Reproductive factors and subtypes of breast cancer defined by hormone receptor and histology

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.

Breast cancer prognosis through the use of multi-modal classifiers: current state of the art and the way forward

We present a survey of the current state-of-the-art in breast cancer detection and prognosis. We analyze the evolution of Artificial Intelligence-based approaches from using just uni-modal information to multi-modality for detection and how such paradigm shift facilitates the efficacy of detection, consistent with clinical observations. We conclude that interpretable AI-based predictions and ability to handle class imbalance should be considered priority.

Is There a Special Role for Ovarian Hormones in the Pathogenesis of Lobular Carcinoma?

Lobular carcinoma represent the most common special histological subtype of breast cancer, with the majority classed as hormone receptor positive. Rates of invasive lobular carcinoma in postmenopausal women have been seen to increase globally, while other hormone receptor-positive breast cancers proportionally have not followed the same trend. This has been linked to exposure to exogenous ovarian hormones such as hormone replacement therapy. Reproductive factors resulting in increased lifetime exposure to endogenous ovarian hormones have also been linked to an increased risk of lobular breast cancer, and taken together, these data make a case for the role of ovarian hormones in the genesis and progression of the disease. In this review, we summarize current understanding of the epidemiological associations between ovarian hormones and lobular breast cancer and highlight mechanistic links that may underpin the etiology and biology.

Association of hormone receptors and human epidermal growth factor receptor-2/neu expressions with clinicopathologic factors of breast carcinoma: a cross-sectional study in a tertiary care hospital, Kabul, Afghanistan

BACKGROUND

Breast cancer (BC) is one of the major causes of death worldwide. It is the most common cause of death before the age of 70 years. The incidence and mortality of BC are rapidly increasing, posing great challenges to the health system and economy of every nation.

METHODOLOGY

A cross-sectional analytical study was conducted at the Department of Pathology and Clinical Laboratory of the French Medical Institute for Mothers and Children (FMIC) to demonstrate the association of human epidermal growth factor receptor 2 (Her2/Neu) and estrogen receptor (ER)/ progesterone receptor (PR) with clinical as well as pathological parameters among women with BC. A consecutive nonprobability sampling method was used for this study over a span of one and a half years.

RESULTS

One hundred twenty participants diagnosed with breast cancer were included in the study. The mean age at diagnosis was 44.58 ± 11.16 years. Out of the total patients, 68 (56.7%) were above 40 years old, 108 (90%) were married, 94 (78.3%) were multiparous, and 88 (73.3%) had a history of breastfeeding. 33.3% of cases were within the age range of menopause (40-50 years). The positive expression rates of ER, PR, and Her2/neu were found to be 48.8%, 44.6%, and 44.6%, respectively, and Her2/neu overexpression was found to be higher among ER/PR-negative cases.

CONCLUSION

In our study, we demonstrated that among Afghan women, grade II invasive ductal carcinoma, not otherwise specified, was the most common type of BC and frequently affected women above the age of 40. We also revealed that the percentage of negative ER (50.4%), negative PR (54.4%), and concordant ER/PR-negative cases were high compared to other possibilities. Additionally, the study revealed that expression of Her2/neu was in contrast with the expression of ER and PR receptors. The findings of our study still support the importance of performing immunohistochemical stains for hormonal receptor classification in terms of better clinical outcomes and prognosis.

[Association between reproductive history, breast cancer subtype, and survival in premenopausal women]

BACKGROUND AND OBJECTIVE

Reproductive history influences breast cancer risk. We analysed its association with tumour subtype and survival in premenopausal women.

PATIENTS AND METHODS

Retrospective, observational study of premenopausal women with stage I-III breast carcinoma in the last 20 years. Review of reproductive history, clinical data, and treatments in health records.

RESULTS

In 661 premenopausal women (32.40% of 1377 total cases), median age was 47 years (19-53), menarche 12 (7-17), first delivery 28 (16-41) and number of deliveries 2 (0-9). One hundred and eleven (18.20%) were nulliparous. Three hundred and fifty-nine (58.80%) used natural lactation, with a median duration of 6 months. Anovulatory drugs were used by 271 (44.40%), with a median duration of 36 months. Associations were found between menarche <10 years and lower risk of luminal subtype (OR: 0.52, 95% CI: 0.28-0.94; P=.03), between menarche >11 years and lower risk of HER2 subtype (OR: 0.50, 95% CI: 0.26-0.97; P=.04) and between first birth >30 years and lower risk of triple negative subtype (OR: 0.40, 95% CI: 0.17-0.93; P=.03). The 20-year overall and disease-free survival probabilities were 0.80 (95% CI: 0.71-0.90) and 0.72 (95% CI: 0.64-0.79) respectively. Patients with ≥1 delivery had better overall survival than nulliparous patients (HR: 0.51, 95% CI: 0.27-0.96, P=.04).

CONCLUSIONS

The findings suggest an association between age at menarche and age at first delivery and breast cancer subtype. Nulliparity is associated with worse survival.

What Is Known about Breast Cancer in Young Women?

Breast cancer (BC) is the second leading cause of cancer-related death in women under the age of 40 years worldwide. In addition, the incidence of breast cancer in young women (BCYW) has been rising. Young women are not the focus of screening programs and BC in younger women tends to be diagnosed in more advanced stages. Such patients have worse clinical outcomes and treatment complications compared to older patients. BCYW has been associated with distinct tumour biology that confers a worse prognosis, including poor tumour differentiation, increased Ki-67 expression, and more hormone-receptor negative tumours compared to women >50 years of age. Pathogenic variants in cancer predisposition genes such as BRCA1/2 are more common in early-onset BC compared to late-onset BC. Despite all these differences, BCYW remains poorly understood with a gap in research regarding the risk factors, diagnosis, prognosis, and treatment. Age-specific clinical characteristics or outcomes data for young women are lacking, and most of the standard treatments used in this subpopulation currently are derived from older patients. More age-specific clinical data and treatment options are required. In this review, we discuss the epidemiology, clinicopathologic characteristics, outcomes, treatments, and special considerations of breast cancer in young women. We also underline future directions and highlight areas that require more attention in future studies.

Adherence to a western dietary pattern and risk of invasive ductal and lobular breast carcinomas: a case-control study

Little is known about the role of diet in the risk of invasive ductal carcinoma (IDC) and invasive lobular carcinoma (ILC) of the breast, the most common histological subtypes of breast cancer (BC). This is because, the majority of studies on the association of diet and the risk of BC are focused on single food items, and studies considering the overall diet in terms of dietary patterns are limited. Also, the potential heterogeneity in the impact of Western diet (WD) on histological subtypes of BC is not established. This, the age-frequency-matched case–control study included 1009 incident BC cases and 1009 healthy controls. The required data was obtained from the patients’ medical files and interviews using a previously validated researcher-designed questionnaire for collecting data on socio-economic and anthropometric statuses and a valid food frequency questionnaire (FFQ) to measure the participants’ dietary intake. We used multinomial logistic regression, and odds ratios (ORs) with 95% confidence intervals (CIs) were calculated. A positive and significant association was observed between higher adherence to a WD and risk of IDC (OR comparing highest with the lowest tertile: 2.45, 95% CI 1.88, 3.17; p-trend < 0.001), whereas no significant association was observed between adherence to the WD and the risk of ILC (OR comparing highest with the lowest tertile: 1.63, 95% CI 0.63, 3.25) (p for heterogeneity = 0.03). The results of an analysis stratified by menopausal status suggested a similar pattern. We provided evidence that adherence to a WD raises the risk of IDC, but not ILC, suggesting different etiological mechanisms for IDC and ILC.

Multivariate analysis of independent roles of socioeconomic status, occupational physical activity, reproductive factors, and postmenopausal hormonal therapy in risk of breast cancer

PURPOSE

This case-control study assesses the independent roles of reproductive history, postmenopausal hormonal therapy (HT), socioeconomic status (SES), and occupational physical activity on the risk of breast cancer (BC).

METHODS

Odds ratios (OR) were estimated from conditional logistic multivariate regression model in a data set of 19,253 Finnish women diagnosed with BC between 1994 and 2013 and 96,265 age-matched population controls.

RESULTS

Both pre- and postmenopausal white-collar workers had significantly increased risk of ductal and lobular BC as compared to manual workers. Moderate occupational physical activity reduced risk of lobular BC by 14%. There was a transient increase in the risk of BC observed after each birth followed by a protective effect starting some years after the delivery. As the number of children increased, the short-term excess risk was lower and protective effect was observed earlier. Continuous estrogen-progestin therapy (EPT) significantly increased the risk of both ductal and lobular BC and the magnitude of risk was directly proportional to duration of use (OR for 5+ years of use 2.26, 95% confidence interval 2.12-2.42). Monthly EPT for 5+ years increased the risk (OR 1.32, 95% CI 1.20-1.45). Users of estradiol plus levonorgestrel intrauterine system devices showed ORs of 1.56 (95% CI 1.45-1.69) and 2.18 (95% CI 1.81-2.64) for ductal and lobular BC, respectively.

CONCLUSION

This study concludes that pregnancy has a dual effect on BC risk, with a transient increase in risk followed by a long-term protective effect. The SES and HT have a large effect on BC risk while occupational physical activity has only a small independent effect.

Breast Cancer-Epidemiology, Risk Factors, Classification, Prognostic Markers, and Current Treatment Strategies-An Updated Review

Simple Summary

Breast cancer is the most common cancer among women. It is estimated that 2.3 million new cases of BC are diagnosed globally each year. Based on mRNA gene expression levels, BC can be divided into molecular subtypes that provide insights into new treatment strategies and patient stratifications that impact the management of BC patients. This review addresses the overview on the BC epidemiology, risk factors, classification with an emphasis on molecular types, prognostic biomarkers, as well as possible treatment modalities.

Abstract

Breast cancer (BC) is the most frequently diagnosed cancer in women worldwide with more than 2 million new cases in 2020. Its incidence and death rates have increased over the last three decades due to the change in risk factor profiles, better cancer registration, and cancer detection. The number of risk factors of BC is significant and includes both the modifiable factors and non-modifiable factors. Currently, about 80% of patients with BC are individuals aged >50. Survival depends on both stage and molecular subtype. Invasive BCs comprise wide spectrum tumors that show a variation concerning their clinical presentation, behavior, and morphology. Based on mRNA gene expression levels, BC can be divided into molecular subtypes (Luminal A, Luminal B, HER2-enriched, and basal-like). The molecular subtypes provide insights into new treatment strategies and patient stratifications that impact the management of BC patients. The eighth edition of TNM classification outlines a new staging system for BC that, in addition to anatomical features, acknowledges biological factors. Treatment of breast cancer is complex and involves a combination of different modalities including surgery, radiotherapy, chemotherapy, hormonal therapy, or biological therapies delivered in diverse sequences.

Mediation analysis of racial disparities in triple-negative breast cancer incidence among postmenopausal women

BACKGROUND

Triple-negative breast cancer (TNBC) is disproportionately higher in Black women relative to White women. The objective of this study was to examine to what extent the association between race/ethnicity and risk of TNBC is mediated by potentially modifiable factors.

METHODS

A total of 128,623 Black and White women aged 50-79 years from the Women's Health Initiative were followed for a mean of 15.8 years. 643 incident TNBC cases (92 Black women and 551 White women) were confirmed by medical record review. Mediation analyses were conducted using an approach under a counterfactual framework.

RESULTS

Black women had approximately twofold higher risk of TNBC compared with white women (HR = 1.93, 95% CI 1.52-2.45). We observed that 48% of the racial disparity was mediated by metabolic dysfunction defined by having 3 or more cardiometabolic risk factors including elevated waist circumference, having history of diabetes, high cholesterol and hypertension. The racial disparity was not significantly mediated by other factors studied, including socioeconomic, lifestyle or reproductive factors.

CONCLUSION

Our study observed that approximately half of the racial disparity between postmenopausal Black and White women in TNBC incidence was driven by metabolic dysfunction.

Survival Outcomes in Invasive Lobular Carcinoma Compared to Oestrogen Receptor-Positive Invasive Ductal Carcinoma

Invasive lobular breast cancer (ILC) accounts for 10-15% of breast cancers and has distinct characteristics compared with the more common invasive ductal carcinoma (IDC). Studies have shown that ILC may be less sensitive to chemotherapy than IDC, with lower rates of complete pathological response after neo-adjuvant chemotherapy, but it is not clear how this affects long-term survival. Patients at Guy's and St Thomas' NHS Foundation Trust between 1975 and 2016 diagnosed with ER+ IDC or ER+ ILC were eligible for inclusion. Kaplan-Meier plots and Cox proportional-hazards regression models were used for analysis. There was no difference in overall survival comparing ER+ ILC to ER+ IDC (OR: 0.94, 95% CI: 0.83, 1.04) with a median follow-up time of 8.3 years compared to 8.4 years in IDC. However, ER+HER2- ILC had worse survival compared to ER+HER2- IDC in those that received chemotherapy (OR: 1.46, 95% CI: 1.06, 2.01). Here, median follow-up time was 7.0 years in ILC compared to 8.1 years in IDC. These results indicate worse overall survival after chemotherapy (neo-adjuvant and adjuvant) in ILC compared to ER+HER2- IDC even when correcting for tumour grade, age, size, and nodal involvement, but validation is needed in a larger study population.

A Review of Modifiable Risk Factors in Young Women for the Prevention of Breast Cancer

Breast cancer is the most common cancer diagnosis in women aged less than 40 years and the second most common cause of cancer death in this age group. Global rates of young onset breast cancer have risen steadily over the last twenty years. Although young women with breast cancer have a higher frequency of underlying pathogenic mutations in high penetrance breast cancer susceptibility genes (CSG) than older women, the vast majority of young breast cancer patients are not found to have a germline CSG mutation. There is therefore a need to inform young women regarding non-genetic breast cancer risk factors which have the potential to be influenced by changes in individual behaviour. A Pubmed search was performed using the search terms “young” or “early onset”, and “breast cancer” and “modifiable risk”. Titles and abstracts from peer-reviewed publications were screened for relevance. This review presents evidence for potentially modifiable risk factors of breast cancer risk in young women, including lifestyle factors (physical activity, body habitus, alcohol use, smoking, shift work and socioeconomic factors), reproductive and hormonal factors and iatrogenic risks. The extent to which these factors are truly modifiable is discussed and interactions between genetic and non-genetic risk factors are also addressed. Health care professionals have an opportunity to inform young women about breast health and risk when presenting at a “teachable moment”, including the benefits of physical activity and alcohol habits as risk factor. More focussed discussions regarding individual personal risk and benefit should accompany conversations regarding reproductive health and take into consideration both non-modifiable and iatrogenic BC risk factors.

Is There an Association between β-Carotene and Breast Cancer? A Systematic Review on Breast Cancer Risk

It is suspected that diet influences the risk of developing breast cancer. Several β-carotenoids have been inversely associated with breast cancer risk, but association by type of tumor and participant characteristics remain nuclear. The objective of this review of epidemiological studies is to investigate the relationship between β-carotenoids and breast cancer. This review covers the 2014-2020 period and was carried out using the PubMed and EMBASE databases. Only epidemiological studies carried out on β-carotenoids and breast cancer were included. The initial keyword search yielded 1559 results and finally a total of 28 studies were included. The quality of the articles and the risk of bias for each included article were assessed. The selected articles were subsequently classified according to their quality. The evidence from the included studies confirms that there is an association between β-carotenoids and breast cancer risk; the dietary intake of β-carotenoids may be beneficial in reducing the risk of developing breast cancer.

Key steps for effective breast cancer prevention

Despite decades of laboratory, epidemiological and clinical research, breast cancer incidence continues to rise. Breast cancer remains the leading cancer-related cause of disease burden for women, affecting one in 20 globally and as many as one in eight in high-income countries. Reducing breast cancer incidence will likely require both a population-based approach of reducing exposure to modifiable risk factors and a precision-prevention approach of identifying women at increased risk and targeting them for specific interventions, such as risk-reducing medication. We already have the capacity to estimate an individual woman's breast cancer risk using validated risk assessment models, and the accuracy of these models is likely to continue to improve over time, particularly with inclusion of newer risk factors, such as polygenic risk and mammographic density. Evidence-based risk-reducing medications are cheap, widely available and recommended by professional health bodies; however, widespread implementation of these has proven challenging. The barriers to uptake of, and adherence to, current medications will need to be considered as we deepen our understanding of breast cancer initiation and begin developing and testing novel preventives.

Parity reduces mammary repopulating activity but does not affect mammary stem cells defined as CD24 + CD29/CD49fhi in mice

BACKGROUND

Breast cancer (BCa) mortality is decreasing with early detection and improvement in therapies. The incidence of BCa, however, continues to increase, particularly estrogen-receptor-positive (ER +) subtypes. One of the greatest modifiers of ER + BCa risk is childbearing (parity), with BCa risk halved in young multiparous mothers. Despite convincing epidemiological data, the biology that underpins this protection remains unclear. Parity-induced protection has been postulated to be due to a decrease in mammary stem cells (MaSCs); however, reports to date have provided conflicting data.

METHODS

We have completed rigorous functional testing of repopulating activity in parous mice using unfractionated and MaSC (CD24^midCD49f^hi)-enriched populations. We also developed a novel serial transplant method to enable us to assess self-renewal of MaSC following pregnancy. Lastly, as each pregnancy confers additional BCa protection, we subjected mice to multiple rounds of pregnancy to assess whether additional pregnancies impact MaSC activity.

RESULTS

Here, we report that while repopulating activity in the mammary gland is reduced by parity in the unfractionated gland, it is not due to a loss in the classically defined MaSC (CD24⁺CD49f^hi) numbers or function. Self-renewal was unaffected by parity and additional rounds of pregnancy also did not lead to a decrease in MaSC activity.

CONCLUSIONS

Our data show instead that parity impacts on the stem-like activity of cells outside the MaSC population.

Heterogeneous Associations Between Obesity and Reproductive-Related Factors and Specific Breast Cancer Subtypes Among Hong Kong Chinese Women

Previous studies reported heterogeneous associations between obesity and reproductive-related breast cancer risk factors and breast cancer intrinsic subtypes; however, few studies have been conducted in Asian populations. Here, we aimed to examine whether risks associated with established breast cancer risk factors varied by breast cancer subtypes in Chinese women. We conducted a hospital-based case-control study in Hong Kong, including a total of 2169 Chinese women. Unconditional polytomous logistic regression models were used to calculate adjusted odds ratios (AORs) and 95% confidence intervals(95%CIs) to estimate relative risks associated with examined risk factors in case-control analyses and to test for heterogeneity across breast cancer subtypes in case-case analyses. In case-case analyses, compared with luminal A patients, luminal B (AOR = 1.76, 95% CI = 1.07-2.88), HER2 overexpressing (AOR = 3.40, 95% CI = 1.56-7.39), and triple negative (TNBC, AOR = 2.39, 95% CI = 1.18-4.82) patients were more likely to be postmenopausal. In case-control analyses, reduced risks associated with parity and younger age at first birth were only seen for luminal A and B cases especially among postmenopausal women, whereas having ≥ 3 children was associated with increased risk for HER2 overexpressing and TNBC among premenopausal women. Obesity was associated with increased risk for all subtypes. We found heterogeneous associations between parity-related risk factors by menopausal status and breast cancer subtypes among Chinese patients, which is similar to those observed in Western populations. Interestingly, obesity was associated with increased breast cancer risk regardless of menopausal status or subtypes, except for premenopausal luminal patients, which appears to be unique in Asian populations.

Heterogeneity in risk factors for ductal and lobular breast carcinomas: A case-control study

Invasive ductal carcinoma (IDC) and invasive lobular carcinoma (ILC) of the breast are the most common histological subtypes of breast cancer. However, the associations and heterogeneity between histological subtypes and their risk factors are not well established. This study aimed to investigate risk factors for IDC and ILC. This case-control study included 1,009 incident breast cancer cases and 1,009 hospital controls, frequency-matched by age. Data were obtained from the patients' medical files and an interview administered via a questionnaire. Multinomial logistic regression was used and odds ratios (ORs) and 95% confidence intervals (CIs) were calculated. The heterogeneity of the associations was assessed using the Wald test. Family history of breast cancer was associated with IDC (OR 2.64, 95% CI: 1.97-3.55) but not ILC (OR 0.81, 95% CI: 0.42-1.57; p for heterogeneity <0.001). Conversely, a history of miscarriage was associated with ILC (OR 1.71, 95% CI: 1.17-2.51) but not IDC (OR 1.18, 95% CI: 0.95-1.46; p for heterogeneity = 0.04). Similarly, type 2 diabetes was associated with ILC but not IDC (p for heterogeneity = 0.02). Age at first delivery and breastfeeding were significantly associated with IDC but not ILC, though p values for heterogeneity did not reach the significance level. Deliberate weight loss and age at menarche were significantly associated with ILC but not IDC (p for heterogeneity ≥0.27). Smoking, history of benign breast disease and BMI were associated with both subtypes. The present study supports the hypothesis that IDC and ILC are etiologically distinct tumours.

Risk Reduction of Breast Cancer by Childbirth, Breastfeeding, and Their Interaction in Korean Women: Heterogeneous Effects Across Menopausal Status, Hormone Receptor Status, and Pathological Subtypes

Objectives

The purpose of this study was to examine the associations of childbirth, breastfeeding, and their interaction with breast cancer (BC) risk reduction, and to evaluate the heterogeneity in the BC risk reduction effects of these factors by menopause, hormone receptor (HR) status, and pathological subtype.

Methods

BC patients aged 40+ from the Korean Breast Cancer Registry in 2004-2012 and controls from the Health Examinee cohort participants were included in this study after 1:1 matching (12 889 pairs) by age and enrollment year. BC risk according to childbirth, breastfeeding, and their interaction was calculated in logistic regression models using odds ratios (ORs) and 95% confidence intervals (CIs).

Results

BC risk decreased with childbirth (3+ childbirths relative to 1 childbirth: OR, 0.66; 95% CI, 0.56 to 0.78 and OR, 0.80; 95% CI, 0.68 to 0.95 in postmenopausal and premenopausal women, respectively); and the degree of risk reduction by the number of children was heterogeneous according to menopausal status (p-heterogeneity=0.04), HR status (p-heterogeneity<0.001), and pathological subtype (p-heterogeneity<0.001); whereas breastfeeding for 1-12 months showed a heterogeneous association with BC risk according to menopausal status, with risk reduction only in premenopausal women (p-heterogeneity<0.05). The combination of 2 more childbirths and breastfeeding for ≥13 months had a much stronger BC risk reduction of 49% (OR, 0.51; 95% CI, 0.45 to 0.58).

Conclusions

This study suggests that the combination of longer breastfeeding and more childbirths reduces BC risk more strongly, and that women who experience both 2 or more childbirths and breastfeed for ≥13 months can reduce their BC risk by about 50%.

Reproductive risk factor associations with lobular and ductal carcinoma in the Carolina Breast Cancer Study

BACKGROUND

Invasive lobular breast tumors display unique reproductive risk factor profiles. Lobular tumors are predominantly Luminal A subtype, and it is unclear whether reported risk factor associations are independent of molecular subtype.

METHODS

Polytomous logistic regression was used to estimate odds ratios (ORs) and 95% confidence intervals (95% CIs) for the associations between risk factors and histologic subtype [ductal (n = 2,856), lobular (n = 326), and mixed ductal-lobular (n = 473)] in the Carolina Breast Cancer Study (1993-2013). Three-marker immunohistochemical clinical subtypes were defined as Luminal A (ER+ or PR+/HER2-), Luminal B (ER+ or PR+/HER2+), Triple Negative (ER-/PR-/HER2-), and HER2+ (ER-/PR-/HER2+).

RESULTS

In case-case analyses compared to ductal, lobular tumors were significantly associated with lactation duration > 12 months [OR 1.86, 95% CI (1.33-2.60)], age at first birth ≥ 26 years [OR: 1.35, 95% CI: (1.03-1.78)], and current oral contraceptive use [OR: 1.86, 95% CI: (1.08-3.20)]. Differences in risk factor associations between ductal and lobular tumors persisted after restricting to Luminal A subtype.

CONCLUSIONS

Lobular tumors were associated with older age at first birth, increased lactation duration, and current oral contraceptive use. Etiologic heterogeneity by histology persisted after restricting to Luminal A subtype, suggesting both tumor histology and intrinsic subtype play integral parts in breast cancer risk.

Mammary stem cells and parity-induced breast cancer protection- new insights

Parity (childbearing) significantly decreases a woman's risk of breast cancer and the protective effect is greater if the woman is younger and has more children. The mechanism/s of parity-induced protection are not known. Although several factors are postulated to play a role, we discuss how a reduction in the number of mammary stem cells (MaSCs) may lead to a reduction in breast cancer risk in parous women. Firstly we review the epidemiology linking childbearing to reduced breast cancer risk and discuss how additional births, a young age at first full term birth, and breastfeeding impact the protection. We then detail the mouse and human studies implicating MaSC in parity induced protection and the in-vivo work being performed in mice to directly investigate the effect of parity on MaSC. Finally we discuss the transplant and lineage tracing experiments assessing MaSC activity according to parity and the need to define if MaSC are indeed more carcinogen sensitive than mature mammary epithelial cells. Continuing and future studies attempting to define the parity induced mechanisms will aid in the development of preventative therapies.

Estrogen Effects on the Mammary Gland in Early and Late Life and Breast Cancer Risk

A woman has an increased risk of breast cancer if her lifelong estrogen exposure is increased due to an early menarche, a late menopause, and/or an absence of childbearing. For decades, it was presumed that the number of years of exposure drove the increased risk, however, recent epidemiological data have shown that early life exposure (young menarche) has a more significant effect on cancer risk than late menopause. Thus, rather than the overall exposure it seems that the timing of hormone exposure plays a major role in defining breast cancer risk. In support of this, it is also known that aberrant hormonal exposure prior to puberty can also increase breast cancer risk, yet the elevated estrogen levels during pregnancy decrease breast cancer risk. This suggests that the effects of estrogen on the mammary gland/breast are age-dependent. In this review article, we will discuss the existing epidemiological data linking hormone exposure and estrogen receptor-positive breast cancer risk including menarche, menopause, parity, and aberrant environmental hormone exposure. We will discuss the predominantly rodent generated experimental data that confirm the association with hormone exposure and breast cancer risk, confirming its use as a model system. We will review the work that has been done attempting to define the direct effects of estrogen on the breast, which are beginning to reveal the mechanism of increased cancer risk. We will then conclude with our views on the most pertinent questions to be addressed experimentally in order to explore the relationship between age, estrogen exposure, and breast cancer risk.

Hair Coloring, Stress, and Smoking Increase the Risk of Breast Cancer: A Case-Control Study

PURPOSE

Epidemiologic characteristics of breast cancer in Iran are significantly different from those in the West and even other regional countries, but little is known about the related factors.

PATIENTS AND METHODS

A hospital-based case-control study was conducted on 1052 women (526 new cases and 526 controls). Logistic regression was performed to investigate associations of study factors with breast cancer risk.

RESULTS

This study introduced occupation (odds ratio [OR]_{employed/household}, 1.77; 95% confidence interval [CI], 1.15-2.69), marital age (OR_{24-30 y/< 18 y}, 2.13; 95% CI, 1.03-4.40), age at first delivery (OR_{≥ 30 y/< 18 y}, 3.53; 95% CI, 1.73-7.18), parity (OR_{1-2/Nulliparous or never married}, 2.61; 95% CI, 1.13-6.02), birth interval (OR_{30-50 mos/< 18 mos}, 2.38; 95% CI, 1.45-3.89), lifetime breastfeeding (OR_{≥ 42 mos/< 6 mos}, 0.37; 95% CI, 0.18-0.77), and menarche age (year) (OR, 0.87; 95% CI, 0.79-0.96) as significant associates of breast cancer. In addition, body mass index (OR, 1.07; 95% CI, 1.02-1.11) and some health-related behaviors including hair coloring on a regular basis (OR_yes/no, 1.93; 95% CI, 1.41-2.62), smoking (OR_yes/no, 2.02; 95% CI, 1.22-3.34), oral contraceptive usage (OR_ever/never. 1.46; 95% CI, 1.05-2.04), physical inactivity (OR_{inactive/regular activity}, 1.54; 95% CI, 1.39-1.75), past life stress (OR_{often stressful/often calm}, 2.40; 95% CI, 1.62-3.56), and regular bedtime (OR_{often regular/no}, 0.32; 95% CI, 0.19-0.54) were related to a higher risk of breast cancer.

CONCLUSION

This study revealed a significant number of factors that seem to contribute to the risk of breast cancer even more than the other previously introduced factors.

Breastfeeding Mode and Risk of Breast Cancer: A Dose-Response Meta-Analysis

BACKGROUND

Breastfeeding reduces women's risk of breast cancer. Since exclusive breastfeeding has a stronger hormonal effect, it could theoretically result in a greater reduction in breast cancer risk than any breastfeeding mode. No meta-analysis has examined breast cancer risk by breastfeeding mode. Research aim: The authors conducted a meta-analysis for breast cancer risk in parous women who breastfed exclusively or in any mode versus parous women who formula fed their infants, and they estimated the summary dose-response association by the accumulated duration of any breastfeeding mode.

METHODS

A systematic review of studies published between 2005 and 2015 analyzing breastfeeding and breast cancer risk in women was conducted in PubMed and EBSCOhost. A meta-analysis ( n = 65 studies) with fixed effects (or random effects, if heterogeneity existed) was carried out stratified by breastfeeding mode and menopausal and parity status. A summary dose-response association was estimated using the generalized least-squares method.

RESULTS

The summary relative risk (SRR) for breast cancer in parous women who breastfed exclusively was 0.72, 95% confidence interval (CI) [0.58, 0.90], versus parous women who had never breastfed. For parous women who breastfed in any mode, the SRR was lower in both premenopausal women (0.86, 95% CI [0.80, 0.93]) and postmenopausal women (0.89, 95% CI [0.83, 0.95]). There was no heterogeneity or publication bias. There is weak evidence of a difference between exclusive and any breastfeeding mode ( p = .08). The summary dose-response curve was nonlinear ( p < .001).

CONCLUSION

Exclusive breastfeeding among parous women reduces the risk of breast cancer compared with parous women who do not breastfeed exclusively.

Breastfeeding: a reproductive factor able to reduce the risk of luminal B breast cancer in premenopausal White women

In the medical literature, the role of breastfeeding and reproductive factors in the risk of breast carcinoma is still an open debate in premenopausal women. We highlight the role of breastfeeding and reproductive factors in luminal A and luminal B, the most frequent breast cancers. This case-control study analyzes a White premenopausal population of 286 breast cancer patients, divided into molecular subtypes, and 578 controls matched by age. Multivariate logistic regression models were used to assess the relationships of breastfeeding and other reproductive factors (age at menarche, parity, age at first pregnancy, number of children) with the risk of breast cancers. Among the variables examined, reproductive factors did not alter the risk of cancer, whereas breastfeeding up to 12 months was a significant protective factor against luminal B breast cancer (multivariate odds ratio: 0.22, 95% confidence interval: 0.09-0.59, P=0.002). In contrast, luminal A cases did not significantly correlate with breastfeeding or other reproductive factors. Breastfeeding up to 12 months is strongly protective against the more aggressive luminal B, but not against the less aggressive luminal A breast cancer in premenopausal White women.

Parity association with clinicopathological factors in invasive breast cancer: a retrospective analysis

The aim of this study was to determine the relationship between parity and age at diagnosis, primary tumor size, axillary lymph node (ALN) metastasis, histological grade, and subtype classification in patients with breast cancer. Data from 392 patients with invasive breast cancer were collected and divided into four groups: nulliparous (parity 0), parity 1, parity 2, and parity ≥3. The relationship between parity and age at diagnosis was assessed using post hoc Dunnett's T3 test, and tumor size, the number of ALN metastases, and histological grade were analyzed using Spearman's rho test. Breast cancer subtypes were analyzed using the chi-square (χ²) test. The results showed that the mean age at diagnosis increased with increased parity, and the mean age of patients with parity ≥3 was significantly greater than that of patients with parity 0, parity 1, and parity 2. The mean age at diagnosis of patients with parity 2 was greater than that of patients with parity 1. There was no significant difference in the mean age between patients with parity 0 and parity 1 or parity 0 and parity 2. Parity was negatively correlated with ALN metastasis. Parity was not correlated with tumor size or histological grade and the proportion of the four subtypes in breast cancer. So, increased parity deferred the onset of breast cancer and inhibited the metastasis of ALN, but did not affect tumor size, histological grade, or the proportion of subtypes. Increased parity was a protective factor against breast cancer.

Cancer mortality in former East and West Germany: a story of unification?

Background

Health and social conditions vary between West and East Germany.

Methods

We analyzed annual mortality data of all recorded deaths caused by lung, colorectal, breast and prostate cancer in Germany as they are published by the Federal Bureau of Statistics (FBS) encompassing the period 1980–2014 for former West Germany (WG) and 1990–2014 for former East Germany (EG). To compare East and West Germany we computed the ratio of the mortality rates in both parts (mortality rate ratio, MRR, <1 indicates a lower mortality in EG). Forecasting methods of time series analyses were applied (model selection based on the Box/Jenkins approach) to predict 5-year trends until 2019.

Results

Lung cancer: In women mortality rose in both regions (WG: +2.8%, 1991–2014, EG: +2.2%, 1990–2014). In men mortality in WG declined between −2.1% and −1.2%, and by −2.7% (1993–2009) in EG which was followed by a plateau. Colorectal cancer: A decline was found in both WG (−3.1%, 1993–2014) and EG women (−3.8%, 1993–2008 and −2.0%, 2008–2014). A decline in EG men since 1992 (−0.9%, 1992–1997 and −2.3%, 1997–2014) mirrors the development in WG (−2.6%, 1995–2014). Breast cancer: Constant mortality decline in WG after 1996. In EG a decline (−2.4%, 1992–2007) was followed by a plateau with an MRR <1 (1990–2014). Prostate cancer: In WG a decline (−3.4%) came to a hold after 2007, while there was a constant decline of 1.5% in EG. The forecast indicated that mortality of colorectal/lung cancer in men and breast cancer reaches a plateau in future years.

Conclusion

Courses of mortality were similar between East and West, while existing differences are likely to remain in the near future.

Electronic supplementary material

The online version of this article (doi:10.1186/s12885-017-3086-y) contains supplementary material, which is available to authorized users.

Regional Variation in Disparities in Breast Cancer Specific Mortality Due to Race/Ethnicity, Socioeconomic Status, and Urbanization

PURPOSE

Disparities in breast cancer mortality due to race/ethnicity, area socioeconomic status (SES), and urbanization have been documented. This study examined if disparities in the risk of breast cancer specific mortality due to race/ethnicity, SES, and urbanization varied within diverse regions of California.

METHODS

We identified 163,569 cases of first primary female invasive breast cancer from the California Cancer Registry diagnosed between January, 2000 and December, 2013. Cox regression was used to compute hazard ratios (HR) and 95 % confidence intervals for race/ethnicity, SES, and urbanization within eight regions of California.

RESULTS

Blacks had an increased risk of mortality in the San Francisco Bay Area (SFBA) (HR = 1.37; 1.22-1.55), Desert Sierra (HR = 1.27; 1.08-1.49), San Diego/Orange (HR = 1.43; 1.19-1.71), and Los Angeles (LA) (HR = 1.31; 1.20-1.44). Japanese (HR = 0.62; 0.47-0.81), Chinese (HR = 0.71; 0.58-0.87), and Filipino (HR = 0.81; 0.69-0.95) women had a decreased risk of mortality in LA. Southeast Asians had a decreased risk in San Diego/Orange (HR = 0.72; 0.57-0.90) and in the SFBA (HR = 0.81; 0.67-0.98). Hispanics had a decreased risk (HR = 0.73; 0.57-0.93) and American Indians had an increased risk (HR = 2.32; 1.08-4.98) in the Tri-County region. SES was a significant risk factor for mortality in all regions except the North and Tri-County. Urbanization was a statistically significant factor for mortality only in LA (HR = 1.32; 1.08-1.60).

CONCLUSIONS

Disparities in breast cancer mortality, due to race/ethnicity, SES, and urbanization vary by region which suggests that further research is warranted concerning the role of geographic regions and neighborhoods in cancer outcomes.

Cancer statistics for African Americans, 2016: Progress and opportunities in reducing racial disparities

In this article, the American Cancer Society provides the estimated number of new cancer cases and deaths for blacks in the United States and the most recent data on cancer incidence, mortality, survival, screening, and risk factors for cancer. Incidence data are from the National Cancer Institute, the Centers for Disease Control and Prevention, and the North American Association of Central Cancer Registries, and mortality data are from the National Center for Health Statistics. Approximately 189,910 new cases of cancer and 69,410 cancer deaths will occur among blacks in 2016. Although blacks continue to have higher cancer death rates than whites, the disparity has narrowed for all cancers combined in men and women and for lung and prostate cancers in men. In contrast, the racial gap in death rates has widened for breast cancer in women and remained level for colorectal cancer in men. The reduction in overall cancer death rates since the early 1990s translates to the avoidance of more than 300,000 deaths among blacks. In men, incidence rates from 2003 to 2012 decreased for all cancers combined (by 2.0% per year) as well as for the top 3 cancer sites (prostate, lung, and colorectal). In women, overall rates during the corresponding time period remained unchanged, reflecting increasing trends in breast cancer combined with decreasing trends in lung and colorectal cancer rates. Five-year relative survival is lower for blacks than whites for most cancers at each stage of diagnosis. The extent to which these disparities reflect unequal access to health care versus other factors remains an active area of research. Progress in reducing cancer death rates could be accelerated by ensuring equitable access to prevention, early detection, and high-quality treatment. CA Cancer J Clin 2016;66:290-308. © 2016 American Cancer Society.

Recreational physical activity and risk of triple negative breast cancer in the California Teachers Study

BACKGROUND

Evidence has accumulated showing that recreational physical activity reduces breast cancer risk. However, it is unclear whether risk reduction pertains to specific receptor-defined subtypes. Moreover, few studies have examined whether changes in the amount of recreational physical activity during adulthood influence breast cancer risk.

METHODS

A total of 108,907 women, ages 22 to 79 years with no history of breast cancer when joining the California Teachers Study in 1995-1996, completed a baseline questionnaire and were eligible for the study. Through 2012, 5882 women were diagnosed with invasive breast cancer. Breast cancer subtypes were defined by the expression status of estrogen receptor (ER), progesterone receptor (PR), and human epidermal growth factor receptor 2 (HER2). Multivariable Cox proportional hazards models provided adjusted hazard ratios (HRs) and 95 % confidence intervals (CIs) for breast cancer overall and ER/PR/HER2-defined subtypes associated with long-term (from high school through age 54 or age at cohort entry, whichever was younger) and baseline (during 3 years prior to baseline) recreational physical activity. Among women who also completed a follow-up questionnaire at 10 years after baseline in 2005-2008 (54,686 women, 1406 with invasive breast cancer), risk associated with changes in the amount of recreational physical activity from baseline to the 10-year follow-up (during 3 years prior to the 10-year follow-up) was determined.

RESULTS

Both long-term and baseline strenuous recreational physical activity were inversely associated with risk of invasive breast cancer (P trend ≤0.03). The observed associations were mainly confined to women with triple negative breast cancer (TNBC, ER-/PR-/HER2-, P trend ≤0.02) or luminal A-like subtype (ER+ or PR+ plus HER2-) who were former users of menopausal hormone therapy at baseline (P trend = 0.02, P homogeneity of trends ≤0.03). Moreover, women who consistently engaged in the highest level (≥3.51 h/wk/y) of strenuous recreational physical activity between baseline and 10-year follow-up had the lowest risk of breast cancer (HR = 0.71, 95 % CI = 0.52-0.98) when compared to those who were consistently low (≤0.50 h/wk/y).

CONCLUSIONS

Strenuous recreational physical activity is associated with lower breast cancer risk, especially TNBC. The benefit may be maximized by consistently engaging in high-intensity recreational physical activity during adulthood.

Reinterpretation of the results of a pooled analysis of dietary carotenoid intake and breast cancer risk by using the interval collapsing method

OBJECTIVES:

A pooled analysis of 18 prospective cohort studies reported in 2012 for evaluating carotenoid intakes and breast cancer risk defined by estrogen receptor (ER) and progesterone receptor (PR) statuses by using the “highest versus lowest intake” method (HLM). By applying the interval collapsing method (ICM) to maximize the use of the estimated information, we reevaluated the results of the previous analysis in order to reinterpret the inferences made.

METHODS:

In order to estimate the summary effect size (sES) and its 95% confidence interval (CI), meta-analyses with the random-effects model were conducted for adjusted relative risks and their 95% CI from the second to the fifth interval according to five kinds of carotenoids and ER/PR status.

RESULTS:

The following new findings were identified: α-Carotene and β-cryptoxanthin have protective effects on overall breast cancer. All five kinds of carotenoids showed protective effects on ER− breast cancer. β-Carotene level increased the risk of ER+ or ER+/PR+ breast cancer. α-Carotene, β-carotene, lutein/zeaxanthin, and lycopene showed a protective effect on ER−/PR+ or ER−/PR− breast cancer.

CONCLUSIONS:

The new facts support the hypothesis that carotenoids that show anticancer effects with anti-oxygen function might reduce the risk of ER− breast cancer. Based on the new facts, the modification of the effects of α-carotene, β-carotene, and β-cryptoxanthin should be evaluated according to PR and ER statuses.

Understanding rural-urban differences in risk factors for breast cancer in an Indian population

PURPOSE

Although cancer registry data indicate that there are large differences in breast cancer (BC) rates between rural and urban regions of India, the reasons for these differences are not well understood.

METHODS

We conducted a hospital based case-control study (1,637 breast cancer cases; 1,515 visitor controls) in Mumbai, India, during the years 2009-2013. Extensive questionnaire data, anthropometry measurement and blood samples were collected on all participants. Using logistic regression models, we estimated risk based on odds ratio (OR) and 95 % confidence intervals (CI) for various reproductive and anthropometric measures, stratified by rural-urban status depending upon residence in first 20 years of life.

RESULTS

Waist-to-hip ratio of ≥0.95 compared to ratio ≤0.84 was strongly associated with risk of BC in both rural and urban populations (ORurban = 4.10, 95 % CI 3.03-5.56; ORrural = 3.01, 95 % CI 1.85-4.90). First full-term pregnancy after the age of 25 compared to first full-term pregnancy below 20 years of age was associated with risk of BC in both urban and rural women (ORurban = 1.78, 95 % CI 1.32-2.41; ORrural = 2.24, 95 % CI 1.13-4.43). The prevalence of age at first full-term pregnancy was significantly lower in rural (mean age at first full-term pregnancy = 19.39 years) versus urban women (mean age at first full-term pregnancy = 22.62 years), whereas mean waist circumference was much higher in urban women (82.13 cm) compared to rural women (79.26 cm). We did not observe any association between breast feeding and risk of BC.

CONCLUSIONS

Differences in the prevalence of central adiposity and age at first full-term pregnancy between rural and urban women from India may explain some differences in breast cancer rates between these two populations.

TREC to WHERE? Transdisciplinary Research on Energetics and Cancer

When information is exchanged across disciplinary boundaries, resources are shared, and discipline-specific approaches are altered to achieve a common scientific goal, we create a new intellectual space for transdisciplinary research. This approach, fostered heavily by multiple NCI-funded initiatives, has the potential to forge new understanding of major public health issues. By breaking down disciplinary barriers, we work toward making real, meaningful, and lasting forward motion in addressing key public health issues. One of the transdisciplinary initiatives of the NCI is TREC: Transdisciplinary Research on Energetics and Cancer. In this article, we review the goals and scope of TREC, as well as the ways in which the initiative promotes transdisciplinary science. A particular focus is on multiple examples of the most unique aspect of the initiative: the funding of developmental projects across multiple TREC centers, toward the goal of incubating high-risk science that has the potential to translate into major leaps forward in understanding energetics in cancer. As we enter an era of greater focus on investigator-initiated science, new approaches may be needed to ensure that the peer review process is not solely organized along disciplinary lines. Inclusion of expertise regarding transdisciplinarity, as well as representation from multiple scientific disciplines within a panel, may allow transdisciplinary research to receive an educated hearing. The body of researchers trained to work in a transdisciplinary research space is ideally suited to address these challenges.

Breast cancer risk factor associations differ for pure versus invasive carcinoma with an in situ component in case-control and case-case analyses

PURPOSE

Invasive ductal carcinoma (IDC) is diagnosed with or without a ductal carcinoma in situ (DCIS) component. Previous analyses have found significant differences in tumor characteristics between pure IDC lacking DCIS and mixed IDC with DCIS. We will test our hypothesis that pure IDC represents a form of breast cancer with etiology and risk factors distinct from mixed IDC/DCIS.

METHODS

We compared reproductive risk factors for breast cancer risk, as well as family and smoking history between 831 women with mixed IDC/DCIS (n = 650) or pure IDC (n = 181), and 1,620 controls, in the context of the Women's Circle of Health Study (WCHS), a case-control study of breast cancer in African-American and European-American women. Data on reproductive and lifestyle factors were collected during interviews, and tumor characteristics were abstracted from pathology reports. Case-control and case-case analyses were conducted using unconditional logistic regression.

RESULTS

Most risk factors were similarly associated with pure IDC and mixed IDC/DCIS. However, among postmenopausal women, risk of pure IDC was lower in women with body mass index (BMI) 25 to <30 [odds ratio (OR) 0.66; 95 % confidence interval (CI) 0.35-1.23] and BMI ≥ 30 (OR 0.33; 95 % CI 0.18-0.67) compared to women with BMI < 25, with no associations with mixed IDC/DCIS. In case-case analyses, women who breastfed up to 12 months (OR 0.55; 95 % CI 0.32-0.94) or longer (OR 0.47; 95 % CI 0.26-0.87) showed decreased odds of pure IDC than mixed IDC/DCIS compared to those who did not breastfeed.

CONCLUSIONS

Associations with some breast cancer risk factors differed between mixed IDC/DCIS and pure IDC, potentially suggesting differential developmental pathways. These findings, if confirmed in a larger study, will provide a better understanding of the developmental patterns of breast cancer and the influence of modifiable risk factors, which in turn could lead to better preventive measures for pure IDC, which have worse disease prognosis compared to mixed IDC/DCIS.

Breastfeeding and breast cancer risk by receptor status--a systematic review and meta-analysis

BACKGROUND

Breastfeeding is inversely associated with overall risk of breast cancer. This association may differ in breast cancer subtypes defined by receptor status, as they may reflect different mechanisms of carcinogenesis. We conducted a systematic review and meta-analysis of case-control and prospective cohort studies to investigate the association between breastfeeding and breast cancer by estrogen receptor (ER), progesterone receptor (PR), and human epidermal growth factor receptor 2 (HER2) status.

DESIGN

We searched the PubMed and Scopus databases and bibliographies of pertinent articles to identify relevant articles and used random-effects models to calculate summary odds ratios (ORs) and 95% confidence intervals (CIs).

RESULTS

This meta-analysis represents 27 distinct studies (8 cohort and 19 case-control), with a total of 36 881 breast cancer cases. Among parous women, the risk estimates for the association between ever (versus never) breastfeeding and the breast cancers negative for both ER and PR were similar in three cohort and three case-control studies when results were adjusted for several factors, including the number of full-term pregnancies (combined OR 0.90; 95% CI 0.82-0.99), with little heterogeneity and no indication of publication bias. In a subset of three adjusted studies that included ER, PR, and HER2 status, ever breastfeeding showed a stronger inverse association with triple-negative breast cancer (OR 0.78; 95% CI 0.66-0.91) among parous women. Overall, cohort studies showed no significant association between breastfeeding and ER+/PR+ or ER+ and/or PR+ breast cancers, although one and two studies (out of four and seven studies, respectively) showed an inverse association.

CONCLUSIONS

This meta-analysis showed a protective effect of ever breastfeeding against hormone receptor-negative breast cancers, which are more common in younger women and generally have a poorer prognosis than other subtypes of breast cancer. The association between breastfeeding and receptor-positive breast cancers needs more investigation.

The Influence of Socioeconomic Status on Racial/Ethnic Disparities among the ER/PR/HER2 Breast Cancer Subtypes

Background. The eight ER/PR/HER2 breast cancer subtypes vary widely in demographic and clinicopathologic characteristics and survival. This study assesses the contribution of SES to the risk of mortality for blacks, Hispanics, Asian/Pacific Islanders, and American Indians when compared with white women for each ER/PR/HER2 subtype. Methods. We identified 143,184 cases of first primary female invasive breast cancer from the California Cancer Registry between 2000 and 2012. The risk of mortality was computed for each race/ethnicity within each ER/PR/HER2 subtype. Models were adjusted for tumor grade, year of diagnosis, and age. SES was added to a second set of models. Analyses were conducted separately for each stage. Results. Race/ethnicity did not contribute to the risk of mortality for any subtype in stage 1 when adjusted for SES. In stages 2, 3, and 4, race/ethnicity was associated with risk of mortality and adjustment for SES changed the risk only in some subtypes. SES reduced the risk of mortality by over 45% for American Indians with stage 2 ER+/PR+/HER2− cancer, but it decreased the risk of mortality for blacks with stage 2 triple negative cancer by less than 4%. Conclusions. Racial/ethnic disparities do not exist in all ER/PR/HER2 subtypes and, in general, SES modestly alters these disparities.

Breast cancer risk after full-term pregnancies among African women from Nigeria, Cameroon, and Uganda

BACKGROUND

The breast cancer (BC) risk profiles of African women differ significantly from those of women of European ancestry. African women are younger at the age of onset and tend to have high parity. The purpose of this study was to examine the relationship between full‐term pregnancy (FTP) and the risk of BC.

METHODS

A case‐control study was conducted among 1995 women with invasive BC and 2631 controls in Nigeria, Cameroon, and Uganda. Odds ratios (ORs) for individual ages at FTP according to the time since delivery were calculated and adjusted for confounders. A fitted spline model was used to assess the impact of the number of pregnancies on BC risk.

RESULTS

In comparison with a nulliparous woman, a parous woman with her first FTP at 20 years showed an OR of 0.76 (95% confidence interval [CI], 0.57‐0.99) for developing BC in the following 5 years. Ten years later, this risk was 0.76 (95% CI, 0.58‐0.99) and 0.76 (95% CI, 0.58‐0.98) for women aged 25 and 30 years, respectively. Similarly, a parous woman with 1 pregnancy had an OR of 0.69 (95% CI, 0.49‐0.96), whereas the OR was 0.66 (95% CI, 0.48‐0.91) with 2 or 5 pregnancies and 0.67 (95% CI, 0.47‐0.94) with 6 pregnancies in comparison with nulliparous women.

CONCLUSIONS

In contrast to studies in women of European ancestry, this study showed no transient increase in the risk of developing BC after FTP among African women. Further studies are needed to examine the impact of reproductive factors on early‐onset BC in African women. Cancer 2015;121:2237–2243. © 2015 American Cancer Society.

There is no transient increase in breast cancer risk after a full‐term pregnancy among African women. The protection conferred by pregnancy occurs immediately after the first full‐term pregnancy regardless of the age at that pregnancy and the number of pregnancies.

Lobular breast cancer: incidence and genetic and non-genetic risk factors

While most invasive breast cancers consist of carcinomas of the ductal type, about 10% are invasive lobular carcinomas. Invasive lobular and ductal carcinomas differ with respect to risk factors. Invasive lobular carcinoma is more strongly associated with exposure to female hormones, and therefore its incidence is more subject to variation. This is illustrated by US figures during the 1987 to 2004 period: after 12 years of increases, breast cancer incidence declined steadily from 1999 to 2004, reflecting among other causes the decreasing use of menopausal hormone therapy, and these variations were stronger for invasive lobular than for invasive ductal carcinoma. Similarly, invasive lobular carcinoma is more strongly associated with early menarche, late menopause and late age at first birth. As for genetic risk factors, four high-penetrance genes are tested in clinical practice when genetic susceptibility to breast cancer is suspected, BRCA1, BRCA2, TP53 and CDH1. Germline mutations in BRCA1 and TP53 are predominantly associated with invasive ductal carcinoma, while BRCA2 mutations are associated with both ductal and lobular cancers. CDH1, the gene coding for the E-cadherin adhesion protein, is of special interest as mutations are associated with invasive lobular carcinoma, but never with ductal carcinoma. It was initially known as the main susceptibility gene for gastric cancer of the diffuse type, but the excess of breast cancers of the lobular type in CDH1 families led researchers to identify it also as a susceptibility gene for invasive lobular carcinoma. The risk of invasive lobular carcinoma is high in female mutation carriers, as about 50% are expected to develop the disease. Carriers must therefore undergo intensive breast cancer screening, with, for example, yearly magnetic resonance imaging and mammogram starting at age 30 years.

Pregnancy-associated breast cancer in women from Shanghai: risk and prognosis

Breast cancer (BC) has been associated with pregnancy if diagnosed within 5-10 years after delivery (pregnancy-associated BC, PABC). PABC carries a poor prognosis compared to sporadic BC in Western populations. Data are limited regarding PABC in Asian populations, where longer periods of breastfeeding, higher birth rates and a lower median age of BC at diagnosis have been noted, all of which are known to influence prognosis. We used two datasets of women treated for early BC in Shanghai 1990-2012 (n = 10,161 and n = 7,411). For the analysis of BC risk after pregnancy we compared the distribution of pregnancy in our dataset to that in Shanghai using age-specific fertility rates. For disease-free survival (DFS) evaluation, we restricted our data to women ≤45 years. Women <30 years had a significantly elevated BC risk within 5 years of completing a pregnancy compared to women who had not been pregnant in the previous 5 years. In women aged 20-24 the relative risk (RR) was 3.33 (P = 0.012), and for women aged 25-29 the RR was 1.76 (P = 0.0074). For women >30, the RR was decreased. Patients with PABC had a higher risk of recurrence or death (hazard ratio (HR) for DFS 1.72, P = 0.019) compared to women with non-PABC by univariable analysis. Age was eliminated from the multivariable model by backward selection, resulting in tumor stage (3 versus 1, HR 3.08, P < .001) and recent pregnancy (HR 1.62, P < 0.05) as significant independent prognosticators. Having had a full-term pregnancy in the previous 5 years was associated with a 62 % increased risk of recurrence. We show that recent full-term pregnancy significantly elevates BC risk in women <30 in Shanghai, and that women diagnosed with PABC have a particularly adverse prognosis. Health care providers and women in Asian populations should be made aware of these results.

Temporal trends in the inflammatory cytokine profile of human breastmilk

A longer lifetime duration of breastfeeding may decrease the risk of breast cancer by reducing breast inflammation and mitigating inflammatory cytokine expression during postlactational involution. However, little is known about how the inflammatory cytokine profile in human breastmilk changes over time. To study temporal trends in breastmilk cytokine expression, we measured 80 human cytokines in the whey fraction of breastmilk samples from 15 mothers at 1, 4, 8, and 12 weeks postpartum. We used mixed models to identify temporal changes in cytokine expression and investigated parity status (multiparous vs. primiparous) as a potential confounder. Nine cytokines (monocyte chemoattractant protein-1, epithelial-derived neutrophil-activating protein-78, hepatocyte growth factor, insulin-like growth factor-binding protein-1, interleukin-16, interleukin-8, macrophage colony-stimulating factor, osteoprotegerin, and tissue inhibitor of metallopeptidase-2) had significantly decreased expression with increasing breastfeeding duration; all nine have known roles in breast involution, inflammation, and cancer and may serve as biomarkers of changing breast microenvironment. No cytokine significantly increased in level over the study period. Total protein concentration significantly decreased over time (p<0.0001), which may mediate the association between length of breastfeeding and inflammatory cytokine expression. Parity status did not confound temporal trends, but levels of several cytokines were significantly higher among multiparous versus primiparous women. Our results suggest that inflammatory cytokine expression during lactation is dynamic, and expressed milk may provide a noninvasive window into the extensive biological changes that occur in the postpartum breast.

Modern reproductive patterns associated with estrogen receptor positive but not negative breast cancer susceptibility

It has long been accepted that modern reproductive patterns are likely contributors to breast cancer susceptibility because of their influence on hormones such as estrogen and the importance of these hormones in breast cancer. We conducted a meta-analysis to assess whether this ‘evolutionary mismatch hypothesis’ can explain susceptibility to both estrogen receptor positive (ER-positive) and estrogen receptor negative (ER-negative) cancer. Our meta-analysis includes a total of 33 studies and examines parity, age of first birth and age of menarche broken down by estrogen receptor status. We found that modern reproductive patterns are more closely linked to ER-positive than ER-negative breast cancer. Thus, the evolutionary mismatch hypothesis for breast cancer can account for ER-positive breast cancer susceptibility but not ER-negative breast cancer.

Parity, lactation, and breast cancer subtypes in African American women: results from the AMBER Consortium

BACKGROUND

African American (AA) women have a disproportionately high incidence of estrogen receptor-negative (ER-) breast cancer, a subtype with a largely unexplained etiology. Because childbearing patterns also differ by race/ethnicity, with higher parity and a lower prevalence of lactation in AA women, we investigated the relation of parity and lactation to risk of specific breast cancer subtypes.

METHODS

Questionnaire data from two cohort and two case-control studies of breast cancer in AA women were combined and harmonized. Case patients were classified as ER+ (n = 2446), ER- (n = 1252), or triple negative (ER-, PR-, HER2-; n = 567) based on pathology data; there were 14180 control patients. Odds ratios (ORs) and 95% confidence intervals (CIs) were estimated in polytomous logistic regression analysis with adjustment for study, age, reproductive and other risk factors.

RESULTS

ORs for parity relative to nulliparity was 0.92 (95% CI = 0.81 to 1.03) for ER+, 1.33 (95% CI = 1.11 to 1.59) for ER-, and 1.37 (95% CI = 1.06 to 1.70) for triple-negative breast cancer. Lactation was associated with a reduced risk of ER- (OR = 0.81, 95% CI = 0.69 to 0.95) but not ER+ cancer. ER- cancer risk increased with each additional birth in women who had not breastfed, with an OR of 1.68 (95% CI = 1.15 to 2.44) for 4 or more births relative to one birth with lactation.

CONCLUSIONS

The findings suggest that parous women who have not breastfed are at increased risk of ER- and triple-negative breast cancer. Promotion of lactation may be an effective tool for reducing occurrence of the subtypes that contribute disproportionately to breast cancer mortality.

Epigenetic marks in estrogen receptor alpha CpG island correlate with some reproductive risk factors in breast cancer

Reproductive backgrounds, such as age at menarche and menopause, age of first full-term pregnancy (FFTP), number of full-term deliveries and oral contraceptive use are main hormone-related risk factors of breast cancer. It seems that the mentioned factors may affect the risk of breast cancer by enhancing the duration of exposure to estrogen as a potent carcinogen for breast tissue, but the molecular mechanism which links each risk factor to breast cancer is unclear. Estrogen mainly works via its nuclear receptor (ERα). As epigenetic alterations such as CpG methylation are potential links between endogenous or exogenous exposures and genome, we hypothesized that hormone-related risk factors may correlate with the epigenetic marks of the ERα promoter in breast tumors. In the present study, the CpG methylation status of the ERα gene in 99 samples of breast tumors belonged to women with different reproductive histories was evaluated. The reproductive history data were collected from patients. ERα CpG methylation was investigated by methylation specific PCR in DNA samples were obtained from the breast tumors. We could show that some of the hormone-related risk factors (early FFTP and increased number of pregnancies) were inversely correlated with epigenetic marks in ERα gene in breast tumors. Other hormone-related risk factors such as age of menarche and menopause and oral contraceptive use did not show any association with ERα methylation. It seems that pregnancy-related risk factors in comparison with other hormone-related factors work via different mechanism. As ERα methylation is a poor prognosis marker in breast tumors, its association with some modifiable reproductive risk factors (FFTP age and numbers of pregnancies) reiterates the importance of programming reproductive life style not only for prevention of breast cancer but also in favoring the prognosis of the affected women. The exact molecular mechanisms of the observed correlation need more investigation in the future.

Reproductive history and the risk of molecular breast cancer subtypes in a prospective study of Norwegian women

PURPOSE

Breast cancer can be classified into molecular subtypes that differ in clinical characteristics and prognosis. There is some but conflicting evidence that reproductive risk factors may differ between distinct breast cancer subtypes.

METHODS

We investigated associations of reproductive factors with the risk for six molecular breast cancer subtypes in a cohort of 21,532 Norwegian women who were born between 1886 and 1928 and followed up for breast cancer incidence between 1961 and 2008. We obtained stored tumor tissue from incident breast cancers and used immunohistochemistry and in situ hybridization to classify 825 invasive tumors into three luminal subtypes [Luminal A, Luminal B (HER2-) and Luminal B (HER2+)] and three non-luminal subtypes [human epidermal growth factor receptor 2 (HER2) subtype, basal-like phenotype (BP) and five negative phenotype (5NP)]. We used Cox regression to assess reproductive factors and risk for each subtype.

RESULTS

We found that young age at menarche, old age at first birth and low parity were associated with increased risk for luminal breast cancer subtypes. For the HER2 subtype, we either found no association or associations in the opposite direction compared to the luminal subtypes. The BP subtype appeared to have a similar reproductive risk profile as the luminal subtypes. Breastfeeding was associated with a reduced risk for HER2 and 5NP subtypes, but was not associated with any other subtype.

CONCLUSIONS

The results suggest that molecular breast cancer subtypes differ in their reproductive risk factors, but associations with non-luminal subtypes are still poorly understood and warrant further study.

Breastfeeding in relation to risk of different breast cancer characteristics

BACKGROUND

The aim of this present study was to examine duration of breastfeeding in relation to the risk of different subgroups of breast cancer. A prospective cohort, The Malmö Diet and Cancer study, including 14092 parous women, were followed during a mean of 10.2 years and a total of 424 incident breast cancers were diagnosed.

METHODS

Tumours were classified regarding invasiveness, tumour size, axillary lymph node status, Nottingham grade, tumour proliferation (Ki67), HER2, cyclin D1 and p27, WHO histological type and hormone receptor status. Duration of breastfeeding was measured using total time of breastfeeding, categorized in quartiles using the lowest as the reference group (<4.0, ≥4.0- < 8.0, ≥8.0- < 13.0 and ≥13.0 months). Average duration of breastfeeding per child and breastfeeding duration of the first child were also used as exposures in separate analyses. Relative risks, with 95% confidence intervals, were obtained using a Cox's proportional hazards analysis adjusted for potential confounders.

RESULTS

Overall risk for breast cancer was similar in all quartiles of breastfeeding. No strong results regarding breastfeeding duration and breast cancer subgroups were seen. A few results indicated an association between a relatively long duration of breastfeeding and tumours with high proliferation (Ki67) and grade III histological grade.

CONCLUSIONS

Breastfeeding duration was not associated with breast cancer risk and no strong results were seen with regard to breast cancer subgroups.

Cigarette smoking and postmenopausal breast cancer risk in a prospective cohort

Background:

The relationship between cigarette smoking and breast cancer risk has been inconsistent, potentially due to modification by other factors or confounding.

Methods:

We examined smoking and breast cancer risk in a prospective cohort of 186 150 female AARP (formerly American Association of Retired Persons) members, ages 50–71 years, who joined the study in 1995–96 by responding to a questionnaire. Through 2006, 7481 breast cancers were diagnosed. Multivariable-adjusted hazard ratios (HRs) were estimated, overall and stratified by breast cancer risk factors, using Cox proportional hazards regression. Multiplicative interactions were evaluated using the likelihood ratio test.

Results:

Increased breast cancer risk was associated with current (HR 1.19, 95% confidence interval (CI) 1.10–1.28) and former (HR 1.07, CI 1.01–1.13) smoking. The current smoking association was stronger among women without (HR 1.24, CI 1.15–1.35) as compared to those with a family history of breast cancer (HR 0.94, CI 0.78–1.13) (P-interaction=0.03). The current smoking association was also stronger among those with later (⩾15 years: HR 1.52, CI 1.20–1.94) as compared with earlier (⩽12 years: HR 1.14, CI 1.03–1.27; 13–14 years: HR 1.18, CI 1.05–1.32) ages at menarche (P-interaction=0.03).

Conclusions:

Risk was elevated in smokers, particularly in those without a family history or late menarche. Research into smoking's effects on the genome and breast development may clarify these relationships.

Reproductive risk factors and oestrogen/progesterone receptor-negative breast cancer in the Breast Cancer Family Registry

BACKGROUND

Oestrogen receptor (ER)- and progesterone receptor (PR)-negative (ER-PR-) breast cancer is associated with poorer prognosis compared with other breast cancer subtypes. High parity has been associated with an increased risk of ER-PR- cancer, but emerging evidence suggests that breastfeeding may reduce this risk. Whether this potential breastfeeding benefit extends to women at high risk of breast cancer remains critical to understand for prevention.

METHODS

Using population-based ascertained cases (n=4011) and controls (2997) from the Breast Cancer Family Registry, we examined reproductive risk factors in relation to ER and PR status.

RESULTS

High parity (≥3 live births) without breastfeeding was positively associated only with ER-PR- tumours (odds ratio (OR)=1.57, 95% confidence interval (CI), 1.10-2.24); there was no association with parity in women who breastfed (OR=0.93, 95% CI 0.71-1.22). Across all race/ethnicities, associations for ER-PR- cancer were higher among women who did not breastfeed than among women who did. Oral contraceptive (OC) use before 1975 was associated with an increased risk of ER-PR- cancer only (OR=1.32, 95% CI 1.04-1.67). For women who began OC use in 1975 or later there was no increased risk.

CONCLUSIONS

Our findings support that there are modifiable factors for ER-PR- breast cancer and that breastfeeding in particular may mitigate the increased risk of ER-PR- cancers seen from multiparity.

Specific carotenoid intake is inversely associated with the risk of breast cancer among Chinese women

The protective effect of dietary carotenoid intake on the risk of breast cancer is inconclusive. Moreover, data on dietary carotenoids in relation to breast cancer in non-Western populations are scarce. The aim of the present study was to examine the association between dietary carotenoid intake and the risk of breast cancer among Chinese women. A total of 561 cases and 561 controls who were frequency matched by age (5-year interval) and residence were recruited in the present case-control study. Dietary intake information was collected by a face-to-face interview using a validated FFQ. The OR and 95 % CI were assessed by multivariate logistic regression after adjusting for various potential confounders. An inverse association was observed between the consumption of α-carotene, β-carotene, β-cryptoxanthin and lutein/zeaxanthin and the risk of breast cancer. The multivariate-adjusted OR for the highest quartile of intake compared with the lowest quartile of intake were 0·61 (95 % CI 0·43, 0·88) for α-carotene, 0·54 (95 % CI 0·38, 0·78) for β-carotene, 0·38 (95 % CI 0·26, 0·52) for β-cryptoxanthin and 0·49 (95 % CI 0·34, 0·71) for lutein/zeaxanthin. Lycopene intake was not found to be associated with the risk of breast cancer, with the adjusted OR of 0·89 (95 % CI 0·61, 1·30). These inverse associations were more evident among pre-menopausal women and women who were exposed to second-hand smoke. The protective effect of specific carotenoid intake was observed for all subtypes of hormone receptor status of breast cancer. The present study indicated that a greater intake of specific carotenoids was associated with a decreased risk of breast cancer among Chinese women residing in Guangdong.