg/m 2 (days 1, 8, 15), every 28 days until disease progression or unacceptable toxicity. Stratification factors were tumour PD-L1 status, prior taxane, liver metastases and geographical region. The primary endpoint was investigator-assessed PFS, tested hierarchically first in the PD-L1-positive [immune cell expression 1%, VENTANA PD-L1 (SP142) assay] population, and then in the ITT population. OS was a secondary endpoint. Results: Of 651 randomised patients, 45% had PD-L1-positive aTNBC. At the primary PFS analysis, adding atezolizumab to paclitaxel did not improve investigator-assessed PFS in the PD-L1-positive population [hazard ratio (HR) 0.82, 95% confidence interval (CI) 0.60-1.12; P ¼ 0.20; median PFS 6.0 months with atezolizumabepaclitaxel versus 5.7 months with placeboepaclitaxel]. In the PD-L1-positive population, atezolizumabepaclitaxel was associated with more favourable unconfirmed best overall response rate (63% versus 55% with placeboepaclitaxel) and median duration of response (7.2 versus 5.5 months, respectively). Final OS results showed no difference between arms (HR 1.11, 95% CI 0.76-1.64; median 22.1 months with atezolizumabepaclitaxel versus 28.3 months with placeboe paclitaxel in the PD-L1-positive population). Results in the ITT population were consistent with the PD-L1-positive population. The safety profile was consistent with known effects of each study drug. Conclusion: Combining atezolizumab with paclitaxel did not improve PFS or OS versus paclitaxel alone. ClinicalTrials.gov: NCT03125902.

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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.

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