Is BRCA1/BRCA2-related breast carcinogenesis estrogen dependent?

ER-positive and BRCA2-mutated breast cancer: a literature review

BRCA2-mutated carriers have a high lifetime risk of breast cancer (BC), an early age of onset, and an increased risk of other cancers (including ovarian, pancreatic, and prostate cancer). Almost 70-80% of BRCA2-mutated BC are estrogen receptor (ER)-positive, which is a particular type of ER-positive BC that differs from sporadic ER-positive BC. This article reviews the clinicopathological features, treatment, and prognosis of ER-positive and BRCA2-mutated BC to provide a reference for clinical decision-making.

Triple-negative breast cancer: epidemiology, molecular mechanisms, and modern vaccine-based treatment strategies

Long-standing scarcity of efficacious treatments and tumor heterogeneity have contributed to triple-negative breast cancer (TNBC), a subtype with a poor prognosis and aggressive behavior that accounts for 10-15% of all new cases of breast cancer. TNBC is characterized by the absence of progesterone and estrogen receptor expression and lacks gene amplification or overexpression of HER2. Genomic sequencing has detected that the unique mutational profile of both the somatic and germline modifications in TNBC is staggeringly dissimilar from other breast tumor subtypes. The clinical utility of sequencing germline BRCA1/2 genes has been well established in TNBC. Nevertheless, reports regarding the penetrance and risk of other susceptibility genes are relatively scarce. Recurring mutations (e.g., TP53 and PI3KCA mutations) occur together with rare mutations in TNBC, and the shared effects of genomic modifications drive its progression. Given the heterogeneity and complexity of this disease, a clinical understanding of the genomic modifications in TNBC can pave an innovative way toward its therapy. In this review, we summarized the most recent discoveries associated with the underlying biology of developmental signaling pathways in TNBC. We also summarize the recent advancements in genetics and epidemiology and discuss state-of-the-art vaccine-based therapeutic strategies for TNBC that will enable tailored therapeutics.

The BRCA2 missense mutation K2497R suppressed self-degradation and increased ATP production and cell proliferation

Breast cancer susceptibility gene 2 (BRCA2) mediates genome maintenance during the S phase of the cell cycle, with important roles in replication stress, centrosome replication, and cytokinesis. In this study, we showed that a small heat shock protein, HSP27, interacted with and participated in the degradation of BRCA2 in estrogen-treated MCF-7 cells. BRCA2 degradation reportedly requires ubiquitination of the C-terminal region; thus, fragments of amino acid (aa) residues 2241-2940 were produced and assayed for their degradation following cycloheximide (CHX) treatment. The results showed that aa 2491-2580 affected the degradation of BRCA2, especially lysine (Lys) 2497. Furthermore, the K2497 A/R mutation increased ATP production and the proliferation of DLD-1 (BRCA2 knockout) cells compared to the cells expressing wild-type BRCA2-FLAG. Notably, a single residue, Lys2497, affected BRCA2 degradation, and K2497R is reportedly a missense mutation in hereditary breast cancer.

Functional Evaluation of ZNF350 Missense Genetic Variants Associated with Breast Cancer Susceptibility

ZNF350, a BRCA1-interacting protein, could mediate BRCA1-induced sequence-specific transcriptional repression of several genes, including GADD45α. As a potential breast cancer susceptibility gene, single nucleotide polymorphisms (SNPs), especially missense SNPs, may influence the transcriptional repression of its target tumor suppressor genes and individuals' breast cancer risk. Using the gene-based haplotype-tagging SNPs strategy, we evaluated the association between six ZNF350 polymorphisms and breast cancer risk in a case-control set from a northern Chinese population. The impact of ZNF350 variations on transcriptional repression of GADD45α was also examined. It was found that ZNF350 rs2278420 (L66P) and rs2278415 (S501R) missense genetic variants are in complete linkage disequilibrium and have a significant impact on inter-individual susceptibility to breast cancer. Additionally, ZNF350 GGCGT or GGCGC haplotype is also associated with a significantly increased breast cancer risk compared with the GGCAC haplotype. ZNF350 L66P variant modifies the risk of breast cancer not only by itself but also in a gene-environment interaction manner with age, age at menarche, menopause status, or estrogen receptor status. Interestingly, we observed that ZNF350 L66P and S501R SNPs could weaken the capability of ZNF350-mediated GADD45α transcription repression and it may be an underlying mechanism of the observed epidemiological associations. Our results highlight ZNF350 as an important gene in human mammary oncogenesis and ZNF350 missense genetic polymorphisms confer susceptibility to breast cancer.

Proliferation and ovarian hormone signaling are impaired in normal breast tissues from women with BRCA1 mutations: benefit of a progesterone receptor modulator treatment as a breast cancer preventive strategy in women with inherited BRCA1 mutations

Women with inherited BRCA1 mutations have an elevated risk (40-80%) for developing breast and ovarian cancers. Reproductive history has been reported to alter this risk, suggesting a relationship between ovarian hormone signaling and BRCA1-related tumor development. BRCA1 interactions with estrogen receptor (ER) and progesterone receptor (PR) signaling were previously described in human breast cancer cell lines and mouse models. However, few studies have examined the effect of ovarian hormone regulation in normal human breast tissues bearing a heterozygous BRCA1 mutation. This study compares the proliferation level (Ki67) and the expression of ER, PR, and of the PR target gene, fatty acid synthase (FASN), in histologically normal breast tissues from women with BRCA1 mutations (BRCA1+/mut, n=23) or without BRCA1 mutations (BRCA1+/+, n=28). BRCA1+/mut tissues showed an increased proliferation and impaired hormone receptor expression with a marked loss of the PR isoform, PR-B. Responses to estradiol and progesterone treatments in BRCA1+/mut and BRCA1+/+ breast tissues were studied in a mouse xenograft model, and showed that PR and FASN expression were deregulated in BRCA1+/mut breast tissues. Progesterone added to estradiol treatment increased the proliferation in a subset of BRCA1+/mut breast tissues. The PR inhibitor, ulipristal acetate (UPA), was able to reverse this aberrant progesterone-induced proliferation. This study suggests that a subset of women with BRCA1 mutations could be candidates for a UPA treatment as a preventive breast cancer strategy.

[Hormonotherapy for breast cancer prevention: What about women with genetic predisposition to breast cancer?]

In France, women carrying BRCA1/2 mutation, at an identified high risk of breast cancer are recommended to undergo breast MRI screening. That screening does not however prevent the risk of developing a breast cancer. The only alternative to breast cancer screening available in France is surgical prevention by prophylactic mastectomy. An interesting option for women who wish to reduce their breast cancer risk, but are unready for prophylactic mastectomy is a preventive hormonal treatment by aromatase inhibitors, or selective estrogens receptor modulators (SERMs). Reliable clinical trials show the efficiency of tamoxifen, raloxifen, exemestane, and anastrozole especially, in reducing breast cancer incidence by 33%, 34%, 65% and 53% respectively. This article tries to sum up the main published trials of breast cancer prevention with hormonal treatment, and presents the latest American and English clinical guidelines concerning hormonal prevention for women at high risk of breast cancer, and starts thinking about the possibilities of hormonoprevention, especially among women carrying a BRCA1/2 mutation in France.

The role of body size and physical activity on the risk of breast cancer in BRCA mutation carriers

Women who inherit a BRCA mutation face a high lifetime risk of developing breast cancer. Given the high penetrance of these mutations, prevention is of extreme importance. Here, we review the literature regarding the role of body size and of physical activity in the context of BRCA-associated breast cancer. There is some evidence to support a protective role of a healthy body size and of regular physical activity among mutation carriers, particularly during adolescence or early adulthood. Factors which increase the physiologic expression of the normal copy of the BRCA1 or BRCA2 gene and thereby normalize protein levels, contribute to stem cell homeostasis, and/or affect hormone levels, might mitigate the effects of an inherited BRCA mutation. Preliminary evidence from one in vivo study and from one epidemiologic report suggests that an increase in BRCA1 mRNA expression occurs with increasing levels of physical activity. The prospect of changing lifestyle for the purpose of preventing breast cancer in high-risk women, complemented by mechanistic evidence, warrants evaluation in large-scale prospective studies.

[Breast and ovarian cancer due to BRCA1&2 hereditary cancer predisposition syndrome and reproduction: literature review]

INTRODUCTION

Germline mutations BRCA1&2 are responsible in women for breast and ovarian cancers that commonly occur at a young age: as such, there are strong interactions between the oncological risks and the events of reproductive life, pregnancy, breastfeeding, and management of infertility.

MATERIALS AND METHODS

A review of the international literature from the PubMed database was conducted, and recommendations of French health agencies were exposed. Published studies are case-control and cohort studies in the majority, with a low level of evidence.

RESULTS

Pregnancy and lactation have no effect on breast and ovaries or even decreases the risk. The sex ratio among patients carrying the mutation is in favor of girls. It is not observed more infertility in patients carrying a mutation despite a strong suspicion of premature ovarian failure, and infertility treatments do not increase breast and ovarian risk. There are ethical debates concerning the place of pre-natal diagnosis: both experts and concerned patients recommend a case-by-case analysis of the requests.

Integrity of the LXXLL motif in Stat6 is required for the inhibition of breast cancer cell growth and enhancement of differentiation in the context of progesterone

Background

Progesterone is essential for the proliferation and differentiation of mammary gland epithelium. Studies of breast cancer cells have demonstrated a biphasic progesterone response consisting of an initial proliferative burst followed by sustained growth arrest. However, the transcriptional factors acting with the progesterone receptor (PR) to mediate the effects of progesterone on mammary cell growth and differentiation remain to be determined. Recently, it was demonstrated that signal transducer and activator of transcription 6 (Stat6) is a cell growth suppressor. Similar to progesterone-bound PR, Stat6 acts by inducing the expression of the G1 cyclin-dependent kinase inhibitors p21 and p27. The possible interaction between Stat6 and progesterone pathways in mammary cells was therefore investigated in the present study.

Methods

ChIP and luciferase were assayed to determine whether Stat6 induces p21 and p27 expression by recruitment at the proximal Sp1-binding sites of the gene promoters. Immunoprecipitation and Western blotting were performed to investigate the interaction between Stat6 and PR-B. The cellular DNA content and cell cycle distribution in breast cancer cells were analyzed by FACS.

Results

We found that Stat6 interacts with progesterone-activated PR in T47D cells. Stat6 synergizes with progesterone-bound PR to transactivate the p21 and p27 gene promoters at the proximal Sp1-binding sites. Moreover, Stat6 overexpression and knockdown, respectively, increased or prevented the induction of p21 and p27 gene expression by progesterone. Stat6 knockdown also abolished the inhibitory effects of progesterone on pRB phosphorylation, G1/S cell cycle progression, and cell proliferation. In addition, knockdown of Stat6 expression prevented the induction of breast cell differentiation markers, previously identified as progesterone target genes. Finally, Stat6 gene expression levels increased following progesterone treatment, indicating a positive auto-regulatory loop between PR and Stat6.

Conclusions

Taken together, these data identify Stat6 as a coactivator of PR mediating the growth-inhibitory and differentiation effects of progesterone on breast cancer cells.

Tamoxifen and risk of contralateral breast cancer for BRCA1 and BRCA2 mutation carriers

PURPOSE

To determine whether adjuvant tamoxifen treatment for breast cancer (BC) is associated with reduced contralateral breast cancer (CBC) risk for BRCA1 and/or BRCA2 mutation carriers.

METHODS

Analysis of pooled observational cohort data, self-reported at enrollment and at follow-up from the International BRCA1, and BRCA2 Carrier Cohort Study, Kathleen Cuningham Foundation Consortium for Research into Familial Breast Cancer, and Breast Cancer Family Registry. Eligible women were BRCA1 and BRCA2 mutation carriers diagnosed with unilateral BC since 1970 and no other invasive cancer or tamoxifen use before first BC. Hazard ratios (HRs) for CBC associated with tamoxifen use were estimated using Cox regression, adjusting for year and age of diagnosis, country, and bilateral oophorectomy and censoring at contralateral mastectomy, death, or loss to follow-up.

RESULTS

Of 1,583 BRCA1 and 881 BRCA2 mutation carriers, 383 (24%) and 454 (52%), respectively, took tamoxifen after first BC diagnosis. There were 520 CBCs over 20,104 person-years of observation. The adjusted HR estimates were 0.38 (95% CI, 0.27 to 0.55) and 0.33 (95% CI, 0.22 to 0.50) for BRCA1 and BRCA2 mutation carriers, respectively. After left truncating at recruitment to the cohort, adjusted HR estimates were 0.58 (95% CI, 0.29 to 1.13) and 0.48 (95% CI, 0.22 to 1.05) based on 657 BRCA1 and 426 BRCA2 mutation carriers with 100 CBCs over 4,392 person-years of prospective follow-up. HRs did not differ by estrogen receptor status of the first BC (missing for 56% of cases).

CONCLUSION

This study provides evidence that tamoxifen use is associated with a reduction in CBC risk for BRCA1 and BRCA2 mutation carriers. Further follow-up of these cohorts will provide increased statistical power for future prospective analyses.

Uptake of a randomized breast cancer prevention trial comparing letrozole to placebo in BRCA1/2 mutations carriers: the LIBER trial

Women with germline BRCA1 or BRCA2 (BRCA1/2) mutations are considered as an extreme risk population for developing breast cancer. Prophylactic mastectomy provides a valid option to reduce such risk, impacting however, the quality of life. Medical prevention by aromatase inhibitor that has also recently shown to have preventive effect may thus be considered as an alternative. LIBER is an ongoing double-blind, randomized phase III trial to evaluate the efficacy of 5-year letrozole versus placebo to decrease breast cancer incidence in post-menopausal BRCA1/2 mutation carriers (NCT00673335). We present data on the uptake of this trial. We compared characteristics of women in the LIBER trial (n = 113) to those of women enrolled in the prospective ongoing national GENEPSO cohort (n = 1,505). Uptake was evaluated through a survey sent to all active centres, with responses obtained from 17 to the 20 (85%) centres. According to the characteristics of the women enrolled in the GENEPSO cohort and the survey, approximately one-third of BRCA1/2 mutation carriers were eligible for the trial. Five hundred and thirty-four women eligible from chart review have been informed by mail about the prevention trial and were invited to an oral information by participating centres. Forty-four percentage of them came to the dedicated medical visit. Uptake of drug prevention trial was 32% among women informed orally and 15% of all the eligible women. The main reasons of refusal were: potential side effects, probability to receive the placebo and lack of support from their physicians. Additionally, we noticed that prior prophylactic oophorectomy and previous unilateral breast cancer were more frequent in women enrolled in the LIBER trial than in the French cohort (93% vs. 60% and 50% vs. 39%, respectively). Based on an overall 15% uptake among all eligible subjects, greater and wider information of the trial should be offered to women with BRCA1/2 mutation to improve recruitment. Women with previous unilateral breast cancer or prior prophylactic oophorectomy are more likely to enter a medical prevention trial.

Gynaecologic challenging issues in the management of BRCA mutation carriers: oral contraceptives, prophylactic salpingo-oophorectomy and hormone replacement therapy

BRCA1 and BRCA2 mutation carriers have a 54-85% and 45% lifetime risk of developing breast cancer, respectively, and a 18-60% and 11-27% lifetime risk of developing ovarian cancer, respectively. Oral contraceptives (OCs) significantly reduce the risk of ovarian cancer also in BRCA1/BRCA2 mutation carriers. The association between OC use and breast cancer risk in these women is controversial. Some studies showed a modestly increased risk especially among BRCA1 mutation carriers. The risk appears to be greater for women who took OCs for at least 5 years and who took OCs before the age of 30 years. Other studies reported that duration of use before first full-term pregnancy has a positive association with breast cancer risk. Salpingo-oophorectomy reduces the risk of coelomic epithelial cancer of 80-95% and the risk of breast cancer of approximately 50%. BRCA1 and BRCA2 mutation carriers should be encouraged to undergo prophylactic bilateral salpingo-oophorectomy at the age of 35-40 years or when childbearing is complete. Short-term use of hormone replacement therapy may relieve menopausal symptoms and does not appear to affect the breast cancer risk reduction obtained with salpingo-oophorectomy.

Proteomic analysis of breast tissue and nipple aspirate fluid for breast cancer detection

Clinical proteomics has great promise, but many hurdles. Proteomic approaches may prove to be the answer to decades of frustrating searches for markers that are specific and selective for breast cancer. In order to achieve this goal, the challenge arises that breast cancer is a heterogeneous disease and individual variations are enormous. To identify sensitive and specific breast cancer markers will require standardization of every method, from tissue collection through statistical analysis and diligence. Small pilot studies of tumors with varied characteristics will not suffice; large, homogeneous sample sets will be the most efficient route to identify breast cancer markers. Proteomic analysis of nipple aspirate fluid may identify markers that can be used for screening with this noninvasive technique. Proteomic analysis of breast biopsies will allow more detailed characterization of the individual's cancer, with therapy tailored to the disease based on this information.

ERalpha-negative and triple negative breast cancer: molecular features and potential therapeutic approaches

Triple negative breast cancer (TNBC) is a type of aggressive breast cancer lacking the expression of estrogen receptors (ER), progesterone receptors (PR) and human epidermal growth factor receptor-2 (HER-2). TNBC patients account for approximately 15% of total breast cancer patients and are more prevalent among young African, African-American and Latino women patients. The currently available ER-targeted and Her-2-based therapies are not effective for treating TNBC. Recent studies have revealed a number of novel features of TNBC. In the present work, we comprehensively addressed these features and discussed potential therapeutic approaches based on these features for TNBC, with particular focus on: 1) the pathological features of TNBC/basal-like breast cancer; 2) E(2)/ERbeta-mediated signaling pathways; 3) G-protein coupling receptor-30/epithelial growth factor receptor (GPCR-30/EGFR) signaling pathway; 4) interactions of ERbeta with breast cancer 1/2 (BRCA1/2); 5) chemokine CXCL8 and related chemokines; 6) altered microRNA signatures and suppression of ERalpha expression/ERalpha-signaling by micro-RNAs; 7) altered expression of several pro-oncongenic and tumor suppressor proteins; and 8) genotoxic effects caused by oxidative estrogen metabolites. Gaining better insights into these molecular pathways in TNBC may lead to identification of novel biomarkers and targets for development of diagnostic and therapeutic approaches for prevention and treatment of TNBC.

Chromatin-remodelling mechanisms in cancer

Chromatin-remodelling mechanisms include DNA methylation, histone-tail acetylation, poly-ADP-ribosylation, and ATP-dependent chromatin-remodelling processes. Some epigenetic modifications among others have been observed in cancer cells, namely (1) local DNA hypermethylation and global hypomethylation, (2) alteration in histone acetylation/deacetylation balance, (3) increased or decreased poly-ADP-ribosylation, and (4) failures in ATP-dependent chromatin-remodelling mechanisms. Moreover, these alterations can influence the response to classical anti-tumour treatments. Drugs targeting epigenetic alterations are under development. Currently, DNA methylation and histone deacetylase inhibitors are in use in cancer therapy, and poly-ADP-ribosylation inhibitors are undergoing clinical trials. Epigenetic therapy is gaining in importance in pharmacology as a new tool to improve anti-cancer therapies.

Induction of A.T to G.C mutations by erroneous repair of depurinated DNA following estrogen treatment of the mammary gland of ACI rats

Evidence suggests that the genotoxic mechanism of estrogens (estrone/estradiol) in breast cancer involves their oxidation to 3,4-quinones and reaction with DNA to form depurinating N3Ade and N7Gua adducts. We examined whether estrogen genotoxicity is mutagenic in the mammary gland of the female ACI rat, a model for estrogen-dependent breast cancer. Mutagenesis was studied by PCR amplification of the H-ras1 gene (exons 1-2), cloning in pUC18, transforming Escherichia coli, and sequencing the inserts in plasmids from individual colonies. Mammary glands of both estrogen-responsive (ACI and DA) and resistant (Sprague-Dawley) rats contained pre-existing mutations at frequencies of (39.8-58.8)x10(-5), the majority (62.5-100%) of which were A.T to G.C transitions. Estradiol-3,4-quinone (200 nmol) treatment of ACI rats caused rapid (6h to 1 day) mutagenesis (frequency (83.3-156.1)x10(-5); A.T to G.C 70-73.3%). The estrogen-induced A.T to G.C mutations were detected as G.T heteroduplexes, as would be expected if N3Ade depurinations caused Gua misincorporations by erroneous repair. These heteroduplexes were identified by the T.G-DNA glycosylase (TDG) assay. TDG converts G.T heteroduplexes to G.abasic sites, rendering DNA templates refractory to PCR amplification. Consequently, A.T to G.C mutations present as G.T heteroduplexes in the DNA are eliminated from the spectra. TDG treatment of mammary DNA from estradiol-3,4-quinone-treated ACI rats brought A.T to G.C mutations down to pre-existing frequencies. Our results demonstrate that treatment with estradiol-3,4-quinone, an important metabolite of estrogens, produced A.T to G.C mutations in the DNA of the mammary gland of ACI rats.

Mouse models of BRCA1 and BRCA2 deficiency: past lessons, current understanding and future prospects

Germline mutations in BRCA1 and BRCA2 are responsible for a large proportion of hereditary breast and ovarian cancers. Soon after the identification of both genes in the mid-1990s, investigators set out to develop mouse models for the associated disease. Whereas conventional Brca1 and Brca2 mouse mutants did not reveal a strong phenotype in a heterozygous setting, most homozygous mutations caused embryonic lethality. Consequently, development of mouse models for BRCA-associated tumorigenesis required the generation of tissue-specific conditional knockout animals. In this review, we give an overview of the conventional and the conditional mouse models of BRCA1 and BRCA2 deficiency generated over the last decade, as well as the contribution of these models to our understanding of the biological and molecular functions of BRCA1 and BRCA2. The most advanced mouse models for BRCA1- and BRCA2-associated tumorigenesis mimic human disease to the extent that they can be used in studies addressing clinically relevant questions. These models will help to resolve yet unanswered questions and to translate our increasing knowledge of BRCA1 and BRCA2 biology into clinical practice.