Molecular basis of pregnancy-induced breast cancer protection

Pregnancy Reduces Il33+ Hybrid Progenitor Accumulation in the Aged Mammary Gland

Aging increases breast cancer risk while an early first pregnancy reduces a woman's life-long risk. Several studies have explored the effect of either aging or pregnancy on mammary epithelial cells (MECs), but the combined effect of both remains unclear. Here, we interrogate the functional and transcriptomic changes at single cell resolution in the mammary gland of aged nulliparous and parous mice to discover that pregnancy normalizes age-related imbalances in lineage composition, while also inducing a differentiated cell state. Importantly, we uncover a minority population of Il33-expressing hybrid MECs with high cellular potency that accumulate in aged nulliparous mice but is significantly reduced in aged parous mice. Functionally, IL33 treatment of basal, but not luminal, epithelial cells from young mice phenocopies aged nulliparous MECs and promotes formation of organoids with Trp53 knockdown. Collectively, our study demonstrates that pregnancy blocks the age-associated loss of lineage integrity in the basal layer through a decrease in Il33+ hybrid MECs, potentially contributing to pregnancy-induced breast cancer protection.

Dual role of pregnancy in breast cancer risk

Reproductive history is one of the strongest risk factors for breast cancer in women. Pregnancy can promote short-term breast cancer risk, but also reduce a woman's lifetime risk of breast cancer. Changes in hormone levels before and after pregnancy are one of the key factors in breast cancer risk. This article summarizes the changes in hormone levels before and after pregnancy, and the roles of hormones in mammary gland development and breast cancer progression. Other factors, such as changes in breast morphology and mammary gland differentiation, changes in the proportion of mammary stem cells (MaSCs), changes in the immune and inflammatory environment, and changes in lactation before and after pregnancy, also play key roles in the occurrence and development of breast cancer. This review discusses the dual effects and the potential mechanisms of pregnancy on breast cancer risk from the above aspects, which is helpful to understand the complexity of female breast cancer occurrence.

New Biomarkers and Treatment Advances in Triple-Negative Breast Cancer

Triple-negative breast cancer (TNBC) is a specific subtype of breast cancer lacking hormone receptor expression and HER2 gene amplification. TNBC represents a heterogeneous subtype of breast cancer, characterized by poor prognosis, high invasiveness, high metastatic potential, and a tendency to relapse. In this review, the specific molecular subtypes and pathological aspects of triple-negative breast cancer are illustrated, with particular attention to the biomarker characteristics of TNBC, namely: regulators of cell proliferation and migration and angiogenesis, apoptosis-regulating proteins, regulators of DNA damage response, immune checkpoints, and epigenetic modifications. This paper also focuses on omics approaches to exploring TNBC, such as genomics to identify cancer-specific mutations, epigenomics to identify altered epigenetic landscapes in cancer cells, and transcriptomics to explore differential mRNA and protein expression. Moreover, updated neoadjuvant treatments for TNBC are also mentioned, underlining the role of immunotherapy and novel and targeted agents in the treatment of TNBC.

Breast Carcinogenesis during Pregnancy: Molecular Mechanisms, Maternal and Fetal Adverse Outcomes

Breast cancer is a common type of cancer diagnosed during pregnancy, with increasing incidence over the last years, as more women choose to delay childbearing. Compared to breast cancer in general population, pregnancy-associated breast cancer (PABC) is significantly different in its terms of epidemiology, diagnostic and therapeutic management, while it exhibits particularly aggressive behavior, deriving from its unique molecular and biological profile. Although not fully elucidated, the pathophysiological basis of PABC can be traced back to a combination of hormonal and immune changes during pregnancy, breast involution and altered gene expression. There is considerable controversy in the existing literature about the influence of PABC on pregnancy outcomes, regarding both short- and long-term effects on maternal and fetal/neonatal health. The majority of PABC patients have advanced-stage disease at initial diagnosis and face a significantly poorer prognosis, with decreased survival rates. The most commonly reported adverse obstetrical–fetal events are preterm delivery and prematurity-associated neonatal morbidity, while other neonatal treatment-associated complications might also occur, even when safe therapeutic options are applied during pregnancy. The objective of the present comprehensive review was to summarize current knowledge and up-to-date evidence about the pathophysiological, molecular and biological basis of PABC, as well as its association with adverse maternal, obstetrical, fetal and neonatal outcomes.

Induced mammary cancer in rat models: pathogenesis, genetics, and relevance to female breast cancer

Mammary cancer, or breast cancer in women, is a polygenic disease with a complex etiopathogenesis. While much remains elusive regarding its origin, it is well established that chemical carcinogens and endogenous estrogens contribute significantly to the initiation and progression of this disease. Rats have been useful models to study induced mammary cancer. They develop mammary tumors with comparable histopathology to humans and exhibit differences in resistance or susceptibility to mammary cancer depending on strain. While some rat strains (e.g., Sprague-Dawley) readily form mammary tumors following treatment with the chemical carcinogen, 7,12-dimethylbenz[a]-anthracene (DMBA), other strains (e.g., Copenhagen) are resistant to DMBA-induced mammary carcinogenesis. Genetic linkage in inbred strains has identified strain-specific quantitative trait loci (QTLs) affecting mammary tumors, via mechanisms that act together to promote or attenuate, and include 24 QTLs controlling the outcome of chemical induction, 10 QTLs controlling the outcome of estrogen induction, and 4 QTLs controlling the outcome of irradiation induction. Moreover, and based on shared factors affecting mammary cancer etiopathogenesis between rats and humans, including orthologous risk regions between both species, rats have served as useful models for identifying methods for breast cancer prediction and treatment. These studies in rats, combined with alternative animal models that more closely mimic advanced stages of breast cancer and/or human lifestyles, will further improve our understanding of this complex disease.

OUP accepted manuscript

Background

Methods

Results

Conclusion

Canine mammary tumors as a model for human disease

Animal models for examining human breast cancer (HBC) carcinogenesis have been extensively studied and proposed. With the recent advent of immunotherapy, significant attention has been focused on the dog as a model for human cancer. Dogs develop mammary tumors and other cancer types spontaneously with an intact immune system, which exhibit a number of clinical and molecular similarities to HBC. In addition to the spontaneous tumor presentation, the clinical similarities between human and canine mammary tumors (CMT) include the age at onset, hormonal etiology and course of the diseases. Furthermore, factors that affect the disease outcome, including tumor size, stage and lymph node invasion, are similar in HBC and CMT. Similarly, the molecular characteristics of steroid receptor, epidermal growth factor, proliferation marker, metalloproteinase and cyclooxygenase expression, and the mutation of the p53 tumor suppressor gene in CMT, mimic HBC. Furthermore, ductal carcinomas in situ in human and canine mammary glands are particularly similar in their pathological, molecular and visual characteristics. These CMT characteristics and their similarities to HBC indicate that the dog could be an excellent model for the study of human disease. These similarities are discussed in detail in the present review, and are compared with the in vitro and other in vivo animal models available.

Association of reproductive history with breast tissue characteristics and receptor status in the normal breast

Introduction

Reproductive history has been associated with breast cancer risk, but more knowledge of the underlying biological mechanisms is needed. Because of limited data on normal breast tissue from healthy women, we examined associations of reproductive history and established breast cancer risk factors with breast tissue composition and markers of hormone receptors and proliferation in a nested study within the Karolinska Mammography project for risk prediction for breast cancer (Karma).

Materials and methods

Tissues from 153 women were obtained by ultrasound-guided core needle biopsy as part of the Karma project. Immunohistochemical staining was used to assessed histological composition of epithelial, stromal and adipose tissue, epithelial and stromal oestrogen receptor (ER) and progesterone receptor (PR) status, and Ki-67 proliferation status. An individualised reproductive score including parity, number of pregnancies without birth, number of births, age at first birth, and duration of breastfeeding, was calculated based on self-reported reproductive history at the time of the Karma study entry. All analyses were adjusted for age and BMI.

Results

Cumulated reproductive score was associated with increased total epithelial content and greater expression of epithelial ER. Parity was associated with greater epithelial area, increased epithelial–stromal ratio, greater epithelial ER expression and a lower extent of stromal proliferation. Increasing numbers of pregnancies and births were associated with a greater epithelial area in the entire study set, which remained significant among postmenopausal women. Increasing numbers of pregnancies and births were also associated with a greater expression of epithelial ER among postmenopausal women. Longer duration of breastfeeding was associated with greater epithelial area and greater expression of epithelial PR both in the entire study set and among postmenopausal women. Breastfeeding was also positively associated with greater epithelial ER expression among postmenopausal women. Prior use of oral contraceptives was associated with lower epithelial–stromal ratio amongst all participants and among pre- and postmenopausal women separately.

Conclusion

Reproductive risk factors significantly influence the epithelial tissue compartment and expression of hormone receptors in later life. These changes remain after menopause. This study provides deeper insights of the biological mechanisms by which reproductive history influences epithelial area and expression of hormone receptors, and as a consequence the risk of breast cancer.

Electronic supplementary material

The online version of this article (10.1007/s10549-018-4768-0) contains supplementary material, which is available to authorized users.

Diagnosis of Fanconi Anaemia by ionising radiation- or mitomycin C-induced micronuclei

Fanconi Anaemia (FA) is an autosomal recessive disorder characterised by defects in DNA repair, associated with chromosomal instability and cellular hypersensitivity to DNA cross-linking agents such as mitomycin C (MMC). The FA repair pathway involves complex DNA repair mechanisms crucial for genomic stability. Deficiencies in DNA repair genes give rise to chromosomal radiosensitivity. FA patients have shown increased clinical radiosensitivity by exhibiting adverse normal tissue side-effects. The study aimed to investigate chromosomal radiosensitivity of homozygous and heterozygous carriers of FA mutations using three micronucleus (MN) assays. The G0 and S/G2MN assays are cytogenetic assays to evaluate DNA damage induced by ionising radiation in different phases of the cell cycle. The MMC MN assay detects DNA damage induced by a crosslinking agent in the G0 phase. Patients with a clinical diagnosis of FA and their parents were screened for the complete coding region of 20 FA genes. Blood samples of all FA patients and parents were exposed to ionising radiation of 2 and 4Gy. Chromosomal radiosensitivity was evaluated in the G0 and S/G2 phase. Most of our patients were homozygous for the founder mutation FANCG c.637_643delTACCGCC; p.(Tyr213Lysfs*6) while one patient was compound heterozygous for FANCG c.637_643delTACCGCC and FANCG c.1379G > A, p.(Gly460Asp), a novel missense mutation. Another patient was compound heterozygous for two deleterious FANCA mutations. In FA patients, the G0- and S/G2-MN assays show significantly increased chromosomal radiosensitivity and genomic instability. Moreover, chromosomal damage was significantly elevated in MMC treated FA cells. We also observed an increase in chromosomal radiosensitivity and genomic instability in the parents using 3 assays. The effect was significant using the MMC MN assay. The MMC MN assay is advantageous as it is less labour intense, time effective and has potential as a reliable alternative method for detecting FA patients from parents and controls.

Pregnancy and Breast Cancer

Breast cancer is the most commonly diagnosed type of cancer among women worldwide. The majority of breast cancers are sporadic and the etiology is not well understood. Several factors have been attributed to altering the risk of breast cancer. A full-term pregnancy is a crucial factor in altering the risk. Early full-term pregnancy has been shown to reduce the lifetime risk of breast cancer, while a later first full-term pregnancy increases breast cancer risk. Epidemiological and experimental data demonstrate that spontaneous or induced abortions do not significantly alter the risk of breast cancer. In this study, we briefly discuss the different types and stages of breast cancer, various risk factors, and potential mechanisms involved in early full-term pregnancy-induced protection against breast cancer. Understanding how early full-term pregnancy induces protection against breast cancer will help design innovative preventive and therapeutic strategies. This understanding can also help in the development of molecular biomarkers that can be of tremendous help in predicting the risk of breast cancer in the general population.

Development of 68Ga-SCN-DOTA-Capsaicin as an Imaging Agent Targeting Apoptosis and Cell Cycle Arrest in Breast Cancer

⁶⁸Ga-labeled capsaicin using a DOTA (1,4,7,10-tetraazocyclododecane-N,N',N″,N'″-tetraacetic acid) derivative [⁶⁸Ga-SCN-Benzyl(Bn)-DOTA-capsaicin] was studied for the diagnosis of breast cancers, such as MCF-7 and SK-BR-3. The standard compound, ⁶⁹Ga-SCN-Bn-DOTA-capsaicin, was also prepared and characterized by spectroscopic analysis. The binding affinity of ⁶⁸Ga-SCN-Bn-DOTA-capsaicin was evaluated by using breast cancer cell lines (MCF-7, SK-BR-3) and colon cancer cell (CT-26); the biodistribution was carried out by using MCF-7-bearing nude mice, after which the positron emission tomography (PET) images were obtained at different time intervals (15-120 minutes). ⁶⁸Ga-SCN-Bn-DOTA-capsaicin showed a cellular uptake of 0.93% Injected Dose (ID) after 30 minutes of incubation, whereas ⁶⁸Ga-SCN-Bn-DOTA showed a lower uptake of 0.25% ID. The tumor-to-blood ID/g% ratios increased and were found to be 0.49, 0.22, and 0.77 for 15, 30, and 60 minutes, respectively. The small-animal PET study showed that the uptake of ⁶⁸Ga-SCN-Bn-DOTA-capsaicin was higher in the tumor regions even at 30 minutes after injection. These results suggest that ⁶⁸Ga-SCN-Bn-DOTA-capsaicin is a potential targeting agent for PET imaging of MCF-7.

BMI, reproductive factors, and breast cancer molecular subtypes: A case-control study and meta-analysis

Background

The effects of body mass index (BMI) and reproductive factors may vary among breast cancer molecular subtypes, evidence of which is lacking in East Asia.

Methods

From 2002 to 2010, 1256 breast cancer patients and 1416 healthy women were recruited. Anthropometric and reproductive factors were collected from medical charts. Breast cancer subtype was defined by ER, PR, and HER2 status. Polytomous logistic regression was used to evaluate associations between risk factors and breast cancer subtypes, with subgroup analysis by menopausal status. A meta-analysis of relevant published studies in East Asia was also performed.

Results

In our case-control study, late menarche was negatively associated with luminal tumor risk (P_trend = 0.03). Higher BMI was associated with risk of both luminal and triple-negative tumors (P_trend<0.001). Late age at first live birth was associated with a 1.41- to 2.08-fold increased risk of all subtypes, while late menopause increased risk by 2.62–5.56 times. Heterogeneity of these associations was not detected for different menopausal statuses. The meta-analysis revealed a positive dose-response relationship between BMI and risk of both luminal and ER-PR- subtypes (P_trend<0.05). Early menarche and nulliparity increased luminal tumor risk by 1.39 and 1.26 times, respectively. Non-breastfeeding also increased the risk of all subtypes.

Conclusions

For East Asian women, overweight, late menopause, and lack of breastfeeding appear to increase risk of both luminal and ER−PR− tumors. Early menarche and nulliparity mainly impacted luminal tumor risk. These associations were not impacted by menopausal status.

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For East Asian women, overweight increases risk of both luminal and ER-PR- tumors.

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For East Asian women, early menarche increases luminal tumor risk.

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For East Asian women, nulliparity increases luminal tumor risk.

Age- and pregnancy-associated DNA methylation changes in mammary epithelial cells

Postnatal mammary gland development and differentiation occur during puberty and pregnancy. To explore the role of DNA methylation in these processes, we determined the genome-wide DNA methylation and gene expression profiles of CD24(+)CD61(+)CD29(hi), CD24(+)CD61(+)CD29(lo), and CD24(+)CD61(-)CD29(lo) cell populations that were previously associated with distinct biological properties at different ages and reproductive stages. We found that pregnancy had the most significant effects on CD24(+)CD61(+)CD29(hi) and CD24(+)CD61(+)CD29(lo) cells, inducing distinct epigenetic states that were maintained through life. Integrated analysis of gene expression, DNA methylation, and histone modification profiles revealed cell-type- and reproductive-stage-specific changes. We identified p27 and TGFβ signaling as key regulators of CD24(+)CD61(+)CD29(lo) cell proliferation, based on their expression patterns and results from mammary gland explant cultures. Our results suggest that relatively minor changes in DNA methylation occur during luminal differentiation compared with the effects of pregnancy on CD24(+)CD61(+)CD29(hi) and CD24(+)CD61(+)CD29(lo) cells.

Terminal duct lobular unit involution of the normal breast: implications for breast cancer etiology

BACKGROUND

Greater degrees of terminal duct lobular unit (TDLU) involution have been linked to lower breast cancer risk; however, factors that influence this process are poorly characterized.

METHODS

To study this question, we developed three reproducible measures that are inversely associated with TDLU involution: TDLU counts, median TDLU span, and median acini counts/TDLU. We determined factors associated with TDLU involution using normal breast tissues from 1938 participants (1369 premenopausal and 569 postmenopausal) ages 18 to 75 years in the Susan G. Komen Tissue Bank at the Indiana University Simon Cancer Center. Multivariable zero-inflated Poisson models were used to estimate relative risks (RRs) and 95% confidence intervals (95% CIs) for factors associated with TDLU counts, and multivariable ordinal logistic regression models were used to estimate odds ratios (ORs) and 95% CIs for factors associated with categories of median TDLU span and acini counts/TDLU.

RESULTS

All TDLU measures started declining in the third age decade (all measures, two-sided P trend ≤ .001); and all metrics were statistically significantly lower among postmenopausal women. Nulliparous women demonstrated lower TDLU counts compared with uniparous women (among premenopausal women, RR = 0.79, 95% CI = 0.73 to 0.85; among postmenopausal, RR = 0.67, 95% CI = 0.56 to 0.79); however, rates of age-related TDLU decline were faster among parous women. Other factors were related to specific measures of TDLU involution.

CONCLUSION

Morphometric analysis of TDLU involution warrants further evaluation to understand the pathogenesis of breast cancer and assessing its role as a progression marker for women with benign biopsies or as an intermediate endpoint in prevention studies.

Genome-wide DNA methylation profiling reveals parity-associated hypermethylation of FOXA1

Early pregnancy in women by the age of 20 is known to have a profound effect on reduction of lifelong breast cancer risk as compared to their nulliparous counterparts. Additional pregnancies further enhance the protection against breast cancer development. Nationwide trend of delayed pregnancy may contribute to the recently reported increase in the incidence of advanced breast cancer among young women in this country. The underlying mechanism for the parity-associated reduction of breast cancer risk is not clearly understood. The purpose of the current study is to use whole-genome DNA methylation profiling to explore a potential association between parity and epigenetic changes in breast tissue from women with early parity and nulliparity. Breast tissue was collected from age-matched cancer-free women with early parity (age < 20; n = 15) or nulliparity (n = 13). The methyl-CpG binding domain-based capture-sequencing technology was used for whole-genome DNA methylation profiling. Potential parity-associated hypermethylated genes were further verified by locus-specific pyrosequencing, using an expanded cohort of parous (n = 19) and nulliparous (n = 16) women that included the initial samples used in the global analysis. Our study identified six genes that are hypermethylated in the parous group (P < 0.05). Pyrosequencing confirmed parity-associated hypermethylation at multiple CpG islands of the FOXA1 gene, which encodes a pioneer factor that facilitates chromatin binding of estrogen receptor α. Our work identifies several potential methylation biomarkers for parity-associated breast cancer risk assessment. In addition, the results are consistent with the notion that parity-associated epigenetic silencing of FOXA1 contributes to long-term attenuation of the estrogenic impact on breast cancer development.

Postpartum breast involution reveals regression of secretory lobules mediated by tissue-remodeling

Introduction

A postpartum diagnosis of breast cancer is an independent predictor of metastases, however the reason is unknown. In rodents, the window of postpartum mammary gland involution promotes tumor progression, suggesting a role for breast involution in the poor prognosis of human postpartum breast cancers. Rodent mammary gland involution is characterized by the programmed elimination of the secretory lobules laid down in preparation for lactation. This tissue involution process involves massive epithelial cell death, stromal remodeling, and immune cell infiltration with similarities to microenvironments present during wound healing and tumor progression. Here, we characterize breast tissue from premenopausal women with known reproductive histories to determine the extent, duration and cellular mechanisms of postpartum lobular involution in women.

Methods

Adjacent normal breast tissues from premenopausal women (n = 183) aged 20 to 45 years, grouped by reproductive categories of nulliparous, pregnant and lactating, and by time since last delivery were evaluated histologically and by special stain for lobular area, lobular type composition, apoptosis and immune cell infiltration using computer assisted quantitative methods.

Results

Human nulliparous glands were composed dominantly of small (approximately 10 acini per lobule) and medium (approximately 35 acini per lobule) sized lobules. With pregnancy and lactation, a >10 fold increase in breast epithelial area was observed compared to nulliparous cases, and lactating glands were dominated by mature lobules (>100 acini per lobule) with secretory morphology. Significant losses in mammary epithelial area and mature lobule phenotypes were observed within 12 months postpartum. By 18 months postpartum, lobular area content and lobule composition were indistinguishable from nulliparous cases, data consistent with postpartum involution facilitating regression of the secretory lobules developed in preparation for lactation. Analyses of apoptosis and immune cell infiltrate confirmed that human postpartum breast involution is characterized by wound healing-like tissue remodeling programs that occur within a narrowed time frame.

Conclusions

Human postpartum breast involution is a dominant tissue-remodeling process that returns the total lobular area of the gland to a level essentially indistinguishable from the nulliparous gland. Further research is warranted to determine whether the normal physiologic process of postpartum involution contributes to the poor prognosis of postpartum breast cancer.

Molecular pathways involved in pregnancy-induced prevention against breast cancer

Pregnancy produces a protective effect against breast cancer in women who had their first full term pregnancy (FTP) in their middle twenties. The later in life the first delivery occurs, the higher the risk of breast cancer development. Also, transiently during the postpartum period, the risk of developing breast cancer increases. This transient increased risk is taken over by a long-lasting protective period. The genomic profile of parous women has shown pregnancy induces a long-lasting "genomic signature" that explains the preventive effect on breast cancer. This signature reveals that chromatin remodeling is the driver of the differentiation process conferred by FTP. The chromatin remodeling process may be the ultimate step mediating the protection of the breast against developing breast cancer in post-menopausal years.

High male chimerism in the female breast shows quantitative links with cancer

Clinical observations suggest that pregnancy provides protection against cancer. The mechanisms involved, however, remain unclear. Fetal cells are known to enter the mother's circulation during pregnancy and establish microchimerism. We investigated if pregnancy-related embryonic/fetal stem cell integration plays a role in breast cancer. A high-sensitivity Y-chromosome assay was developed to trace male allogeneic cells (from male fetus) in females. Fixed-embedded samples (n = 206) from both normal and breast cancer patients were screened for microchimerism. The results were combined with matching clinicopathological and histological parameters and processed statistically. The results show that in our samples (182 informative) more than half of healthy women (56%) carried male cells in their breast tissue for decades (n = 68), while only one out of five in the cancer sample pool (21%) (n = 114) (odds ratio = 4.75, CI at 95% 2.34-9.69; p = 0.0001). The data support the notion that a biological link may exist between chimerism and tissue-integrity. The correlation, however, is non-linear, since male microchimerism in excess ("hyperchimerism") is also involved in cancer. The data suggest a link between hyperchimerism and HER2-type cancers, while decreased chimerism ("hypochimerism") associates with ER/PR-positive (luminal-type) breast cancers. Chimerism levels that correlate with protection appear to be non-random and share densities with the mammary progenitor components of the stem cell lineage in the breast. The results suggest that protection may involve stem/progenitor level interactions and implicate novel quantitative mechanisms in chimerism biology.

Progesterone--promoter or inhibitor of breast cancer

Based on the results of a French cohort of postmenopausal women, it has been claimed that micronized progesterone does not enhance breast cancer risk. The impact of reproductive factors on breast cancer risk and a high prevalence of occult breast carcinomas at the time of menopause suggest an involvement of endogenous progesterone in the development of breast cancer. High mammographic density in the luteal phase and during treatment with estrogen/progestogen combinations reflect a change in the composition of mammary stroma and an increased water accumulation in the extracellular matrix which is caused by hygroscopic hyaluronan-proteoglycan aggregates. Proteoglycans are also involved in the regulation of proliferation, migration, and differentiation of epithelial cells and angiogenesis, and may influence malignant transformation of breast cells and progression of tumors. Reports on a lack of effect of estrogen/progesterone therapy on breast cancer risk may be rooted in a selective prescription to overweight women and/or to the very low progesterone serum levels after oral administration owing to a strong inactivation rate. The contradictory results concerning the proliferative effect of progesterone may be associated with a different local metabolism in normal compared to malignant breast tissue. Similar to other progestogens, hormone replacement therapy with progesterone seems to promote the development of breast cancer, provided that the progesterone serum levels have reached the threshold for endometrial protection.

Breast arterial calcification is associated with reproductive factors in asymptomatic postmenopausal women

OBJECTIVE

The etiology of breast arterial calcification (BAC) is not well understood. We examined reproductive history and cardiovascular disease (CVD) risk factor associations with the presence of detectable BAC in asymptomatic postmenopausal women.

METHODS

Reproductive history and CVD risk factors were obtained in 240 asymptomatic postmenopausal women from a community-based research study who had a screening mammogram within 2 years of their participation in the study. The mammograms were reviewed for the presence of detectable BAC. Age-adjusted logistic regression models were fit to assess the association between each risk factor and the presence of BAC. Multiple variable logistic regression models were used to identify the most parsimonious model for the presence of BAC.

RESULTS

The prevalence of BAC increased with increased age (p < 0.0001). The most parsimonious logistic regression model for BAC presence included age at time of examination, increased parity (p = 0.01), earlier age at first birth (p = 0.002), weight, and an age-by-weight interaction term (p = 0.004). Older women with a smaller body size had a higher probability of having BAC than women of the same age with a larger body size.

CONCLUSIONS

The presence or absence of BAC at mammography may provide an assessment of a postmenopausal woman's lifetime estrogen exposure and indicate women who could be at risk for hormonally related conditions.

Reproductive factors and breast cancer risk in relation to hormone receptor and menopausal status in Japanese women

The associations between menstrual and reproductive factors and breast cancer risk in relation to estrogen/progesterone receptor (ER/PgR) status have been unclear in Japanese women. This case-control study evaluated these associations, overall and separately, by menopausal status. A total of 1092 breast cancer cases and 3160 controls were selected from among female patients aged 30 years and over admitted to a single hospital in Miyagi Prefecture between 1997 and 2009. The receptor status distribution among the cases (missing: 8.4%) was 571 ER+/PgR+, 133 ER+/PgR-, 24 ER-/PgR+ and 271 ER-/PgR-. Menstrual and reproductive factors were assessed using a self-administered questionnaire. Polytomous logistic regression and tests for heterogeneity across ER+/PgR+ and ER-/PgR- were conducted. Later age at menarche was significantly associated with a decreased risk of both ER+/PgR+ and ER-/PgR- cancer among women overall (P(trend) = 0.0016 for ER+/PgR+; P(trend) = 0.015 for ER-/PgR-) and among postmenopausal women (P(trend) = 0.012 for ER+/PgR+; P(trend) = 0.0056 for ER-/PgR-). Nulliparity was associated with an increased risk of ER+/PgR+, but not ER-/PgR- cancer among women overall (P(heterogeneity) = 0.019) and among postmenopausal women (odds ratio for ER+/PgR+ = 2.56, 95% confidence interval = 1.61-4.07; P(heterogeneity) = 0.0095). A longer duration of breastfeeding tended to be associated with a decreased risk in all subtypes among women overall. Later age at menarche has a protective effect against both ER+/PgR+ and ER-/PgR- cancer. However, parity might impact differently on various subtypes of breast cancer. Further studies are needed to clarify the etiology of the rare ER+/PgR- and ER-/PgR+ cancer subtypes.

Morinda citrifolia (Noni) Juice Augments Mammary Gland Differentiation and Reduces Mammary Tumor Growth in Mice Expressing the Unactivated c-erbB2 Transgene

Morinda citrifolia (noni) is reported to have many beneficial properties, including on immune, inflammatory, quality of life, and cancer endpoints, but little is known about its ability to prevent or treat breast cancer. To test its anticancer potential, the effects of Tahitian Noni Juice (TNJ) on mammary carcinogenesis were examined in MMTV-neu transgenic mice. Mammary tumor latency, incidence, multiplicity, and metastatic incidence were unaffected by TNJ treatment, which suggests that it would not increase or decrease breast cancer risk in women taking TNJ for its other benefits. However, noni may be useful to enhance treatment responses in women with existing HER2/neu breast cancer since TNJ resulted in significant reductions in tumor weight and volume and in longer tumor doubling times in mice. Remarkably, its ability to inhibit the growth of this aggressive form of cancer occurred with the mouse equivalent of a recommended dose for humans (<3 oz/day). A 30-day treatment with TNJ also induced significant changes in mammary secondary ductule branching and lobuloalveolar development, serum progesterone levels, and estrous cycling. Additional studies investigating TNJ-induced tumor growth suppression and modified reproductive responses are needed to characterize its potential as a CAM therapy for women with and without HER2⁺ breast cancer.

The Susan G. Komen for the Cure Tissue Bank at the IU Simon Cancer Center: a unique resource for defining the "molecular histology" of the breast

"Molecular histology" of the breast may be conceptualized as encompassing the normative ranges of histologic structure and marker expression in normal breast tissues in relation to a woman's age and life experiences. Studies of molecular histology can aid our understanding of early events in breast carcinogenesis and provide data for comparison with diseased breast tissues. Until recently, lack of epidemiologically annotated, optimally prepared normal breast tissues obtained from healthy women presented a barrier to breast cancer research. The Komen Tissue Bank at Indiana University (Indianapolis, IN) is a unique biorepository that was developed to overcome this limitation. The Bank enrolls healthy donors who provide questionnaire data, blood, and up to four breast biopsies, which are prepared as both formalin-fixed, paraffin-embedded and frozen tissues. The resource is accessible to researchers worldwide through a proposal submission, review, and approval process. As of November 2010, the Bank had collected specimens and information from 1,174 donors. In this review, we discuss the importance of studying normal breast tissues, assess the strengths and limitations of studying normal tissues obtained from different sources, and summarize the features of the Komen Tissue Bank. As research projects are completed, results will be posted on the Bank's website.

Mouse models of estrogen receptor-positive breast cancer

Breast cancer is the most frequent malignancy and second leading cause of cancer-related deaths among women. Despite advances in genetic and biochemical analyses, the incidence of breast cancer and its associated mortality remain very high. About 60 – 70% of breast cancers are Estrogen Receptor alpha (ER-α) positive and are dependent on estrogen for growth. Selective estrogen receptor modulators (SERMs) have therefore provided an effective targeted therapy to treat ER-α positive breast cancer patients. Unfortunately, development of resistance to endocrine therapy is frequent and leads to cancer recurrence. Our understanding of molecular mechanisms involved in the development of ER-α positive tumors and their resistance to ER antagonists is currently limited due to lack of experimental models of ER-α positive breast cancer. In most mouse models of breast cancer, the tumors that form are typically ER-negative and independent of estrogen for their growth. However, in recent years more attention has been given to develop mouse models that develop different subtypes of breast cancers, including ER-positive tumors. In this review, we discuss the currently available mouse models that develop ER-α positive mammary tumors and their potential use to elucidate the molecular mechanisms of ER-α positive breast cancer development and endocrine resistance.

Effect of infertility treatment and pregnancy-related hormones on breast cell proliferation in vitro

BACKGROUND

Breast cancer development involves a series of mutations in a heterogeneous group of proto-oncogenes/tumor suppressor genes that alter mammary cells to create a microenvironment permissive to tumorigenesis. Exposure to hormones during infertility treatment may have a mutagenic effect on normal mammary epithelial cells, high-risk breast lesions and early-stage breast cancers. Our goal was to understand the association between infertility treatment and normal and cancerous breast cell proliferation.

METHODS

MCF-10A normal mammary cells and the breast cancer cell lines MCF-7 [estrogen receptor (ER)-positive, well differentiated] and HCC 1937 (ER-negative, aggressive, BRCA1 mutation) were treated with the weak ER activator clomiphene citrate and hormones that are increased during infertility treatment. Direct effects of treatment on cell proliferation and colony growth were determined.

RESULTS

While clomiphene citrate had no effect on MCF-10A cells or MCF-7 breast cancer cells, it decreased proliferation of HCC 1937 versus untreated cells (P= 0.003). Estrogen had no effect on either MCF-10A or HCC 1937 cells but, as expected, increased cell proliferation (20-100 nM; P≤0.002) and colony growth (10-30 nM; P< 0.0001) of MCF-7 cells versus control. Conversely, progesterone decreased both proliferation (P= 0.001) and colony growth (P= 0.01) of MCF-10A cells, inhibited colony size of MCF-7 cells (P= 0.01) and decreased proliferation of HCC 1937 cells (P= 0.008) versus control. hCG (100 mIU/ml) decreased both proliferation (P ≤ 0.01) and colony growth (P ≤ 0.002) of all three cell lines.

CONCLUSIONS

Although these data are preclinical, they support possible indirect estrogenic effects of infertility regimens on ER-positive breast cancer cells and validate the potential protective effect of pregnancy-related exposure to hCG.

Pregnancy-induced changes in breast cancer risk

Breast cancer is the malignant disease most frequently diagnosed in women of all races and nationalities. Since the 1970s the worldwide incidence of this disease has increased 30-40% in postmenopausal women, in whom, paradoxically, the risk of developing breast cancer is significantly reduced by an early first full term pregnancy (FTP) as compared to nulliparous and late parous women. Although the cause of breast cancer is not known, the mechanisms mediating the protection conferred by an early FTP have been identified to reside in the breast itself, and to be modulated by endogenous and environmental exposures that might negatively affect this organ during specific windows in its development that extend from prenatal life until the first pregnancy. Soon after conception the embryo initiates the production of human chorionic gonadotropin (hCG), the glycoprotein hormone that is diagnostic of pregnancy. HCG in conjunction with ovarian steroid hormones primes the hypothalamic neuroendocrine system for maintaining the pregnancy. Higher levels of hCG during the first trimester of pregnancy have been associated with a reduction in maternal breast cancer incidence after age 50. In preclinical studies it has been demonstrated that both FTP and hCG treatment of virgin rats prevent the development of chemically-induced mammary tumors, a phenomenon mediated by the differentiation of the mammary gland epithelial cells prior to carcinogen exposure. Complete differentiation proceeds through complex morphological, physiological and molecular changes that occur during pregnancy and lactation, that ultimately result in increased DNA repair capabilities of the mammary epithelium, activation of genes controlling differentiation and programmed cell death and imprinting in the breast epithelium a specific and permanent genomic signature of pregnancy. This signature is indicative of a reduced breast cancer risk and serves as a molecular biomarker of differentiation for evaluating the potential use of chemopreventive agents.

Characterization of a genomic signature of pregnancy identified in the breast

The objective of this study was to comprehensively compare the genomic profiles in the breast of parous and nulliparous postmenopausal women to identify genes that permanently change their expression following pregnancy. The study was designed as a two-phase approach. In the discovery phase, we compared breast genomic profiles of 37 parous with 18 nulliparous postmenopausal women. In the validation phase, confirmation of the genomic patterns observed in the discovery phase was sought in an independent set of 30 parous and 22 nulliparous postmenopausal women. RNA was hybridized to Affymetrix HG_U133 Plus 2.0 oligonucleotide arrays containing probes to 54,675 transcripts, scanned and the images analyzed using Affymetrix GCOS software. Surrogate variable analysis, logistic regression, and significance analysis of microarrays were used to identify statistically significant differences in expression of genes. The false discovery rate (FDR) approach was used to control for multiple comparisons. We found that 208 genes (305 probe sets) were differentially expressed between parous and nulliparous women in both discovery and validation phases of the study at an FDR of 10% and with at least a 1.25-fold change. These genes are involved in regulation of transcription, centrosome organization, RNA splicing, cell-cycle control, adhesion, and differentiation. The results provide initial evidence that full-term pregnancy induces long-term genomic changes in the breast. The genomic signature of pregnancy could be used as an intermediate marker to assess potential chemopreventive interventions with hormones mimicking the effects of pregnancy for prevention of breast cancer.

Aryl hydrocarbon receptor activation during pregnancy, and in adult nulliparous mice, delays the subsequent development of DMBA-induced mammary tumors

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD), the prototypic ligand for the aryl hydrocarbon receptor (AhR), promotes tumor formation in some model systems. However, with regard to breast cancer, epidemiological and animal studies are inconclusive as to whether exposure increases tumor incidence or may instead be protective. We have previously reported that mice exposed to TCDD during pregnancy have impaired differentiation of mammary tissue, including decreased branching and poor development of lobuloalveolar structures. Because normal pregnancy-induced mammary differentiation may protect against subsequent neoplastic transformation, we hypothesized that TCDD-treated mice would be more susceptible to chemical carcinogenesis after parturition. To test this, mice were treated with TCDD or vehicle during pregnancy. Four weeks later, 7,12-dimethylbenz[a]anthracene (DMBA) was administered to induce mammary tumor formation. Contrary to our hypothesis, TCDD-exposed parous mice showed a 4-week delay in tumor formation relative to controls, and they had a lower tumor incidence throughout the 27-week time course. The same results were obtained in nulliparous mice given TCDD and DMBA on the same schedule. We next addressed whether the delayed tumor incidence was a reflection of decreased tumor initiation, by testing the formation of DMBA-DNA adducts and preneoplastic lesions, induction of cytochrome P450s, and cell proliferation. None of these markers of tumor initiation differed between vehicle- and TCDD-treated animals. The expression of CXCL12 and CXCR4 was also measured to address their possible role in tumorigenesis. Taken together, our results suggest that AhR activation by TCDD slows the promotion of preneoplastic lesions to overt mammary tumors.

Cancer protection of soy resembles cancer protection during pregnancy

It has been established that carrying a pregnancy to full-term at an early age can protect against contracting cancer by up to 50% in later life. The trophoblast theory of cancer states that trophoblast and cancer tissue are very similar. New findings suggest that the loss of fetal cells during pregnancy resemble those cells responsible for causing metastasis in cancer. Fetal cells and spreading cancer cells are highly proliferative. They are similar to stem cells, exhibiting no or low hormone receptor expression, and require a hormone receptor independent mechanism for control. Control of membrane stability during pregnancy is of vital importance for a successful pregnancy and is mediated by androstenediol and 2-methoxyestradiol. 2-Methoxyestradiol has no hormone receptor affinity and elicits strong anticancer effects particularly against cancer stem cells and fetal cells, for which currently no treatment has yet been established. There is a discussion whether pregnancy reduces cancer stem cells in the breast. Soy isoflavones are structurally similar to both hormones, and elicit strong anticancer effects and antiangiogenesis via inhibition of NF-κB, even in hormone receptor independent breast cancers seen in epidemiologic studies. The trophoblast theory of cancer could help to explain why soy baby nutrition formulas have no effect on baby physiology, other than the nutritional aspect, although soy elicits many effects on the adult immune system. To survive the immune system of the mother, the immune system of the fetus has to be separated; otherwise, the reduction of the immune system in the mother, a necessary feature for the blastocyst to grow, would immediately reduce the immunity for the fetus and endanger its survival. Similar to a fetus, newly born babies show immune insensitive to Th1 and Th2 cytokines, which are necessary and crucial for regulating the immune system of the mother, thus raising the risk of the baby of developing allergies and neurodermatitis. Gene expression studies in vitro as well as in circulating tumor cells from patients consuming a fermented soy product support the antiangiogenic as well as antiproliferative effects of soy.

Risk factors according to estrogen receptor status of breast cancer patients in Trivandrum, South India

Estrogen receptor (ER) status is an important biomarker in defining subtypes of breast cancer differing in antihormonal therapy response, risk factors and prognosis. However, little is known about association of ER status with various risk factors in the developing world. Our case-control study done in Kerala, India looked at the associations of ER status and risk factors of breast cancer. From 2002 to 2005, 1,208 cases and controls were selected at the Regional Cancer Center (RCC), Trivandrum, Kerala, India. Information was collected using a standardized questionnaire, and 3-way analyses compared ER+/ER- cases, ER+ cases/controls and ER- cases/controls using unconditional logistic regression to calculate odds ratios and 95% confidence intervals. The proportion of ER- cases was higher (64.1%) than ER+ cases. Muslim women were more likely to have ER- breast cancer compared to Hindus (OR = 1.48, 95% CI = 1.09, 2.02), an effect limited to premenopausal group (OR = 1.87, 95% CI = 1.26, 2.77). Women with higher socioeconomic status were more likely to have ER+ breast cancer (OR = 1.48, 95% CI = 1.11, 1.98). Increasing BMI increased likelihood of ER- breast cancer in premenopausal women (p for trend < 0.001). Increasing age of marriage was positively associated with both ER+ and ER- breast cancer. Increased breastfeeding and physical activity were in general protective for both ER+ and ER- breast cancer. The findings of our study are significant in further understanding the relationship of ER status and risk factors of breast cancer in the context of the Indian subcontinent.

Breast cancer prevention

We have developed a new approach for breast cancer prevention, capitalizing in the preventive effect of early first full-term pregnancy, hormonally induced differentiation and our ability to identify specific genomic signatures that allow us to predict risk reduction. Early pregnancy imprints in the breast permanent genomic changes or a 'signature' that reduces the susceptibility of this organ to cancer. At cellular level, what we have achieved is the shifting of the Stem Cell 1 population, highly susceptible to cancer, to a population of Stem Cell 2 that is refractory to carcinogenesis. In a case-control study, we have compared the gene expression profile in normal breast tissue from nulliparous and parous postmenopausal women with (case) and without (control) breast cancer. We have determined that early first full-term pregnancy induces a specific genomic signature in the postmenopausal breast that is the biomarker for the Stem cell 2. The Stem cell 2 contains specific genes controlling transcription, RNA processing, immune response, apoptosis and DNA repair. We have further detected in the plasma, using an ELISA assay, the proteins coded by the gene signature. We are developing clinical trials to demonstrate the proof of the principle that r-hCG can induce in the human breast a genomic signature of the Stem cell 2. This is a concept that challenges the currently available chemopreventive agents that need to be given for extended periods for maintaining the suppression of a specific metabolic pathway or the abrogation of the function of an organ.

Normal breast tissue implanted into athymic nude mice identifies biomarkers of the effects of human pregnancy levels of estrogen

We have generated a novel model system for the study of estrogen intervention in normal breast tissue. Nulliparous human breast tissue was implanted into immunocompromised nude mice and treated with high-dose estrogen to simulate the effects of pregnancy. Treatment of mice with human mid-pregnancy levels of 17beta-estradiol for a period of 4 weeks was followed by 4 weeks of withdrawal to mimic involution. Gene expression in the xenograft tissue was then analyzed by real-time reverse transcription-PCR to identify differences between treated and control tissues. Ten genes previously identified as altered by pregnancy in rodent models were found to be differentially expressed in human breast tissue with a > or =1.8-fold up-regulation of CDC42, TGFbeta3, DCN, KRT14, LTF, and AREG and a > or =0.7-fold down-regulation of STAT1, CTGF, IGF1, and VAMP1. Immunohistochemical analysis of archival paraffin-embedded adult premenopausal human breast tissue specimens identified a significantly lower level of expression of STAT1 (P < 0.05, Mann-Whitney U test) in parous compared with age-matched nulliparous tissue (median of 24% compared with 42% epithelial cells positive). We conclude that many of the pregnancy-induced breast cancer-protective changes observed in rodent models also occur in human breast tissue following intervention using human pregnancy levels of estrogen and that STAT1 expression is a potential biomarker of parity-induced breast cancer protection in the human breast.

Human chorionic gonadotropin and alpha-fetoprotein concentrations in pregnancy and maternal risk of breast cancer: a nested case-control study

Pregnancy hormones are believed to be involved in the protection against breast cancer conferred by pregnancy. The authors explored the association of maternal breast cancer with human chorionic gonadotropin (hCG) and alpha-fetoprotein (AFP). In 2001, a case-control study was nested within the Northern Sweden Maternity Cohort, an ongoing study in which blood samples have been collected from first-trimester pregnant women since 1975. Cases (n = 210) and controls (n = 357) were matched for age, parity, and date of blood donation. Concentrations of hCG and AFP were measured by immunoassay. No overall significant association of breast cancer with either hCG or AFP was observed. However, women with hCG levels in the top tertile tended to be at lower risk of breast cancer than women with hCG levels in the lowest tertile in the whole study population and in subgroups of age at sampling, parity, and age at cancer diagnosis. A borderline-significant decrease in risk with high hCG levels was observed in women who developed breast cancer after the median lag time to cancer diagnosis (> or =14 years; odds ratio = 0.53, 95% confidence interval: 0.27, 1.03; P = 0.06). These findings, though very preliminary, are consistent with a possible long-term protective association of breast cancer risk with elevated levels of circulating hCG in the early stages of pregnancy.

Breast development, hormones and cancer

Breast cancer originates in undifferentiated terminal structures of the mammary gland. The terminal ducts of the Lob 1 of the human female breast, which are the sites of origin of ductal carcinomas, are at their peak of cell replication during early adulthood, a period during which the breast is more susceptible to carcinogenesis. The susceptibility of Lob 1 to undergo neoplastic transformation has been confirmed by in vitro studies, which have shown that this structure has the highest proliferative activity, estrogen receptor content and rate of carcinogen binding to the DNA. The higher incidence of breast cancer observed in nulliparous women supports this concept, whereas the protection afforded by early full-term pregnancy in women could be explained by the higher degree of differentiation of the mammary gland at the time in which an etiologic agent or agents act.

Implications of the cancer stem-cell hypothesis for breast cancer prevention and therapy

Recent research in breast biology has provided support for the cancer stem-cell hypothesis. Two important components of this hypothesis are that tumors originate in mammary stem or progenitor cells as a result of dysregulation of the normally tightly regulated process of self-renewal. As a result, tumors contain and are driven by a cellular subcomponent that retains key stem-cell properties including self-renewal, which drives tumorigenesis and differentiation that contributes to cellular heterogeneity. Advances in stem-cell technology have led to the identification of stem cells in normal and malignant breast tissue. The study of these stem cells has helped to elucidate the origin of the molecular complexity of human breast cancer. The cancer stem-cell hypothesis has important implications for early detection, prevention, and treatment of breast cancer. Both hereditary and sporadic breast cancers may develop through dysregulation of stem-cell self-renewal pathways. These aberrant stem cells may provide targets for the development of cancer prevention strategies. Furthermore, because breast cancer stem cells may be highly resistant to radiation and chemotherapy, the development of more effective therapies for this disease may require the effective targeting of this cell population.

Epidemiology of basal-like breast cancer

Risk factors for the newly identified "intrinsic" breast cancer subtypes (luminal A, luminal B, basal-like and human epidermal growth factor receptor 2-positive/estrogen receptor-negative) were determined in the Carolina Breast Cancer Study, a population-based, case-control study of African-American and white women. Immunohistochemical markers were used to subtype 1,424 cases of invasive and in situ breast cancer, and case subtypes were compared to 2,022 controls. Luminal A, the most common subtype, exhibited risk factors typically reported for breast cancer in previous studies, including inverse associations for increased parity and younger age at first full-term pregnancy. Basal-like cases exhibited several associations that were opposite to those observed for luminal A, including increased risk for parity and younger age at first term full-term pregnancy. Longer duration breastfeeding, increasing number of children breastfed, and increasing number of months breastfeeding per child were each associated with reduced risk of basal-like breast cancer, but not luminal A. Women with multiple live births who did not breastfeed and women who used medications to suppress lactation were at increased risk of basal-like, but not luminal A, breast cancer. Elevated waist-hip ratio was associated with increased risk of luminal A in postmenopausal women, and increased risk of basal-like breast cancer in pre- and postmenopausal women. The prevalence of basal-like breast cancer was highest among premenopausal African-American women, who also showed the highest prevalence of basal-like risk factors. Among younger African-American women, we estimate that up to 68% of basal-like breast cancer could be prevented by promoting breastfeeding and reducing abdominal adiposity.

Full-term pregnancy induces a specific genomic signature in the human breast

Breast cancer risk has traditionally been linked to nulliparity or late first full-term pregnancy, whereas young age at first childbirth, multiparity, and breast-feeding are associated with a reduced risk. Early pregnancy confers protection by inducing breast differentiation, which imprints a specific and permanent genomic signature in experimental rodent models. For testing whether the same phenomenon was detectable in the atrophic breast of postmenopausal parous women, we designed a case-control study for the analysis of the gene expression profile of RNA extracted from epithelial cells microdissected from normal breast tissues obtained from 18 parous and 7 nulliparous women free of breast pathology (controls), and 41 parous and 8 nulliparous women with history of breast cancer (cases). RNA was hybridized to cDNA glass microarrays containing 40,000 genes; arrays were scanned and the images were analyzed using ImaGene software version 4.2. Normalization and statistical analysis were carried out using Linear Models for Microarrays and GeneSight software for hierarchical clustering. The parous control group contained 2,541 gene sequences representing 18 biological processes that were differentially expressed in comparison with the other three groups. Hierarchical clustering of these genes revealed that the combined parity/absence of breast cancer data generated a distinct genomic profile that differed from those of the breast cancer groups, irrespective of parity history, and from the nulliparous cancer-free group, which has been traditionally identified as a high-risk group. The signature that identifies those women in whom parity has been protective will serve as a molecular biomarker of differentiation for evaluating the potential use of preventive agents.

Heightened risk of breast cancer following pregnancy: could lasting systemic immune alterations contribute?

The protective effect of having a first full-term pregnancy (FFTP) at a younger age on women's lifetime risk of breast cancer is well known. Less appreciated is the increased risk seen in the years immediately following pregnancy. This adverse effect is more pronounced and more prolonged in women with later age at FFTP. The mechanisms responsible for this increased risk are still poorly understood. In the present paper, we put forward the hypothesis that the marked peripheral immune changes induced by pregnancy may account for these effects. We highlight immune changes that characterize the unique immune state of pregnancy (a combination of cellular immunosuppression and enhanced inflammatory response), note the resemblance of these changes to cancer escape mechanisms, and discuss why such immune changes may be critical for the development of breast cancer following pregnancy. We further support this idea by initial findings from our own laboratory that the age at FFTP is negatively related to natural killer cell cytotoxicity many years later and propose possible models for the kinetics of the immune changes during and following pregnancy. The effect of age at FFTP on the immune function is currently understudied. Its potential relevance to the development of breast cancer stresses the need for further research.

Modelling breast cancer: one size does not fit all

Breast cancer is not a single disease, but is instead a collection of diseases that have distinct histopathological features, genetic and genomic variability, and diverse prognostic outcomes. Thus, no individual model would be expected to completely recapitulate this complex disease. Here, the models commonly used to investigate breast cancer including cell lines, xenografts and genetically engineered mice, are discussed to help address the question: what is the most powerful way to investigate this heterogeneous disease?

Timing of Dietary Estrogenic Exposures and Breast Cancer Risk

The same dietary component, such as fat or phytochemicals in plant foods, can have an opposite effect on breast cancer risk if exposed in utero through a pregnant mother or at puberty. Dietary exposures during pregnancy often have similar effects on breast cancer risk among mothers and their female offspring. High fat intake and obesity are illustrative examples: excessive pregnancy weight gain that increases high birth weight is associated with increased breast cancer risk among mothers and daughters. High body weight during childhood is inversely linked to later breast cancer risk. The main reason why the age when dietary exposures occur determines their effect on breast cancer risk likely reflects the extensive programming of the mammary gland during fetal life and subsequent reprogramming at puberty and pregnancy. Programming is a series of epigenetic/transcriptional modifications in gene expression that can be influenced by changes in the hormonal environment induced, for example, by diet. Because epigenetic modifications are inherited by daughter cells, they can persist throughout life if they occur in mammary stem cells or uncommitted mammary myoepithelial or luminal progenitor cells. Our results indicate that the estrogen receptor (ER), mitogen-activated protein kinase (MAPK), and the tumor suppressors BRCA1, p53, and caveolin-1 are among the genes affected by diet-induced alterations in programming/reprogramming. Consequently, mammary gland morphology may be altered in a manner that increases or reduces susceptibility to malignant transformation, including an increase/reduction in cell proliferation, differentiation, and survival, or in the number of terminal end buds (TEBs) or pregnancy-induced mammary epithelial cells (PI-MECs) that are the sites where breast cancer is initiated. Thus, dietary exposures during pregnancy and puberty may play an important role in determining later risk by inducing epigenetic changes that modify vulnerability to breast cancer.