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Objectives: The value of a high-risk surveillance program for mutation carriers and women at high familial breast cancer risk has not been extensively studied. A Breast and Ovarian Cancer Risk Management Clinic (BOCRMC) was established at the Royal Melbourne Hospital in 2010 to provide multimodality screening and risk management strategies for this group of women. The aims of this study were to evaluate the program and describe breast cancer diagnoses for BRCA1, BRCA2, and other germline mutation carriers as well as high-risk noncarriers attending the BOCRMC., Methods: Clinical data from mutation carriers and noncarriers with a ≥25% lifetime risk of developing breast cancer who attended between 2010 and 2018 were extracted from clinic records and compared. The pattern and mode of detection of cancer were determined., Results: A total of 206 mutation carriers and 305 noncarriers attended the BOCRMC and underwent screening on at least one occasion. Median age was 37 years. After a median follow-up of 34 months, 15 (seven invasive) breast cancers were identified in mutation carriers, with seven (six invasive) breast cancers identified in noncarriers. Of these, 20 (90.9%) were detected by annual screening, whereas two (9.1%) were detected as interval cancers (both in BRCA1 mutation carriers). Median size of the invasive breast cancers was 11 mm (range: 1.5-30 mm). The majority (76.9%) were axillary node negative. In women aged 25-49 years, the annualized cancer incidence was 1.6% in BRCA1, 1.4% in BRCA2 mutation carriers, and 0.5% in noncarriers. This compares to 0.06% annualized cancer incidence in the general Australian population., Conclusions: Screening was effective at detecting early-stage cancers. The incidence of events in young noncarriers was substantially higher than in the general population. This potentially justifies ongoing management through a specialty clinic, although further research to better personalize risk assessment in noncarriers is required., (© 2019 John Wiley & Sons Australia, Ltd.)

The mammary gland is a highly dynamic organ that undergoes profound changes within its epithelium during puberty and the reproductive cycle. These changes are fueled by dedicated stem and progenitor cells. Both short- and long-lived lineage-restricted progenitors have been identified in adult tissue as well as a small pool of multipotent mammary stem cells (MaSCs), reflecting intrinsic complexity within the epithelial hierarchy. While unipotent progenitor cells predominantly execute day-to-day homeostasis and postnatal morphogenesis during puberty and pregnancy, multipotent MaSCs have been implicated in coordinating alveologenesis and long-term ductal maintenance. Nonetheless, the multipotency of stem cells in the adult remains controversial. The advent of large-scale single-cell molecular profiling has revealed striking changes in the gene expression landscape through ontogeny and the presence of transient intermediate populations. An increasing number of lineage cell-fate determination factors and potential niche regulators have now been mapped along the hierarchy, with many implicated in breast carcinogenesis. The emerging diversity among stem and progenitor populations of the mammary epithelium is likely to underpin the heterogeneity that characterizes breast cancer.

Background: Mutations in BRCA2 cause a higher risk of early-onset aggressive prostate cancer (PrCa). The IMPACT study is evaluating targeted PrCa screening using prostate-specific-antigen (PSA) in men with germline BRCA1/2 mutations., Objective: To report the utility of PSA screening, PrCa incidence, positive predictive value of PSA, biopsy, and tumour characteristics after 3 yr of screening, by BRCA status., Design, Setting, and Participants: Men aged 40-69 yr with a germline pathogenic BRCA1/2 mutation and male controls testing negative for a familial BRCA1/2 mutation were recruited. Participants underwent PSA screening for 3 yr, and if PSA > 3.0 ng/ml, men were offered prostate biopsy., Outcome Measurements and Statistical Analysis: PSA levels, PrCa incidence, and tumour characteristics were evaluated. Statistical analyses included Poisson regression offset by person-year follow-up, chi-square tests for proportion t tests for means, and Kruskal-Wallis for medians., Results and Limitations: A total of 3027 patients (2932 unique individuals) were recruited (919 BRCA1 carriers, 709 BRCA1 noncarriers, 902 BRCA2 carriers, and 497 BRCA2 noncarriers). After 3 yr of screening, 527 men had PSA > 3.0 ng/ml, 357 biopsies were performed, and 112 PrCa cases were diagnosed (31 BRCA1 carriers, 19 BRCA1 noncarriers, 47 BRCA2 carriers, and 15 BRCA2 noncarriers). Higher compliance with biopsy was observed in BRCA2 carriers compared with noncarriers (73% vs 60%). Cancer incidence rate per 1000 person years was higher in BRCA2 carriers than in noncarriers (19.4 vs 12.0; p =  0.03); BRCA2 carriers were diagnosed at a younger age (61 vs 64 yr; p =  0.04) and were more likely to have clinically significant disease than BRCA2 noncarriers (77% vs 40%; p =  0.01). No differences in age or tumour characteristics were detected between BRCA1 carriers and BRCA1 noncarriers. The 4 kallikrein marker model discriminated better (area under the curve [AUC] = 0.73) for clinically significant cancer at biopsy than PSA alone (AUC = 0.65)., Conclusions: After 3 yr of screening, compared with noncarriers, BRCA2 mutation carriers were associated with a higher incidence of PrCa, younger age of diagnosis, and clinically significant tumours. Therefore, systematic PSA screening is indicated for men with a BRCA2 mutation. Further follow-up is required to assess the role of screening in BRCA1 mutation carriers., Patient Summary: We demonstrate that after 3 yr of prostate-specific antigen (PSA) testing, we detect more serious prostate cancers in men with BRCA2 mutations than in those without these mutations. We recommend that male BRCA2 carriers are offered systematic PSA screening., (Copyright © 2019 The Authors. Published by Elsevier B.V. All rights reserved.)

The aim of this study was to retrospectively describe the genetic testing motives and experiences of women with a previous breast and/or ovarian cancer diagnosis, who received negative BRCA1/2 results including variants of unknown significance and no pathogenic variant detected. One hundred and thirteen women (mean age 56.17 years) were recruited from a familial cancer centre in metropolitan Australia, an average 3.4 years after undergoing testing. Participants completed a self-report questionnaire focusing on the retrospective experience of and motives for undergoing BRCA1/2 testing. The study found that the primary motives for undergoing BRCA1/2 testing were (a) to know more about whether their cancer was hereditary, and (b) to have more certainty about the risk of their children developing cancer. In terms of perceptions of personal risk, 35% of women perceived that their risk of breast cancer to be the same or lower than the general population and 80% believed the negative test result to mean that a risk-conferring gene had not been detected. Yet, the average estimate of the likelihood that their cancer was hereditary was 48 out of a possible 100. Psychologically, women did not interpret the negative BRCA1/2 result as a positive outcome. Half were not relieved by the result and were as or more worried than before. Psychological morbidity was high with 17%, 100%, and 36% experiencing clinically significant depression, anxiety, and cancer-specific distress, respectively. Self-ratings of the likelihood that their cancer was hereditary were more closely associated with their personal family cancer histories than with measures of psychological distress. These results have implications for adherence to risk-reducing behaviours and quality of life. Given that these women are not routinely followed up in clinical practice, these findings highlight the importance of post-test genetic counselling and longer-term follow-up for women with negative BRCA1/2 results. Additional time and emotional support from genetic counsellors may help this group of women make sense of the meaning of their test result and adjust psychologically, particularly to uncertainty around the cause of their family history.

Purpose: Metastatic triple-negative breast cancer (TNBC) is a phenotypic breast cancer subgroup with a very poor prognosis, despite standard treatments. Combined twice-weekly iniparib and gemcitabine/carboplatin (GC+tw-iniparib) showed benefit over gemcitabine/carboplatin in a randomized phase II trial, and a phase III was initiated comparing these regimens. The present phase II study was initiated to compare GC+tw-iniparib with a more practical once-weekly schedule (GC+w-iniparib) in TNBC., Methods: Metastatic TNBC patients were randomized to receive iniparib weekly (11.2 mg/kg on days 1 and 8) or twice-weekly (5.6 mg/kg on days 1, 4, 8, and 11) with gemcitabine (1000 mg/m 2 ) and carboplatin (area under the curve 2 on days 1 and 8), every 3 weeks. The primary endpoint was the overall response rate (ORR). Pharmacokinetics of iniparib and its two metabolites were analyzed., Results: A total of 163 patients were randomized, 82 GC+w-iniparib and 81 GC+tw-iniparib. Demographic and baseline characteristics were well balanced. ORR was 34.1% (95% CI 23.9-44.4%) vs. 29.6% (95% CI 19.7-39.6%) and median progression-free survival was 5.5 months (95% CI 4.2-5.7) vs. 4.3 months (95% CI 3.0-5.8) for GC+w-iniparib and GC+tw-iniparib, respectively. Safety was similar across treatment arms in terms of event severity and type. Iniparib plasma concentrations and exposure were two-fold higher with w-iniparib compared to tw-iniparib. Iniparib and its metabolites were cleared rapidly with a terminal half-life of < 1 h, without accumulation., Conclusions: Despite a doubled maximum concentration with weekly iniparib, no detectable differences in safety or efficacy were observed between the weekly and twice-weekly administration schedules in this population., Trial Registration: ClinicalTrial.gov Identifier NCT01045304.

Venetoclax, a potent and selective BCL2 inhibitor, synergizes with endocrine therapy in preclinical models of ER-positive breast cancer. Using a phase Ib 3 + 3 dose-escalation and expansion study design, 33 patients with ER and BCL2-positive metastatic disease (mean prior regimens, 2; range, 0-8) were treated with daily tamoxifen (20 mg) and venetoclax (200-800 mg). Apart from uncomplicated "on-target" lymphopenia, no dose-limiting toxicities or high-grade adverse events were observed in the escalation phase (15 patients), and 800 mg was selected as the recommended phase II dose (RP2D). In the expansion phase (18 patients), few high-grade treatment-related adverse events were observed. For 24 patients treated at the RP2D, the confirmed radiologic response rate was 54% and the clinical benefit rate was 75%. Treatment responses were preempted by metabolic responses (FDG-PET) at 4 weeks and correlated with serial changes in circulating tumor DNA. Radiologic responses (40%) and clinical benefit (70%) were observed in 10 patients with plasma-detected ESR1 mutations. SIGNIFICANCE: In the first clinical study to evaluate venetoclax in a solid tumor, we demonstrate that combining venetoclax with endocrine therapy has a tolerable safety profile and elicits notable activity in ER and BCL2-positive metastatic breast cancer. These findings support further investigation of combination therapy for patients with BCL2-positive tumors. See related commentary by Drago et al., p. 323 . This article is highlighted in the In This Issue feature, p. 305 ., (©2018 American Association for Cancer Research.)

Primary triple negative breast cancers (TNBC) are prone to dissemination but sub-clonal relationships between tumors and resulting metastases are poorly understood. Here we use cellular barcoding of two treatment-naïve TNBC patient-derived xenografts (PDXs) to track the spatio-temporal fate of thousands of barcoded clones in primary tumors, and their metastases. Tumor resection had a major impact on reducing clonal diversity in secondary sites, indicating that most disseminated tumor cells lacked the capacity to 'seed', hence originated from 'shedders' that did not persist. The few clones that continued to grow after resection i.e. 'seeders', did not correlate in frequency with their parental clones in primary tumors. Cisplatin treatment of one BRCA1-mutated PDX model to non-palpable levels had a surprisingly minor impact on clonal diversity in the relapsed tumor yet purged 50% of distal clones. Therefore, clonal features of shedding, seeding and drug resistance are important factors to consider for the design of therapeutic strategies.

Background: We conducted a Phase 1 study to evaluate safety and activity of olaparib tablets and oral cyclophosphamide., Methods: Patients had metastatic breast cancer (BC) or recurrent high-grade serous ovarian cancer (HGSOC), performance status 0-2, and ≤3 lines of prior therapy. Patients were treated using a dose escalation strategy with cohort expansion once maximal tolerated dose (MTD) was determined. Dose level 1 (DL1): olaparib 300 mg bid, cyclophosphamide 50 mg on days 1, 3, and 5, weekly. DL2: olaparib 300 mg bid, cyclophosphamide 50 mg, days 1-5 weekly., Results: Of 32 patients, 23 had HGSOC (germline BRCA mutation [gBRCAm] 70%) and 9 had BC (gBRCAm 67%). Four were treated at DL1 and 28 at DL2, the MTD. Haematological adverse events (AEs) were most common: grade 3/4 AEs: lymphopenia 75%, anaemia 31%, neutropenia 37%, thrombocytopenia 47%. Two permanently discontinued treatment due to haematological AEs. In BC, no objective response was reported. Unconfirmed objective response was 48% and 64% for all HGSOC and gBRCAm subset, respectively. CA125 responses were 70% (all HGSOC) and 92% (gBRCAm)., Conclusions: In HGSOC and BC, olaparib 300 mg bid and cyclophosphamide 50 mg on days 1-5 weekly were tolerable and active, particularly in gBRCAm, and is worthy of further investigation.

BRCA1-mutated breast cancer is primarily driven by DNA copy-number alterations (CNAs) containing large numbers of candidate driver genes. Validation of these candidates requires novel approaches for high-throughput in vivo perturbation of gene function. Here we develop genetically engineered mouse models (GEMMs) of BRCA1-deficient breast cancer that permit rapid introduction of putative drivers by either retargeting of GEMM-derived embryonic stem cells, lentivirus-mediated somatic overexpression or in situ CRISPR/Cas9-mediated gene disruption. We use these approaches to validate Myc, Met, Pten and Rb1 as bona fide drivers in BRCA1-associated mammary tumorigenesis. Iterative mouse modeling and comparative oncogenomics analysis show that MYC-overexpression strongly reshapes the CNA landscape of BRCA1-deficient mammary tumors and identify MCL1 as a collaborating driver in these tumors. Moreover, MCL1 inhibition potentiates the in vivo efficacy of PARP inhibition (PARPi), underscoring the therapeutic potential of this combination for treatment of BRCA1-mutated cancer patients with poor response to PARPi monotherapy.

Long-lived quiescent mammary stem cells (MaSCs) are presumed to coordinate the dramatic expansion of ductal epithelium that occurs through the different phases of postnatal development, but little is known about the molecular regulators that underpin their activation. We show that ablation of the transcription factor Foxp1 in the mammary gland profoundly impairs ductal morphogenesis, resulting in a rudimentary tree throughout life. Foxp1-deficient glands were highly enriched for quiescent Tspan8 hi MaSCs, which failed to become activated even in competitive transplantation assays, thus highlighting a cell-intrinsic defect. Foxp1 deletion also resulted in aberrant expression of basal genes in luminal cells, inferring a role in cell-fate decisions. Notably, Foxp1 was uncovered as a direct repressor of Tspan8 in basal cells, and deletion of Tspan8 rescued the defects in ductal morphogenesis elicited by Foxp1 loss. Thus, a single transcriptional regulator Foxp1 can control the exit of MaSCs from dormancy to orchestrate differentiation and development., (Copyright © 2018 Elsevier Inc. All rights reserved.)

Distinct transcriptional states are maintained through organization of chromatin, resulting from the sum of numerous repressive and active histone modifications, into tightly packaged heterochromatin versus more accessible euchromatin. Polycomb repressive complex 2 (PRC2) is the main mammalian complex responsible for histone 3 lysine 27 trimethylation (H3K27me3) and is integral to chromatin organization. Using in vitro and in vivo studies, we show that deletion of Suz12, a core component of all PRC2 complexes, results in loss of H3K27me3 and H3K27 dimethylation (H3K27me2), completely blocks normal mammary gland development, and profoundly curtails progenitor activity in 3D organoid cultures. Through the application of mammary organoids to bypass the severe phenotype associated with Suz12 loss in vivo, we have explored gene expression and chromatin structure in wild-type and Suz12-deleted basal-derived organoids. Analysis of organoids led to the identification of lineage-specific changes in gene expression and chromatin structure, inferring cell type-specific PRC2-mediated gene silencing of the chromatin state. These expression changes were accompanied by cell cycle arrest but not lineage infidelity. Together, these data indicate that canonical PRC2 function is essential for development of the mammary gland through the repression of alternate transcription programs and maintenance of chromatin states., Competing Interests: The authors have declared that no competing interests exist.

This corrects the article DOI: 10.1038/bjc.2017.429.

The Oncotype DX ® assay was developed to address the need for optimizing the selection of adjuvant systemic therapy for patients with estrogen receptor (ER)-positive, lymph node-negative breast cancer. It has ushered in the era of genomic-based personalized cancer care for ER-positive primary breast cancer and is now widely utilized in various parts of the world. Together with several other genomic assays, Oncotype DX has been incorporated into clinical practice guidelines on biomarker use to guide treatment decisions. The Oncotype DX result is presented as the recurrence score which is a continuous score that predicts the risk of distant disease recurrence. The assay, which provides information on clinicopathological factors, has been validated for use in the prognostication and prediction of degree of adjuvant chemotherapy benefit in both lymph node-positive and lymph node-negative early breast cancers. Clinical studies have consistently shown that the Oncotype DX has a significant impact on decision making in adjuvant therapy recommendations and appears to be cost-effective in diverse health care settings. In this article, we provide an overview of the validation and clinical impact studies for the Oncotype DX assay. We also discuss its potential use in the neoadjuvant setting, as well as the more recent prospective validation trials, and the economic and utility implications of studies that use a lower cutoff score to define low-risk disease., Competing Interests: Disclosure The authors report no conflicts of interest in this work.

The mammary epithelium comprises two primary cellular lineages, but the degree of heterogeneity within these compartments and their lineage relationships during development remain an open question. Here we report single-cell RNA profiling of mouse mammary epithelial cells spanning four developmental stages in the post-natal gland. Notably, the epithelium undergoes a large-scale shift in gene expression from a relatively homogeneous basal-like program in pre-puberty to distinct lineage-restricted programs in puberty. Interrogation of single-cell transcriptomes reveals different levels of diversity within the luminal and basal compartments, and identifies an early progenitor subset marked by CD55. Moreover, we uncover a luminal transit population and a rare mixed-lineage cluster amongst basal cells in the adult mammary gland. Together these findings point to a developmental hierarchy in which a basal-like gene expression program prevails in the early post-natal gland prior to the specification of distinct lineage signatures, and the presence of cellular intermediates that may serve as transit or lineage-primed cells.

Purpose: Unaffected women who carry BRCA1 or BRCA2 mutations face difficult choices about reducing their breast cancer risk. Understanding their treatment preferences could help us improve patient counseling and inform drug trials. The objective was to explore preferences for various risk-reducing options among women with germline BRCA1/2 mutations using a discrete-choice experiment survey and to compare expressed preferences with actual behaviors., Methods: A discrete-choice experiment survey was designed wherein women choose between hypothetical treatments to reduce breast cancer risk. The hypothetical treatments were characterized by the extent of breast cancer risk reduction, treatment duration, impact on fertility, hormone levels, risk of uterine cancer, and ease and mode of administration. Data were analyzed using a random-parameters logit model. Women were also asked to express their preference between surgical and chemoprevention options and to report on their actual risk-reduction actions. Women aged 25-55 years with germline BRCA1/2 mutations who were unaffected with breast or ovarian cancer were recruited through research registries at five clinics and a patient advocacy group., Results: Between January 2015 and March 2016, 622 women completed the survey. Breast cancer risk reduction was the most important consideration expressed, followed by maintaining fertility. Among the subset of women who wished to have children in future, the ability to maintain fertility was the most important factor, followed by the extent of risk reduction. Many more women said they would take a chemoprevention drug than had actually taken chemoprevention., Conclusions: Women with BRCA1/2 mutations indicated strong preferences for breast cancer risk reduction and maintaining fertility. The expressed desire to have a safe chemoprevention drug available to them was not met by current chemoprevention options.

The development of BH3 mimetics, which antagonize prosurvival proteins of the BCL-2 family, represents a potential breakthrough in cancer therapy. Targeting the prosurvival member MCL-1 has been an area of intense interest because it is frequently deregulated in cancer. In breast cancer, MCL-1 is often amplified, and high expression predicts poor patient outcome. We tested the MCL-1 inhibitor S63845 in breast cancer cell lines and patient-derived xenografts with high expression of MCL-1. S63845 displayed synergistic activity with docetaxel in triple-negative breast cancer and with trastuzumab or lapatinib in HER2-amplified breast cancer. Using S63845-resistant cells combined with CRISPR (clustered regularly interspaced short palindromic repeats)-Cas9 (CRISPR-associated 9) technology, we identified deletion of BAK and up-regulation of prosurvival proteins as potential mechanisms that confer resistance to S63845 in breast cancer. Collectively, our findings provide a strong rationale for the clinical evaluation of MCL-1 inhibitors in breast cancer., (Copyright © 2017 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works.)

Immune checkpoint inhibitors have emerged as a potent new class of anticancer therapy. They have changed the treatment landscape for a range of tumors, particularly those with a high mutational load. To date, however, modest results have been observed in breast cancer, where tumors are rarely hypermutated. Because BRCA1 -associated tumors frequently exhibit a triple-negative phenotype with extensive lymphocyte infiltration, we explored their mutational load, immune profile, and response to checkpoint inhibition in a Brca1 -deficient tumor model. BRCA1 -mutated triple-negative breast cancers (TNBCs) exhibited an increased somatic mutational load and greater numbers of tumor-infiltrating lymphocytes, with increased expression of immunomodulatory genes including PDCD1 ( PD-1 ) and CTLA4 , when compared to TNBCs from BRCA1 -wild-type patients. Cisplatin treatment combined with dual anti-programmed death-1 and anti-cytotoxic T lymphocyte-associated antigen 4 therapy substantially augmented antitumor immunity in Brca1 -deficient mice, resulting in an avid systemic and intratumoral immune response. This response involved enhanced dendritic cell activation, reduced suppressive FOXP3 + regulatory T cells, and concomitant increase in the activation of tumor-infiltrating cytotoxic CD8 + and CD4 + T cells, characterized by the induction of polyfunctional cytokine-producing T cells. Dual (but not single) checkpoint blockade together with cisplatin profoundly attenuated the growth of Brca1 -deficient tumors in vivo and improved survival. These findings provide a rationale for clinical studies of combined immune checkpoint blockade in BRCA1 -associated TNBC., (Copyright © 2017, American Association for the Advancement of Science.)

Objective: Owing to the rapid increase in clinical need, we aimed to implement and review the performance of a mainstreaming model of germline BRCA1/2 genetic testing in eligible women with high grade non-mucinous epithelial ovarian cancer via a Genetic Counselor embedded in the gynecology oncology clinic., Methods: The model implemented involved a specialized referral form, weekly genetics-lead multidisciplinary review of referrals, and pre- and post-test genetic counseling provided by an embedded genetic counselor during chemotherapy chair time. Performance and outcomes were retrospectively audited over the following two consecutive one year periods, including survey data on medical specialist comfort with mainstreaming and the model., Results: Sixty-four women underwent mainstreamed BRCA1/2 testing over the two year post-implementation period with a rate of detection of BRCA1/2 pathogenic variants of 17%. The referral rate for eligible women significantly increased to over 90% (p<0.001). The median time from referral to delivery of genetic testing results was less than five months, with >90% of patients receiving results during first line chemotherapy. Genetic counseling time decreased from 120 to 54min. Cancer specialists were comfortable with the model., Conclusions: The mainstreaming model proved effective, increasing uptake of genetic testing in eligible patients to over 90%; it was efficient for patients, genetic counselors and cancer specialists and acceptable to cancer specialists. It facilitated co-location of genetic and oncology service delivery but separation of clinical responsibility for genetic testing to a specialist genetics service, ensuring accurate and robust patient-centred care., (Copyright © 2017 Elsevier Inc. All rights reserved.)

Aims: To assess the eligibility, uptake and impediments to tamoxifen use in high-risk women attending a risk management clinic due to family history., Patients and Methods: All patients with a germline mutation in a cancer predisposing gene or at high genetic risk (based on family history) attending a Breast and Ovarian cancer risk management clinic from February 2014 to May 2015 received both verbal and written evidence-based information on preventive therapy and were recommended to consider endocrine prevention if not contraindicated. Endocrine therapy initiation, use and cessation were captured. Patient eligibility was analysed and reasons for declining, ceasing or contraindications for medication use were recorded., Results: During the study period, 237 women were seen over 305 consultations for breast surveillance and preventative therapy discussion. They comprised 38 BRCA1 and 42 BRCA2 mutation carriers, 4 with Peutz-Jegher syndrome, 153 with a strong family history. Their median age was 39.4 years. Endocrine preventative was considered and discussed with all but 19 women. Of the remaining 218, 34 chose bilateral prophylactic mastectomy, while endocrine preventative was not recommended in 50 women due to contraindications and 25 women declined treatment due to their intention to fall pregnant. In 118 patients who remained eligible, 18.6% (22) tried prevention and 9.4% (14) remained on therapy., Conclusions: Physician-reluctance is not a dominant reason for poor uptake of endocrine prevention even by high-risk premenopausal women in a specialised risk management clinic. Many women are not eligible, and most elect for alternative options., (Copyright © 2017 Elsevier Ltd. All rights reserved.)

Advances in stem cell research have enabled the generation of 'mini organs' or organoids that recapitulate phenotypic traits of the original biological specimen. Although organoids have been demonstrated for multiple organ systems, there are more limited options for studying mouse mammary gland formation in vitro Here, we have built upon previously described culture assays to define culture conditions that enable the efficient generation of clonal organoid structures from single sorted basal mammary epithelial cells (MECs). Analysis of Confetti-reporter mice revealed the formation of uni-colored structures and thus the clonal nature of these organoids. High-resolution 3D imaging demonstrated that basal cell-derived complex organoids comprised an inner compartment of polarized luminal cells with milk-producing capacity and an outer network of elongated myoepithelial cells. Conversely, structures generated from luminal MECs rarely contained basal/myoepithelial cells. Moreover, flow cytometry and 3D microscopy of organoids generated from lineage-specific reporter mice established the bipotent capacity of basal cells and the restricted potential of luminal cells. In summary, we describe optimized in vitro conditions for the efficient generation of mouse mammary organoids that recapitulate features of mammary tissue architecture and function, and can be applied to understand tissue dynamics and cell-fate decisions., (© 2017. Published by The Company of Biologists Ltd.)

Despite accumulating evidence for a mammary differentiation hierarchy, the basal compartment comprising stem cells remains poorly characterized. Through gene expression profiling of Lgr5 + basal epithelial cells, we identify a new marker, Tetraspanin8 (Tspan8). Fractionation based on Tspan8 and Lgr5 expression uncovered three distinct mammary stem cell (MaSC) subsets in the adult mammary gland. These exist in a largely quiescent state but differ in their reconstituting ability, spatial localization, and their molecular and epigenetic signatures. Interestingly, the deeply quiescent MaSC subset (Lgr5 + Tspan8 hi ) resides within the proximal region throughout life, and has a transcriptome strikingly similar to that of claudin-low tumours. Lgr5 + Tspan8 hi cells appear to originate from the embryonic mammary primordia before switching to a quiescent state postnatally but can be activated by ovarian hormones. Our findings reveal an unexpected degree of complexity within the adult MaSC compartment and identify a dormant subset poised for activation in response to physiological stimuli.

The study and application of human pluripotent stem cells (hPSCs) will be enhanced by the availability of well-characterized monoclonal antibodies (mAbs) detecting cell-surface epitopes. Here, we report generation of seven new mAbs that detect cell surface proteins present on live and fixed human ES cells (hESCs) and human iPS cells (hiPSCs), confirming our previous prediction that these proteins were present on the cell surface of hPSCs. The mAbs all show a high correlation with POU5F1 (OCT4) expression and other hPSC surface markers (TRA-160 and SSEA-4) in hPSC cultures and detect rare OCT4 positive cells in differentiated cell cultures. These mAbs are immunoreactive to cell surface protein epitopes on both primed and naive state hPSCs, providing useful research tools to investigate the cellular mechanisms underlying human pluripotency and states of cellular reprogramming. In addition, we report that subsets of the seven new mAbs are also immunoreactive to human bone marrow-derived mesenchymal stem cells (MSCs), normal human breast subsets and both normal and tumorigenic colorectal cell populations. The mAbs reported here should accelerate the investigation of the nature of pluripotency, and enable development of robust cell separation and tracing technologies to enrich or deplete for hPSCs and other human stem and somatic cell types. Stem Cells 2017;35:626-640., (© 2016 The Authors Stem Cells published by Wiley Periodicals, Inc. on behalf of AlphaMed Press.)

Beyond prophylactic mastectomy, there are currently very few options available to BRCA1 mutation carriers to help reduce their risk of developing breast cancer. An effective prevention therapy therefore remains a pressing area of need. Accumulating evidence points to amplification of the progesterone signaling axis in precancerous tissue from BRCA1 mutation carriers. Given that RANKL is an important paracrine mediator of hormonal signaling in breast tissue, there has been considerable interest in exploring a potential role for this pathway in oncogenesis. Recent findings indicate that the RANK and NF-κB pathways are aberrantly activated in luminal progenitor cells resident in preneoplastic BRCA1 mut/+ breast tissue. The augmented proliferation of these cells and their predilection for DNA damage suggest that they are prime cellular targets for basal-like cancers arising in BRCA1 mutation carriers. The end result is a hyperactive pathway, initiated by progesterone and amplified by DNA damage-induced NF-κB signaling, that likely accounts for the susceptibility of BRCA1 mut/+ luminal progenitor cells to oncogenesis and tissue specificity. Specific targeting of this progenitor subset has revealed a compelling new prevention strategy for these and possibly other high-risk women. Cancer Res; 77(3); 595-600. ©2017 AACR., (©2017 American Association for Cancer Research.)

Patient-derived xenograft (PDX) models of a growing spectrum of cancers are rapidly supplanting long-established traditional cell lines as preferred models for conducting basic and translational preclinical research. In breast cancer, to complement the now curated collection of approximately 45 long-established human breast cancer cell lines, a newly formed consortium of academic laboratories, currently from Europe, Australia, and North America, herein summarizes data on over 500 stably transplantable PDX models representing all three clinical subtypes of breast cancer (ER+, HER2+, and "Triple-negative" (TNBC)). Many of these models are well-characterized with respect to genomic, transcriptomic, and proteomic features, metastatic behavior, and treatment response to a variety of standard-of-care and experimental therapeutics. These stably transplantable PDX lines are generally available for dissemination to laboratories conducting translational research, and contact information for each collection is provided. This review summarizes current experiences related to PDX generation across participating groups, efforts to develop data standards for annotation and dissemination of patient clinical information that does not compromise patient privacy, efforts to develop complementary data standards for annotation of PDX characteristics and biology, and progress toward "credentialing" of PDX models as surrogates to represent individual patients for use in preclinical and co-clinical translational research. In addition, this review highlights important unresolved questions, as well as current limitations, that have hampered more efficient generation of PDX lines and more rapid adoption of PDX use in translational breast cancer research.

Individuals who have mutations in the breast-cancer-susceptibility gene BRCA1 (hereafter referred to as BRCA1-mutation carriers) frequently undergo prophylactic mastectomy to minimize their risk of breast cancer. The identification of an effective prevention therapy therefore remains a 'holy grail' for the field. Precancerous BRCA1(mut/+) tissue harbors an aberrant population of luminal progenitor cells, and deregulated progesterone signaling has been implicated in BRCA1-associated oncogenesis. Coupled with the findings that tumor necrosis factor superfamily member 11 (TNFSF11; also known as RANKL) is a key paracrine effector of progesterone signaling and that RANKL and its receptor TNFRSF11A (also known as RANK) contribute to mammary tumorigenesis, we investigated a role for this pathway in the pre-neoplastic phase of BRCA1-mutation carriers. We identified two subsets of luminal progenitors (RANK(+) and RANK(-)) in histologically normal tissue of BRCA1-mutation carriers and showed that RANK(+) cells are highly proliferative, have grossly aberrant DNA repair and bear a molecular signature similar to that of basal-like breast cancer. These data suggest that RANK(+) and not RANK(-) progenitors are a key target population in these women. Inhibition of RANKL signaling by treatment with denosumab in three-dimensional breast organoids derived from pre-neoplastic BRCA1(mut/+) tissue attenuated progesterone-induced proliferation. Notably, proliferation was markedly reduced in breast biopsies from BRCA1-mutation carriers who were treated with denosumab. Furthermore, inhibition of RANKL in a Brca1-deficient mouse model substantially curtailed mammary tumorigenesis. Taken together, these findings identify a targetable pathway in a putative cell-of-origin population in BRCA1-mutation carriers and implicate RANKL blockade as a promising strategy in the prevention of breast cancer.

The mammary gland represents a unique tissue to study organogenesis as it predominantly develops in the post-natal animal and undergoes dramatic morphogenetic changes during puberty and the reproductive cycle. The physiological function of the mammary gland is to produce milk to sustain the newborn. Here we view the lactating gland through three-dimensional confocal imaging of intact tissue. We observed that the majority of secretory alveolar cells are binucleated. These cells first arise in very late pregnancy due to failure of cytokinesis and are larger than mononucleated cells. Augmented expression of Aurora kinase-A and Polo-like kinase-1 at the lactogenic switch likely mediates the formation of binucleated cells. Our findings demonstrate an important physiological role for polyploid mammary epithelial cells in lactation, and based on their presence in five different species, suggest that binucleated cells evolved to maximize milk production and promote the survival of offspring across all mammalian species.

The last three decades have seen significant progress in our understanding of the role of the pro-survival protein BCL-2 and its family members in apoptosis and cancer. BCL-2 and other pro-survival family members including Mcl-1 and BCL-XL have been shown to have a key role in keeping pro-apoptotic 'effector' proteins BAK and BAX in check. They also neutralize a group of 'sensor' proteins (such as BIM), which are triggered by cytotoxic stimuli such as chemotherapy. BCL-2 proteins therefore have a central role as guardians against apoptosis, helping cancer cells to evade cell death. More recently, an increasing number of BH3 mimetics, which bind and neutralize BCL-2 and/or its pro-survival relatives, have been developed. The utility of targeting BCL-2 in hematological malignancies has become evident in early-phase studies, with remarkable clinical responses seen in heavily pretreated patients. As BCL-2 is overexpressed in ~75% of breast cancer, there has been growing interest in determining whether this new class of drug could show similar promise in breast cancer. This review summarizes our current understanding of the role of BCL-2 and its family members in mammary gland development and breast cancer, recent progress in the development of new BH3 mimetics as well as their potential for targeting estrogen receptor-positive breast cancer.

Evasion of cell death is fundamental to the development of cancer and its metastasis. The role of the BCL-2-mediated (intrinsic) apoptotic program in these processes remains poorly understood. Here we have investigated the relevance of the pro-apoptotic protein BIM to breast cancer progression using the MMTV-Polyoma middle-T (PyMT) transgenic model. BIM deficiency in PyMT females did not affect primary tumor growth, but substantially increased the survival of metastatic cells within the lung. These data reveal a role for BIM in the suppression of breast cancer metastasis. Intriguingly, we observed a striking correlation between the expression of BIM and the epithelial to mesenchymal transition transcription factor SNAI2 at the proliferative edge of the tumors. Overexpression and knockdown studies confirmed that these two genes were coordinately expressed, and chromatin immunoprecipitation analysis further revealed that Bim is a target of SNAI2. Taken together, our findings suggest that SNAI2-driven BIM-induced apoptosis may temper metastasis by governing the survival of disseminating breast tumor cells.

Introduction: MicroRNAs (miRNAs) have been implicated in governing lineage specification and differentiation in multiple organs; however, little is known about their specific roles in mammopoiesis. We have determined the global miRNA expression profiles of functionally distinct epithelial subpopulations in mouse and human mammary tissue, and compared these to their cognate transcriptomes and epigenomes. Finally, the human miRNA signatures were used to interrogate the different subtypes of breast cancer, with a view to determining miRNA networks deregulated during oncogenesis., Methods: RNA from sorted mouse and human mammary cell subpopulations was subjected to miRNA expression analysis using the TaqMan MicroRNA Array. Differentially expressed (DE) miRNAs were correlated with gene expression and histone methylation profiles. Analysis of miRNA signatures of the intrinsic subtypes of breast cancer in The Cancer Genome Atlas (TCGA) database versus those of normal human epithelial subpopulations was performed., Results: Unique miRNA signatures characterized each subset (mammary stem cell (MaSC)/basal, luminal progenitor, mature luminal, stromal), with a high degree of conservation across species. Comparison of miRNA and transcriptome profiles for the epithelial subtypes revealed an inverse relationship and pinpointed key developmental genes. Interestingly, expression of the primate-specific miRNA cluster (19q13.4) was found to be restricted to the MaSC/basal subset. Comparative analysis of miRNA signatures with H3 lysine modification maps of the different epithelial subsets revealed a tight correlation between active or repressive marks for the top DE miRNAs, including derepression of miRNAs in Ezh2-deficient cellular subsets. Interrogation of TCGA-identified miRNA profiles with the miRNA signatures of different human subsets revealed specific relationships., Conclusions: The derivation of global miRNA expression profiles for the different mammary subpopulations provides a comprehensive resource for understanding the interplay between miRNA networks and target gene expression. These data have highlighted lineage-specific miRNAs and potential miRNA-mRNA networks, some of which are disrupted in neoplasia. Furthermore, our findings suggest that key developmental miRNAs are regulated by global changes in histone modification, thus linking the mammary epigenome with genome-wide changes in the expression of genes and miRNAs. Comparative miRNA signature analyses between normal breast epithelial cells and breast tumors confirmed an important linkage between luminal progenitor cells and basal-like tumors.

Large genomic rearrangements (LGRs) account for at least 10% of the mutations in BRCA1 and 5% of BRCA2 mutations in outbred hereditary breast and ovarian cancer (HBOC) families. Data from some series suggest LGRs represent particularly penetrant mutations. 1,034 index cases from HBOC families underwent comprehensive BRCA1 and BRCA2 mutation testing, including screening for LGRs. The personal and family history of 254 identified mutation carriers were compared based on mutation type. Thirty-six LGRs were detected; 32/122 (26%) BRCA1 and 4/132 (3%) BRCA2 mutations. High risk features (bilateral breast cancer, diagnosis <40 years, ovarian cancer, male breast cancer) were more commonly associated with an LGR than a non-LGR mutation (p = 0.008), In families with a BRCA1 LGR the mean age of breast cancer diagnosis was younger than in families with a non-LGR BRCA1 mutation (42.5 vs. 46.1 years, p = 0.007). Across the entire group of mutation positive families the number of relatives affected by breast or ovarian cancer was increased [LGR 3.7 vs. non- LGR 2.8 per family, p value (adjusted for genotype) = 0.047]. Excluding index cases, the odds ratio for breast cancer in BRCA1 families with an LGR was 1.42 (95% CI 1.24-1.63) and for ovarian cancer 1.66 (95% CI 1.10-2.49). The increased cancer risk was reflected in significantly higher risk assessments by mutation prediction tools. LGRs are associated with higher cancer risks. If validated, LGRs could be included in cancer risk prediction tools to improve personalised cancer risk prediction estimates and may guide cost-minimising mutation screening strategies in some healthcare settings.

Background: The molecular regulators that orchestrate stem cell renewal, proliferation and differentiation along the mammary epithelial hierarchy remain poorly understood. Here we have performed a large-scale pooled RNAi screen in primary mouse mammary stem cell (MaSC)-enriched basal cells using 1295 shRNAs against genes principally involved in transcriptional regulation., Methods: MaSC-enriched basal cells transduced with lentivirus pools carrying shRNAs were maintained as non-adherent mammospheres, a system known to support stem and progenitor cells. Integrated shRNAs that altered culture kinetics were identified by next generation sequencing as relative frequency changes over time. RNA-seq-based expression profiling coupled with in vitro progenitor and in vivo transplantation assays was used to confirm a role for candidate genes in mammary stem and/or progenitor cells., Results: Utilizing a mammosphere-based assay, the screen identified several candidate regulators. Although some genes had been previously implicated in mammary gland development, the vast majority of genes uncovered have no known function within the mammary gland. RNA-seq analysis of freshly purified primary mammary epithelial populations and short-term cultured mammospheres was used to confirm the expression of candidate regulators. Two genes, Asap1 and Prox1, respectively implicated in breast cancer metastasis and progenitor cell function in other systems, were selected for further analysis as their roles in the normal mammary gland were unknown. Both Prox1 and Asap1 were shown to act as negative regulators of progenitor activity in vitro, and Asap1 knock-down led to a marked increase in repopulating activity in vivo, implying a role in stem cell activity., Conclusions: This study has revealed a number of novel genes that influence the activity or survival of mammary stem and/or progenitor cells. Amongst these, we demonstrate that Prox1 and Asap1 behave as negative regulators of mammary stem/progenitor function. Both of these genes have also been implicated in oncogenesis. Our findings provide proof of principle for the use of short-term cultured primary MaSC/basal cells in functional RNAi screens.

Expansion and remodelling of the mammary epithelium requires a tight balance between cellular proliferation, differentiation and death. To explore cell survival versus cell death decisions in this organ, we deleted the pro-survival gene Mcl-1 in the mammary epithelium. Mcl-1 was found to be essential at multiple developmental stages including morphogenesis in puberty and alveologenesis in pregnancy. Moreover, Mcl-1-deficient basal cells were virtually devoid of repopulating activity, suggesting that this gene is required for stem cell function. Profound upregulation of the Mcl-1 protein was evident in alveolar cells at the switch to lactation, and Mcl-1 deficiency impaired lactation. Interestingly, EGF was identified as one of the most highly upregulated genes on lactogenesis and inhibition of EGF or mTOR signalling markedly impaired lactation, with concomitant decreases in Mcl-1 and phosphorylated ribosomal protein S6. These data demonstrate that Mcl-1 is essential for mammopoiesis and identify EGF as a critical trigger of Mcl-1 translation to ensure survival of milk-producing alveolar cells.

Despite advances in the treatment of patients with early and metastatic breast cancer, mortality remains high due to intrinsic or acquired resistance to therapy. Increased understanding of the genomic landscape through massively parallel sequencing has revealed somatic mutations common to specific subtypes of breast cancer, provided new prognostic and predictive markers, and highlighted potential therapeutic targets. Evaluating new targets using established cell lines is limited by the inexact correlation between responsiveness observed in cell lines versus that elicited in the patient. Patient-derived xenografts (PDXs) generated from fresh tumor specimens recapitulate the diversity of breast cancer and reflect histopathology, tumor behavior, and the metastatic properties of the original tumor. The high degree of genomic preservation evident across primary tumors and their matching PDXs over serial passaging validate them as important preclinical tools. Indeed, there is accumulating evidence that PDXs can recapitulate treatment responses of the parental tumor. The finding that tumor engraftment is an independent and poor prognostic indicator of patient outcome represents the first step towards personalized medicine. Here we review the utility of breast cancer PDX models to study the clonal evolution of tumors and to evaluate novel therapies and drug resistance.

Background: Men with germline breast cancer 1, early onset (BRCA1) or breast cancer 2, early onset (BRCA2) gene mutations have a higher risk of developing prostate cancer (PCa) than noncarriers. IMPACT (Identification of Men with a genetic predisposition to ProstAte Cancer: Targeted screening in BRCA1/2 mutation carriers and controls) is an international consortium of 62 centres in 20 countries evaluating the use of targeted PCa screening in men with BRCA1/2 mutations., Objective: To report the first year's screening results for all men at enrollment in the study., Design, Setting and Participants: We recruited men aged 40-69 yr with germline BRCA1/2 mutations and a control group of men who have tested negative for a pathogenic BRCA1 or BRCA2 mutation known to be present in their families. All men underwent prostate-specific antigen (PSA) testing at enrollment, and those men with PSA >3 ng/ml were offered prostate biopsy., Outcome Measurements and Statistical Analysis: PSA levels, PCa incidence, and tumour characteristics were evaluated. The Fisher exact test was used to compare the number of PCa cases among groups and the differences among disease types., Results and Limitations: We recruited 2481 men (791 BRCA1 carriers, 531 BRCA1 controls; 731 BRCA2 carriers, 428 BRCA2 controls). A total of 199 men (8%) presented with PSA >3.0 ng/ml, 162 biopsies were performed, and 59 PCas were diagnosed (18 BRCA1 carriers, 10 BRCA1 controls; 24 BRCA2 carriers, 7 BRCA2 controls); 66% of the tumours were classified as intermediate- or high-risk disease. The positive predictive value (PPV) for biopsy using a PSA threshold of 3.0 ng/ml in BRCA2 mutation carriers was 48%-double the PPV reported in population screening studies. A significant difference in detecting intermediate- or high-risk disease was observed in BRCA2 carriers. Ninety-five percent of the men were white, thus the results cannot be generalised to all ethnic groups., Conclusions: The IMPACT screening network will be useful for targeted PCa screening studies in men with germline genetic risk variants as they are discovered. These preliminary results support the use of targeted PSA screening based on BRCA genotype and show that this screening yields a high proportion of aggressive disease., Patient Summary: In this report, we demonstrate that germline genetic markers can be used to identify men at higher risk of prostate cancer. Targeting screening at these men resulted in the identification of tumours that were more likely to require treatment., (Copyright © 2014 European Association of Urology. All rights reserved.)

Background: Germline loss-of-function mutations in PALB2 are known to confer a predisposition to breast cancer. However, the lifetime risk of breast cancer that is conferred by such mutations remains unknown., Methods: We analyzed the risk of breast cancer among 362 members of 154 families who had deleterious truncating, splice, or deletion mutations in PALB2. The age-specific breast-cancer risk for mutation carriers was estimated with the use of a modified segregation-analysis approach that allowed for the effects of PALB2 genotype and residual familial aggregation., Results: The risk of breast cancer for female PALB2 mutation carriers, as compared with the general population, was eight to nine times as high among those younger than 40 years of age, six to eight times as high among those 40 to 60 years of age, and five times as high among those older than 60 years of age. The estimated cumulative risk of breast cancer among female mutation carriers was 14% (95% confidence interval [CI], 9 to 20) by 50 years of age and 35% (95% CI, 26 to 46) by 70 years of age. Breast-cancer risk was also significantly influenced by birth cohort (P<0.001) and by other familial factors (P=0.04). The absolute breast-cancer risk for PALB2 female mutation carriers by 70 years of age ranged from 33% (95% CI, 25 to 44) for those with no family history of breast cancer to 58% (95% CI, 50 to 66) for those with two or more first-degree relatives with breast cancer at 50 years of age., Conclusions: Loss-of-function mutations in PALB2 are an important cause of hereditary breast cancer, with respect both to the frequency of cancer-predisposing mutations and to the risk associated with them. Our data suggest the breast-cancer risk for PALB2 mutation carriers may overlap with that for BRCA2 mutation carriers. (Funded by the European Research Council and others.).

The HLH transcriptional regulator Id4 exerts important roles in different organs, including the neural compartment, where Id4 loss usually results in early lethality. To explore the role of this basally restricted transcription factor in the mammary gland, we generated a cre-inducible mouse model. MMTV- or K14-cre-mediated deletion of Id4 led to a delay in ductal morphogenesis, consistent with previous findings using a germ-line knockout mouse model. A striking increase in the expression of ERα (Esr1), PR and FoxA1 was observed in both the basal and luminal cellular subsets of Id4-deficient mammary glands. Together with chromatin immunoprecipitation of Id4 on the Esr1 and Foxa1 promoter regions, these data imply that Id4 is a negative regulator of the ERα signaling axis. Unexpectedly, examination of the ovaries of targeted mice revealed significantly increased numbers of secondary and antral follicles, and reduced Id4 expression in the granulosa cells. Moreover, expression of the cascade of enzymes that are crucial for estrogen biosynthesis in the ovary was decreased in Id4-deficient females and uterine weights were considerably lower, indicating impaired estrogen production. Thus, compromised ovarian function and decreased circulating estrogen likely contribute to the mammary ductal defects evident in Id4-deficient mice. Collectively, these data identify Id4 as a novel regulator of estrogen signaling, where Id4 restrains ERα expression in the basal and luminal cellular compartments of the mammary gland and regulates estrogen biosynthesis in the ovary., (© 2014. Published by The Company of Biologists Ltd.)

The mammary epithelium undergoes profound morphogenetic changes during development. Architecturally, it comprises two primary lineages, the inner luminal and outer myoepithelial cell layers. Two opposing concepts on the nature of mammary stem cells (MaSCs) in the postnatal gland have emerged. One model, based on classical transplantation assays, postulates that bipotent MaSCs have a key role in coordinating ductal epithelial expansion and maintenance in the adult gland, whereas the second model proposes that only unipotent MaSCs identified by lineage tracing contribute to these processes. Through clonal cell-fate mapping studies using a stochastic multicolour cre reporter combined with a new three-dimensional imaging strategy, we provide evidence for the existence of bipotent MaSCs as well as distinct long-lived progenitor cells. The cellular dynamics at different developmental stages support a model in which both stem and progenitor cells drive morphogenesis during puberty, whereas bipotent MaSCs coordinate ductal homeostasis and remodelling of the mouse adult gland.

The mammary epithelium undergoes enormous morphogenetic changes during the lifespan of a mammal. The recent elucidation of an epithelial differentiation hierarchy in the mouse mammary gland through classical transplantation and clonogenic assays has pointed to the existence of multipotent mammary stem cells (MaSCs) and at least two distinct luminal progenitor types. Moreover, an analogous functional hierarchy has been defined in human breast tissue. The existence of slow cycling stem cells, both long- and short-term repopulating cells, and a unique fetal MaSC population, imply a complex stem cell compartment within the mammary gland. The recent discovery of unipotent stem-like cells from lineage tracing studies has added a further layer of complexity to the emerging differentiation hierarchy. Although the precise relationships between stem and progenitor cells have yet to be resolved, the epithelial hierarchy has provided an important framework for elucidating the roles of molecular regulators of mammary gland ontogeny and understanding potential cells of origin in breast cancer., (© 2014 Elsevier Inc. All rights reserved.)

The familial aggregation of breast cancer has been well-described with approximately 25% of breast cancers attributable to inherited mutations in currently known breast cancer susceptibility genes. PALB2 c.3113G>A (p.Trp1038*) is a protein-truncating mutation which has been associated with high estimated risk of breast cancer in Australian women (91%; 95% CI = 44-100) to age 70 years. This study screened for PALB2 c.3113G>A in germline DNA representing 871 unrelated individuals from "high-risk" breast and/or ovarian cancer families evaluated in the setting of a Familial Cancer Centre in Australia. The PALB2 c.3113G>A mutation was identified in eight of 871 probands (0.92%) from these families. Median age of diagnosis was 42 years. Five of these eight women had contra-lateral breast cancers. Available data suggests that PALB2 c.3113G>A is a rare mutation with estimated breast cancer risks similar in magnitude to that associated with BRCA2 mutations. Although the proportion of high-risk women carrying this PALB2 mutation is low, research efforts should continue in order to effect its translation into clinical genetic testing practice.

The interaction between breast tumor epithelial and stromal cells is vital for initial and recurrent tumor growth. While breast cancer-associated stromal cells provide a favorable environment for proliferation and metastasis, the molecular mechanisms contributing to this process are not fully understood. Nuclear receptors (NRs) are intracellular transcription factors that directly regulate gene expression. Little is known about the status of NRs in cancer-associated stroma. Nuclear Receptor Low-Density Taqman Arrays were used to compare the gene expression profiles of all 48 NR family members in a collection of primary cultured cancer-associated fibroblasts (CAFs) obtained from estrogen receptor (ER)α positive breast cancers (n = 9) and normal breast adipose fibroblasts (NAFs) (n = 7). Thirty-three of 48 NRs were expressed in both the groups, while 11 NRs were not detected in either. Three NRs (dosage-sensitive sex reversal, adrenal hypoplasia critical region, on chromosome X, gene 1 (DAX-1); estrogen-related receptor beta (ERR-β); and RAR-related orphan receptor beta (ROR-β)) were only detected in NAFs, while one NR (liver receptor homolog-1 (LRH-1)) was unique to CAFs. Of the NRs co-expressed, four were significantly down-regulated in CAFs compared with NAFs (RAR-related orphan receptor-α (ROR-α); Thyroid hormone receptor-β (TR-β); vitamin D receptor (VDR); and peroxisome proliferator-activated receptor-γ (PPAR-γ)). Quantitative immunohistochemistry for LRH-1, TR-β, and PPAR-γ proteins in stromal fibroblasts from an independent panel of breast cancers (ER-positive (n = 15), ER-negative (n = 15), normal (n = 14)) positively correlated with mRNA expression profiles. The differentially expressed NRs identified in tumor stroma are key mediators in aromatase regulation and subsequent estrogen production. Our findings reveal a distinct pattern of NR expression that therefore fits with a sustained and increased local estrogen microenvironment in ER-positive tumors. NRs in CAFs may provide a new avenue for the development of intratumoral-targeted therapies in breast cancer.

Background: Population-based studies of breast cancer have estimated that at least some PALB2 mutations are associated with high breast cancer risk. For women carrying PALB2 mutations, knowing their carrier status could be useful in directing them towards effective cancer risk management and therapeutic strategies. We sought to determine whether morphological features of breast tumours can predict PALB2 germline mutation status., Methods: Systematic pathology review was conducted on breast tumours from 28 female carriers of PALB2 mutations (non-carriers of other known high-risk mutations, recruited through various resources with varying ascertainment) and on breast tumours from a population-based sample of 828 Australian women diagnosed before the age of 60 years (which included 40 BRCA1 and 18 BRCA2 mutation carriers). Tumour morphological features of the 28 PALB2 mutation carriers were compared with those of 770 women without high-risk mutations., Results: Tumours arising in PALB2 mutation carriers were associated with minimal sclerosis (odds ratio (OR)=19.7; 95% confidence interval (CI)=6.0-64.6; P=5 × 10(-7)). Minimal sclerosis was also a feature that distinguished PALB2 mutation carriers from BRCA1 (P=0.05) and BRCA2 (P=0.04) mutation carriers., Conclusion: This study identified minimal sclerosis to be a predictor of germline PALB2 mutation status. Morphological review can therefore facilitate the identification of women most likely to carry mutations in PALB2.

The prosurvival protein BCL-2 is frequently overexpressed in estrogen receptor (ER)-positive breast cancer. We have generated ER-positive primary breast tumor xenografts that recapitulate the primary tumors and demonstrate that the BH3 mimetic ABT-737 markedly improves tumor response to the antiestrogen tamoxifen. Despite abundant BCL-XL expression, similar efficacy was observed with the BCL-2 selective inhibitor ABT-199, revealing that BCL-2 is a crucial target. Unexpectedly, BH3 mimetics were found to counteract the side effect of tamoxifen-induced endometrial hyperplasia. Moreover, BH3 mimetics synergized with phosphatidylinositol 3-kinase (PI3K)/mammalian target of rapamycin (mTOR) inhibitors in eliciting apoptosis. Importantly, these two classes of inhibitor further enhanced tumor response in combination therapy with tamoxifen. Collectively, our findings provide a rationale for the clinical evaluation of BH3 mimetics in therapy for breast cancer., (Copyright © 2013 Elsevier Inc. All rights reserved.)

The mammary epithelium is a dynamic, highly hormone-responsive tissue. To explore chromatin modifications underlying its lineage specification and hormone responsiveness, we determined genome-wide histone methylation profiles of mammary epithelial subpopulations in different states. The marked differences in H3K27 trimethylation between subpopulations in the adult gland suggest that epithelial cell-fate decisions are orchestrated by polycomb-complex-mediated repression. Remarkably, the mammary epigenome underwent highly specific changes in different hormonal contexts, with a profound change being observed in the global H3K27me3 map of luminal cells during pregnancy. We therefore examined the role of the key H3K27 methyltransferase Ezh2 in mammary physiology. Its expression and phosphorylation coincided with H3K27me3 modifications and peaked during pregnancy, driven in part by progesterone. Targeted deletion of Ezh2 impaired alveologenesis during pregnancy, preventing lactation, and drastically reduced stem/progenitor cell numbers. Taken together, these findings reveal that Ezh2 couples hormonal stimuli to epigenetic changes that underpin progenitor activity, lineage specificity, and alveolar expansion in the mammary gland., (Copyright © 2013 The Authors. Published by Elsevier Inc. All rights reserved.)