Age at menarche, age at menopause, height and obesity as risk factors for breast cancer: associations and interactions in an international case-control study

Replication of genetic loci for ages at menarche and menopause in the multi-ethnic Population Architecture using Genomics and Epidemiology (PAGE) study

STUDY QUESTION

Do genetic associations identified in genome-wide association studies (GWAS) of age at menarche (AM) and age at natural menopause (ANM) replicate in women of diverse race/ancestry from the Population Architecture using Genomics and Epidemiology (PAGE) Study?

SUMMARY ANSWER

We replicated GWAS reproductive trait single nucleotide polymorphisms (SNPs) in our European descent population and found that many SNPs were also associated with AM and ANM in populations of diverse ancestry.

WHAT IS KNOWN ALREADY

Menarche and menopause mark the reproductive lifespan in women and are important risk factors for chronic diseases including obesity, cardiovascular disease and cancer. Both events are believed to be influenced by environmental and genetic factors, and vary in populations differing by genetic ancestry and geography. Most genetic variants associated with these traits have been identified in GWAS of European-descent populations.

STUDY DESIGN, SIZE, DURATION

A total of 42 251 women of diverse ancestry from PAGE were included in cross-sectional analyses of AM and ANM.

MATERIALS, SETTING, METHODS

SNPs previously associated with ANM (n = 5 SNPs) and AM (n = 3 SNPs) in GWAS were genotyped in American Indians, African Americans, Asians, European Americans, Hispanics and Native Hawaiians. To test SNP associations with ANM or AM, we used linear regression models stratified by race/ethnicity and PAGE sub-study. Results were then combined in race-specific fixed effect meta-analyses for each outcome. For replication and generalization analyses, significance was defined at P < 0.01 for ANM analyses and P < 0.017 for AM analyses.

MAIN RESULTS AND THE ROLE OF CHANCE

We replicated findings for AM SNPs in the LIN28B locus and an intergenic region on 9q31 in European Americans. The LIN28B SNPs (rs314277 and rs314280) were also significantly associated with AM in Asians, but not in other race/ethnicity groups. Linkage disequilibrium (LD) patterns at this locus varied widely among the ancestral groups. With the exception of an intergenic SNP at 13q34, all ANM SNPs replicated in European Americans. Three were significantly associated with ANM in other race/ethnicity populations: rs2153157 (6p24.2/SYCP2L), rs365132 (5q35/UIMC1) and rs16991615 (20p12.3/MCM8). While rs1172822 (19q13/BRSK1) was not significant in the populations of non-European descent, effect sizes showed similar trends.

LIMITATIONS, REASONS FOR CAUTION

Lack of association for the GWAS SNPs in the non-European American groups may be due to differences in locus LD patterns between these groups and the European-descent populations included in the GWAS discovery studies; and in some cases, lower power may also contribute to non-significant findings.

WIDER IMPLICATIONS OF THE FINDINGS

The discovery of genetic variants associated with the reproductive traits provides an important opportunity to elucidate the biological mechanisms involved with normal variation and disorders of menarche and menopause. In this study we replicated most, but not all reported SNPs in European descent populations and examined the epidemiologic architecture of these early reported variants, describing their generalizability and effect size across differing ancestral populations. Such data will be increasingly important for prioritizing GWAS SNPs for follow-up in fine-mapping and resequencing studies, as well as in translational research.

The effect of gender and age on kidney cancer survival: younger age is an independent prognostic factor in women with renal cell carcinoma

OBJECTIVE

Gender-specific differences in incidence of renal cell carcinoma (RCC) and its outcome have previously been reported. We used age as a surrogate to test whether this might be hormone-related in a large international RCC cohort.

METHODS AND MATERIALS

This study included patients treated by nephrectomy at 10 international academic centers. Clinicopathologic features were assessed using chi-square and the Student t-tests. Kaplan-Meier survival estimates and Cox proportional hazards models addressed the effect of gender and age on disease-specific survival.

RESULTS

Of the 5,654 patients, 3,777 (67%) were men and 1,877 (33%) were women. Generally, women presented at lower T stages (P<0.001), had fewer metastases (P<0.001), and had lower-grade tumors (P<0.001). Women more frequently had clear-cell (87% vs. 82%) and less frequently had papillary RCC (7% vs. 12%) than men (P<0.001). Women had a 19% reduced risk of death from RCC than men (hazard ratio 0.81, 95% confidence interval 0.73-0.90, P<0.001). The survival advantage for women was present to the greatest degree in the age group<42 years (P = 0.0136) and in women aged 42 to 58 years (P<0.001), but was not apparent in patients aged 59 years and older (P = 0.248). Age was an independent predictor of disease-specific survival in women (hazard ratio 1.011, 95% confidence interval 1.004-1.019, P = 0.004), but not in men.

CONCLUSIONS

As a group, women present with less advanced tumors, leading to a 19% reduced risk of RCC-specific death compared with men. This survival difference is present only in patients aged<59 years. Because this gender-based survival difference is not related to pathologic features, the role of hormonal effects on the development and progression of RCC needs to be investigated.

Genetic variation and reproductive timing: African American women from the Population Architecture using Genomics and Epidemiology (PAGE) Study

Age at menarche (AM) and age at natural menopause (ANM) define the boundaries of the reproductive lifespan in women. Their timing is associated with various diseases, including cancer and cardiovascular disease. Genome-wide association studies have identified several genetic variants associated with either AM or ANM in populations of largely European or Asian descent women. The extent to which these associations generalize to diverse populations remains unknown. Therefore, we sought to replicate previously reported AM and ANM findings and to identify novel AM and ANM variants using the Metabochip (n = 161,098 SNPs) in 4,159 and 1,860 African American women, respectively, in the Women's Health Initiative (WHI) and Atherosclerosis Risk in Communities (ARIC) studies, as part of the Population Architecture using Genomics and Epidemiology (PAGE) Study. We replicated or generalized one previously identified variant for AM, rs1361108/CENPW, and two variants for ANM, rs897798/BRSK1 and rs769450/APOE, to our African American cohort. Overall, generalization of the majority of previously-identified variants for AM and ANM, including LIN28B and MCM8, was not observed in this African American sample. We identified three novel loci associated with ANM that reached significance after multiple testing correction (LDLR rs189596789, p = 5×10⁻⁰⁸; KCNQ1 rs79972789, p = 1.9×10⁻⁰⁷; COL4A3BP rs181686584, p = 2.9×10⁻⁰⁷). Our most significant AM association was upstream of RSF1, a gene implicated in ovarian and breast cancers (rs11604207, p = 1.6×10⁻⁰⁶). While most associations were identified in either AM or ANM, we did identify genes suggestively associated with both: PHACTR1 and ARHGAP42. The lack of generalization coupled with the potentially novel associations identified here emphasize the need for additional genetic discovery efforts for AM and ANM in diverse populations.

That recognised risk factors can explain past and present international differences in breast cancer incidence: misconceptions 5

Recent discussions on research priorities in the United States have revealed a widespread assumption that known risk factors entirely explain the historic international differences in rates of breast cancer. In fact, formal investigations of this question, both by modelling between-country differences and studies of migrants, indicate that an appreciable amount of the international differences in this disease remains unexplained. If this is not recognised, opportunities for research on breast cancer aetiology may be lost.

Evolutionary foundations for cancer biology

New applications of evolutionary biology are transforming our understanding of cancer. The articles in this special issue provide many specific examples, such as microorganisms inducing cancers, the significance of within-tumor heterogeneity, and the possibility that lower dose chemotherapy may sometimes promote longer survival. Underlying these specific advances is a large-scale transformation, as cancer research incorporates evolutionary methods into its toolkit, and asks new evolutionary questions about why we are vulnerable to cancer. Evolution explains why cancer exists at all, how neoplasms grow, why cancer is remarkably rare, and why it occurs despite powerful cancer suppression mechanisms. Cancer exists because of somatic selection; mutations in somatic cells result in some dividing faster than others, in some cases generating neoplasms. Neoplasms grow, or do not, in complex cellular ecosystems. Cancer is relatively rare because of natural selection; our genomes were derived disproportionally from individuals with effective mechanisms for suppressing cancer. Cancer occurs nonetheless for the same six evolutionary reasons that explain why we remain vulnerable to other diseases. These four principles-cancers evolve by somatic selection, neoplasms grow in complex ecosystems, natural selection has shaped powerful cancer defenses, and the limitations of those defenses have evolutionary explanations-provide a foundation for understanding, preventing, and treating cancer.

CYP2W1, CYP4F11 and CYP8A1 polymorphisms and interaction of CYP2W1 genotypes with risk factors in Mexican women with breast cancer

Breast cancer (BCa) is the leading type of cancer in Mexican women. Genetic factors, such as single nucleotide polymorphisms (SNP) of P450 system, have been reported in BCa. In this report, and for the first time in the literature, we analyzed the rs3735684 (7021 G>A), rs11553651 (15016 G>T) and rs56195291 (60020 C>G) polymorphisms in the CYP2W1, 4F11 and 8A1 genes in patients with BCa and in healthy Mexican women to identify a potential association between these polymorphisms and BCa risk. Patients and controls were used for polymorphism analysis using an allelic discrimination assay with TaqMan probes and confirmed by DNA sequencing. Links with clinic-pathological characteristics were also analyzed. Statistical analysis was performed using the standard χ2 or Fisher exact test statistic. No significant differences were observed in the distributions of CYP2W1 (OR 8.6, 95%CI 0.43-172.5 P>0.05; OR 2.0, 95%CI 0.76-5.4, P>0.05) and CYP4F11 (OR 0.3, 95%CI 0.01-8.4 P>0.05) genotypes between the patients and controls. Only the CYP8A1 CC genotype was detected in patients with BCa and the controls. All polymorphism frequencies were in Hardy-Weinberg Equilibrium (HWE) in the controls (P>0.05). We found a significant association between BCa risk and smoking, use of oral contraceptives or hormonal replacement therapy (HRT), obesity, hyperglycemia, chronic diseases, family history of cancer and menopausal status in the population studied (P<0.05). Tobacco, oral contraceptive or HRT, chronic diseases and obesity or overweight were strongly associated with almost eight, thirty-five, nine and five-fold increased risk for BCa. Tobaco, obesity and hyperglycemia significantly increased the risk of BCa in the patients carrying variant genotypes of CYP2W1 (P<0.05). These results indicate that the CYP2W1 rs3735684, CYP4F11 rs11553651 and CYP8A1 rs56195291 SNPs are not a key risk factor for BCa in Mexican women. This study did not detect an association between the CYP2W1, 4F11 and 8A1 genes polymorphisms and BCa risk in a Mexican population. However, some clinico-pathological risk factors interact with CYP2W1 genotypes and modifies susceptibility to BCa.

Relationship between body mass index and early menarche of adolescent girls in Seoul

OBJECTIVES

The object of this study was to determine the relationship between body mass index (BMI) and early menarche in adolescent girls in Seoul.

METHODS

A retrospective study was conducted with 144 middle school students in Seoul who provided informed consent. We measured their body composition, and used the questionnaire survey method for data collection from November to December 2008. Past elemental body composition data were collected from elementary school health records of first year of middle school.

RESULTS

The early menarcheal group was taller and heavier than the late menarcheal group (p<0.05 from 8-12 years old). The body fat percentage (%), BMI were higher in the early menarcheal girls than the late-menarcheal girls (p<0.05, age at 13). In the result of multiple logistic regression, the BMI at the age of 8 and 9 was associated with early menarche after adjusting for birth weight, breast feeding and age at menarche of the mother (BMI at the age of 8: p for trend=0.01, BMI at the age of 9: p for trend=0.04). An increase in BMI from 7 to 8 year was associated with early menarche after adjusting for birth weight, breast feeding, age at menarche of the mother (p for trend=0.048).

CONCLUSIONS

The BMI at the age of 8 and 9 was associated with the early menarche of girls and increase in BMI from 7 to 8 year was associated with the early menarche of girls. These results suggest that BMI and increase in BMI before menarche cause early menarche. Although this study does not represent all Korean adolescent girls, it is one of the few studies that have investigated the temporal relationship between BMI and early menarche.

Reproductive cancer risk factors among Alaska Native women: the Alaska Education and Research Towards Health (EARTH) Study

BACKGROUND

The purpose of this study was to provide estimates for the prevalence of reproductive cancer risk factors among Alaska Native (AN) women who enrolled in the Alaska Education and Research Towards Health (EARTH) Study from 2004 to 2006.

METHODS

A total of 2,315 AN women 18 years or older completed reproductive health questions as part of a comprehensive health history questionnaire. The reproductive health section included menstrual status (age at menarche and menopause), pregnancy and live birth history, use of hormonal contraception, hormone replacement therapy, and history of hysterectomy and/or oophorectomy.

RESULTS

A total of 463 (20%) of women experienced menarche before age 12 with a decline in mean age at menarche by age cohort. More than 86% had been pregnant (mean number of pregnancies, 3.8; mean number of live births, 2.9). More than one half of women (58%) had their first live birth between the ages of 18 and 24. Almost 28% of participants had completed menopause, of whom 24% completed menopause after age 52. Fewer than half (43%) reported ever using hormone replacement therapy. Almost two thirds (62%) reported ever using oral contraceptives, and fewer reported ever using birth control shots (30%) or implants (10%).

CONCLUSIONS

This study is unique in reporting reproductive health factors among a large group of AN women. These data show that AN women have selective protective factors for reproductive cancers, including low nulliparity rates, low use of menopausal estrogens, and common use of contraceptive hormones. However, analysis by age cohorts indicates decreasing age at menarche that might increase the risk for reproductive cancers among AN women in the future.

Correlation of the risk of breast cancer and disruption of the circadian rhythm (Review)

Breast cancer is the worldwide leading cause of cancer incidence among women. Night shift work exposure has been recently considered one of the significant breast cancer risk factors in industrialized countries. The mechanisms by which this work exposure may be responsible for cancer development is still discussed. In the last 15 years, many authors have paid attention to the relationship between night shift work and breast cancer risk. In the current study, eight case-control studies and four prospective epidemiological studies describing such relationship are discussed. A positive correlation between night shift work and breast cancer risk was described in 8 out of 12 studies. However, different reasons suggest that some of these studies have an Achilles heel according to the International Agency of Cancer (IARC) indications. Both the circadian system alteration and the melatonin output reduction, related to the exposure to light-at-night during night shift work, remain the most valid hypotheses on the causal relation of shift work and breast cancer. Overall, the results of the present study suggest that there is an association between night shift work and breast cancer development in western countries. However, further studies are needed to confirm such association and to understand which biomolecular mechanisms may be involved in the pathogenesis of cancer diagnosed in patients with night shift work exposure.

In vitro fertilization and breast cancer: is there cause for concern?

OBJECTIVE

To examine the incidence rate of breast cancer in a cohort of women undergoing treatment for infertility, comparing the rate in women who had in vitro fertilization (IVF) with those who did not.

DESIGN

Population-based cohort study using linked hospital and registry data.

SETTING

Hospital.

PATIENT(S)

All women aged 20-44 years seeking hospital investigation and treatment for infertility in Western Australia during the period 1983-2002 (n = 21,025).

INTERVENTION(S)

None.

MAIN OUTCOME MEASURE(S)

Hazard ratios (HRs) for breast cancer.

RESULT(S)

There was no overall increase in the rate of breast cancer in women who had IVF (HR 1.10, 95% confidence interval [CI] 0.88-1.36), but there was an increased rate in women who commenced IVF at a young age. Women who commenced hospital infertility treatment at 24 years and required IVF had an unadjusted HR of breast cancer of 1.59 (95% CI 1.05-2.42) compared with women of the same age who had infertility treatment but no IVF. When adjusted for late age at first delivery, which is associated with an increased rate of breast cancer, and delivery of twins and higher-order multiples, which is associated with a decreased rate of breast cancer, the HR remained elevated at 1.56 (95% CI 1.01-2.40). Hazard ratios were not elevated in women who commenced treatment at age 40 and required IVF (adjusted HR 0.87, 95% CI 0.62-1.22).

CONCLUSION(S)

Commencing IVF treatment at a young age is associated with an increased rate of breast cancer.

Study of leptin levels and gene polymorphisms in patients with central precocious puberty

INTRODUCTION

Three single-nucleotide polymorphisms (SNPs) in the leptin (LEP) or leptin receptor (LEPR) genes were assessed for their association with central precocious puberty (CPP).

RESULTS

The control group with the A/G SNP at LEPR 223 or A/G SNP at LEPR 109 exhibited significantly higher peak luteinizing hormone (LH) levels. The leptin level in the CPP group was significantly higher than that in the control group, but SNPs in either LEP or LEPR gene could not explain this observation.

DISCUSSION

In conclusion, SNPs at LEPR 223 and LEPR 109 were significantly associated with higher levels of LH in girls without CPP, but none of the genotypes at these SNPs were significantly associated with CPP.

METHODS

The SNP genotypes of LEP (polymorphism at promoter at nt-2548) and LEPR (223A/G, 109A/G) of 219 healthy girls and 249 girls diagnosed with CPP were compared. Allele frequencies in SNPs were compared with anthropometric measures, circulating leptin, hormones (estradiol, follicle-stimulating hormone, and LH), and lipid concentrations for CPP risk.

Reproductive aging-associated common genetic variants and the risk of breast cancer

Introduction

A younger age at menarche and an older age at menopause are well established risk factors for breast cancer. Recent genome-wide association studies have identified several novel genetic loci associated with these two traits. However, the association between these loci and breast cancer risk is unknown.

Methods

In this study, we investigated 19 and 17 newly identified single nucleotide polymorphisms (SNPs) from the ReproGen Consortium that have been associated with age at menarche and age at natural menopause, respectively, and assessed their associations with breast cancer risk in 6 population-based studies among up to 3,683 breast cancer cases and 34,174 controls in white women of European ancestry. In addition, we used these SNPs to calculate genetic risk scores (GRSs) based on their associations with each trait.

Results

After adjusting for age and potential population stratification, two age at menarche associated SNPs (rs1079866 and rs7821178) and one age at natural menopause associated SNP (rs2517388) were associated with breast cancer risk (p values, 0.003, 0.009 and 0.023, respectively). The odds ratios for breast cancer corresponding to per-risk-allele were 1.14 (95% CI, 1.05 to 1.24), 1.08 (95% CI, 1.02 to 1.15) and 1.10 (95% CI, 1.01 to 1.20), respectively, and were in the direction predicted by their associations with age at menarche or age at natural menopause. These associations did not appear to be attenuated by further controlling for self-reported age at menarche, age at natural menopause, or known breast cancer susceptibility loci. Although we did not observe a statistically significant association between any GRS for reproductive aging and breast cancer risk, the 4^th and 5^th highest quintiles of the younger age at menarche GRS had odds ratios of 1.14 (95% CI, 1.01 to 1.28) and 1.13 (95% CI, 1.00 to 1.27), respectively, compared to the lowest quintile.

Conclusions

Our study suggests that three genetic variants, independent of their associations with age at menarche or age at natural menopause, were associated with breast cancer risk and may contribute modestly to breast cancer risk prediction; however, the combination of the 19 age at menarche or the 17 age at natural menopause associated SNPs did not appear to be useful for identifying a high risk subgroup for breast cancer.

Influence of diabetes mellitus type 2 and prolonged estrogen exposure on risk of breast cancer among women in Armenia

Diabetes mellitus type 2 (DM2) and breast cancer (BrCa) are prevalent in Armenia. We investigated DM2, reproductive factors, and BrCa in a case control study of 302 women. Multiple logistic regression analyses revealed DM2 increased adjusted odds of BrCa by 5.53 (95% CI 1.34-22.81). Any birth was protective (adjusted OR=0.36, 95% CI 0.20-0.66). Each year delay in first pregnancy increased risk (adjusted OR=1.13, 95% CI 1.01-1.27) as did induced abortions (adjusted OR=2.86, 95% CI 1.02-8.04). Odds ratios were adjusted for age and body mass index (BMI), which confounded associations between DM2 and BrCa. We suggest our findings imply the need for further investigation in Armenian and in other populations with similar characteristics.

The importance of blood-borne viruses in elevated cancer risk among opioid-dependent people: a population-based cohort study

OBJECTIVE

To quantify cancer risk in opioid dependence and the association with infection by the oncogenic blood-borne viruses (BBVs) hepatitis C (HCV), hepatitis B (HBV) and HIV.

DESIGN

Cohort study.

SETTING

New South Wales, Australia.

PARTICIPANTS

All 45 412 adults aged 16 years or over registered for opioid substitution therapy (OST) between 1985 and 2007. Notifications of cancer, death and infection with HCV, HBV and HIV were ascertained by record linkage with registries.

MAIN OUTCOME MEASURES

The ratios of observed to expected number of cancers, standardised incidence ratios (SIRs), and the average annual per cent change (AAPC) in overall age and sex-standardised cancer incidence.

RESULTS

Overall cancer risk was modestly increased compared to the general population (SIR 1.15, 95% CI 1.07 to 1.23). Excess risk was observed for 11 cancers, particularly lung (4.02, 95% CI 3.32 to 4.82), non-Hodgkin's lymphoma (1.51, 95% CI 1.20 to 1.88) and liver (8.04, 95% CI 6.18 to 10.3). Reduced risk was observed for six cancers, including prostate (0.16, 95% CI 0.06 to 0.32) and breast (0.48, 95% CI 0.35 to 0.62). Individuals notified with HCV or HBV had a markedly increased risk of liver cancer; lung cancer risk was also increased in those with HCV. HIV was associated with an elevated risk of liver, anus and kidney cancer, non-Hodgkin lymphoma and Kaposi sarcoma. Cancer risk was not increased in individuals without a BBV notification, apart from pancreatic cancer (3.92, 95% CI 1.07 to 10.0). Cancer incidence increased significantly over time (AAPC 9.4%, 4.2% to 15%, p=0.001).

CONCLUSIONS

BBVs play a major role in the cancer risk profile of opioid-dependent individuals registered for OST. To address the dramatic increasing trend in cancer incidence, the OST setting could be utilised for cancer prevention strategies.

Association analyses suggest the effects of RANK and RANKL on age at menarche in Chinese women

OBJECTIVES

Age at menarche (AAM), the time of the first menstrual bleeding, is an important developmental milestone in the female life. It marks the beginning of the reproductive period. AAM is implicated in the risk of many health complications in later life. In this study, we conducted an analysis for association of single nucleotide polymorphisms (SNPs) and common haplotypes of two candidate genes, RANK (receptor activator of the NF-κB) and RANKL (receptor activator of the NF-κB ligand), with AAM in 825 unrelated Chinese women.

METHODS

In total, 73 SNPs of RANKL and 23 SNPs of RANK were genotyped. The SNPs and common haplotypes were then analyzed for their association with AAM. Age and age( 2 ) were used as covariates.

RESULTS

We found five individual SNPs (rs7239261, rs8094884, rs3826620, rs8089829, and rs9956850) of RANK significantly associated with AAM (p < 0.05). Although no significant association was identified for the RANKL gene, three polymorphisms showed nearly significant (0.05 < p < 0.08) association with AAM. Seven haplotypes of RANK were significantly associated with AAM (p < 0.05); the most significant association of the AT haplotype composed by rs1805034 and rs4524034 (p = 9.4 × 10(-4)) remained significant (p = 0.0235) after the Bonferroni correction for multiple testing. Three haplotypes of RANKL were significantly associated with AAM (p < 0.05). Importantly, the association of rs3826620 replicated our previous findings for Caucasian females.

CONCLUSIONS

The results of the present study suggest that the RANK and RANKL are two candidate genes for AAM in Chinese women.

Vitamin D deficiency and age at menarche: a prospective study

BACKGROUND

Early menarche is a risk factor for cardiometabolic disease and cancer. Latitude, which influences sun exposure, is inversely related to age at menarche. This association might be related to vitamin D, but to our knowledge it has not been investigated in prospective epidemiologic studies.

OBJECTIVE

We studied the association between vitamin D status and the occurrence of menarche in a prospective study in girls from Bogota, Colombia.

DESIGN

We measured plasma 25-hydroxyvitamin D [25(OH)D] concentrations in a random sample of 242 girls (mean ± SD age: 8.8 ± 1.6 y) and followed them for a median of 30 mo. Girls were asked periodically about the occurrence and date of menarche. Baseline 25(OH)D concentrations were categorized as <50 nmol/L (deficient), ≥50 and <75 nmol/L, or ≥75 nmol/L (sufficient). The incidence of menarche was compared between groups by using time-to-event analyses.

RESULTS

A total of 57% of girls in the vitamin D-deficient group reached menarche during follow-up compared with 23% of girls in the vitamin D-sufficient group (P-trend = 0.0004). The estimated mean (±SE) ages at menarche in the same groups were 11.8 ± 0.2 y and 12.6 ± 0.2 y, respectively (P = 0.0009). After adjustment for baseline age and BMI-for-age z score in a Cox proportional hazards model, the probability of menarche was twice as high in vitamin D-deficient girls than in girls who were vitamin D-sufficient (HR: 2.05; 95% CI: 1.03, 4.07; P = 0.04). Similar results were obtained in girls aged ≥9 y at baseline (HR: 2.39; 95% CI: 1.14, 5.00; P = 0.02).

CONCLUSION

Vitamin D deficiency is associated with earlier menarche.

Childhood factors associated with mammographic density in adult women

Growth and development factors could contribute to the development of breast cancer associated with an increase in mammographic density. This study examines the influence of certain childhood-related, socio-demographic and anthropometric variables on mammographic density in adult woman. The study covered 3574 women aged 45-68 years, participating in breast cancer-screening programmes in seven Spanish cities. Based on a craniocaudal mammogram, blind, anonymous measurement of mammographic density was made by a single radiologist, using Boyd's semiquantitative scale. Data associated with the early stages of life were obtained from a direct survey. Ordinal logistic regression and generalised linear models were employed to estimate the association between mammographic density and the variables covered by the questionnaire. Screening programme was introduced as a random effects term. Age, number of children, body mass index (BMI) and other childhood-related variables were used as adjustment variables, and stratified by menopausal status. A total of 811 women (23%) presented mammographic density of over 50%, and 5% of densities exceeded 75%. Our results show a greater prevalence of high mammographic density in women with low prepubertal weight (OR: 1.18; 95% CI: 1.02-1.36); marked prepubertal height (OR: 1.25; 95% CI: 0.97-1.60) and advanced age of their mothers at their birth (>39 years: OR: 1.28; 95% CI: 1.03-1.60); and a lower prevalence of high mammographic density in women with higher prepubertal weight, low birth weight and earlier menarche. The influence of these early-life factors may be explained by greater exposure to hormones and growth factors during the development of the breast gland, when breast tissue would be particularly susceptible to proliferative and carcinogenic stimulus.

Gestational weight gain and daughter's age at menarche

BACKGROUND

Sexual development begins in utero and enters a dormant phase during infancy. The influence of maternal gestational weight gain (GWG) on daughter's age at menarche has not been explored.

METHODS

We investigated the association between maternal GWG and age at menarche (<11 years, 11-15 years, >15 years of age) in a large cohort study of U.S. nurses, The Nurses' Health Study II (NHS II), and the Nurses' Mothers' Cohort Study.

RESULTS

Among 32,218 respondents, 7% reported age at menarche <l1, 90% aged 11-15 years, and 3% > age 15. Compared with women whose mothers gained 20-29 lbs during pregnancy, those whose mothers reported <10 lbs or >40 lbs of GWG were 30% more likely to report early onset menarche (<11 years of age) in logistic regression models adjusted for sociodemographic and maternal characteristics, and childhood body size and physical activity: adjusted odds ratio (OR) 1.31, 95% confidence interval (CI) 1.05-1.62, and 1.27, 95% CI 1.06-1.56. Maternal GWG was not associated with late menarche in the fully adjusted model (p(trend)=0.07).

CONCLUSIONS

These results suggest that either extreme of maternal GWG may influence risk for early age at menarche in daughters. Maternal GWG may be a modifiable risk factor for early menarche.

A meta-analysis of fat intake, reproduction, and breast cancer risk: an evolutionary perspective

OBJECTIVES

This study is a systematic review of literature published up to May of 2010 aimed to identify relationships between dietary fat, and fat subtypes, with risk of breast cancer in women.

METHODS

Descriptive data, estimates of relative risk and associated 95% confidence interval (CI) were extracted from relative studies and analyzed using the random effects model of DerSimonian and Laird.

RESULTS

Cohort study results indicated significant summary relative risks between polyunsaturated fat and breast cancer (1.091, 95% CI: 1.001; 1.184). In case-control studies no association between fat and breast cancer was observed. Post-menopausal women indicated a significant association between total fat (1.042, 95%CI: 1.013; 1.073), PUFA intake (1.22, 95% CI: 1.08; 1.381), and breast cancer. A non-significant inverse relation between intake of all fat types and breast cancer was identified in premenopausal women.

CONCLUSIONS

These results support the idea that possible elevations in serum estrogen levels by an adult exposure to a high-fat diet would increase breast cancer risk. Furthermore, menopausal status was observed to affect women's risk of breast cancer. Higher risks of breast cancer were found in post-menopausal women consuming diets high in total fat and polyunsaturated fats. Conversely, dietary fat appears to have preventative effects in pre-menopausal women. This study takes a transformative approach combining epidemiological, biomedical, and evolutionary theory to evaluate how biocultural variations in risk factors (i.e., diet and reproduction) affect the evolution of breast cancers.

Overweight, obesity, diabetes, and risk of breast cancer: interlocking pieces of the puzzle

We considered epidemiological data on overweight, diabetes, insulin, and breast cancer. Overweight is inversely related to premenopausal breast cancer, but there is definite evidence that, as compared with normal weight women, the relative risk (RR) for postmenopausal breast cancer is around 1.5 for overweight women and >2 for obese women, and that the association is stronger in elderly women. Overweight and obesity are strongly related to diabetes. Diabetes is associated with postmenopausal breast cancer, too, with summary RRs from meta-analyses of 1.15-1.20, but not with premenopausal breast cancer (RR, 0.9). There is no consistent evidence that fasting insulin is related to breast cancer risk. Thus, although overweight and obesity are strongly related to postmenopausal breast cancer, diabetes is only moderately related to it. Given the extent of the association, and the likely residual confounding by overweight, inference on causality for the diabetes-breast cancer relation remains open to discussion.

Familial concordance for age at menarche: analyses from the Breakthrough Generations Study

Age at menarche is correlated within families, but estimates of the heritability of menarcheal age have a wide range (0.45-0.95). We examined the familial resemblance for age at menarche and the extent to which this is due to genetic and shared environmental factors. Between 2003 and 2010 data were retrospectively collected by questionnaire from participants within the UK-based Breakthrough Generations Study. These analyses included 25,970 female participants aged 16-98 with at least one female relative who was also a study participant. A woman's menarche was significantly delayed for each yearly increase in the menarcheal age of her monozygotic twin (average increase = 7.2 months, P < 0.001), dizygotic twin (average increase = 3.0 months, P = 0.03), older sister (average increase = 3.3 months, P < 0.001), mother (average increase = 3.4 months, P < 0.001), maternal grandmother (average increase = 1.5 months, P = 0.04), maternal aunt (average increase = 1.4 months, P < 0.001) and paternal aunt (average increase = 3.0 months, P < 0.001). There was not a significant association between the menarcheal ages of half-sister pairs or of paternal grandmother-granddaughter pairs, based on small numbers. Heritability was estimated as 0.57 [95% confidence interval 0.53, 0.61]. Shared environmental factors did not have an effect in the model. In conclusion, approximately half of the variation in age at menarche was attributable to additive genetic effects with the remainder attributable to non-shared environmental effects.

Reported early family environment covaries with menarcheal age as a function of polymorphic variation in estrogen receptor-α

Age at menarche, a sentinel index of pubertal maturation, was examined in relation to early family relationships (conflict, cohesion) and polymorphic variation in the gene encoding estrogen receptor-α (ESR1) in a midlife sample of 455 European American women. Consistent with prior literature, women who reported being raised in families characterized by close interpersonal relationships and little conflict tended to reach menarche at a later age than participants reared in families lacking cohesion and prone to discord. Moreover, this association was moderated by ESR1 variation, such that quality of the family environment covaried positively with menarcheal age among participants homozygous for minor alleles of the two ESR1 polymorphisms studied here (rs9304799, rs2234693), but not among women of other ESR1 genotypes. In addition, (a) family relationship variables were unrelated to ESR1 variation, and (b) genotype-dependent effects of childhood environment on age at menarche could not be accounted for by personality traits elsewhere shown to explain heritable variation in reported family conflict and cohesion. These findings are consistent with theories of differential susceptibility to environmental influence, as well as the more specific hypothesis (by Belsky) that girls differ genetically in their sensitivity to rearing effects on pubertal maturation.

Role of prenatal characteristics and early growth on pubertal attainment of British girls

OBJECTIVES

The objective of this study was to explore the influence of maternal prenatal characteristics and behaviors and of weight and BMI gain during early childhood on the timing of various puberty outcomes in girls who were enrolled in the Avon Longitudinal Study of Parents and Children.

METHODS

Repeated self-assessments of pubertal development were obtained from approximately 4000 girls between the ages of 8 and 14. Data on prenatal characteristics and weight at birth and 2, 9, and 20 months of age were obtained from questionnaires, birth records, and clinic visits. Infants' weights were converted to weight-for-age and BMI SD scores (SDSs; z scores), and change values were obtained for the 0- to 20-month and other intervals within that age range. We used parametric survival models to estimate associations with age of entry into Tanner stages of breast and pubic hair and menarche.

RESULTS

Maternal initiation of menarche at age<12, smoking during pregnancy, and primiparity were associated with earlier puberty. A 1-unit increase in the weight SDS change values for the 0- to 20-month age interval was associated with earlier ages of entry into pubertal outcomes (0.19-0.31 years). Increases in the BMI SDS change values were also associated with earlier entry into pubertal outcomes (0.07-0.11 years).

CONCLUSIONS

Many of the maternal prenatal characteristics and weight and BMI gain during infancy seemed to have similar influences across different puberty outcomes. Either such early factors have comparable influences on each of the hormonal processes involved in puberty, or processes are linked and awakening of 1 aspect triggers the others.

TNFRSF11A and TNFSF11 are associated with age at menarche and natural menopause in white women

OBJECTIVE

Menarche and menopause mark the lower and upper limits of the female reproductive period. The timing of these events influences women's health in later life. The onsets of menarche and menopause have a strong genetic basis. We tested two genes, TNFRSF11A (RANK) and TNFSF11 (RANKL), for their association with age at menarche (AM) and age at natural menopause (ANM).

METHODS

Nineteen single nucleotide polymorphisms (SNPs) of TNFRSF11A and 12 SNPs of TNFSF11 were genotyped in a random sample of 306 unrelated white women. This sample was analyzed for the association of the SNPs and common haplotypes with AM. Then, a subsample of 211 women with natural menopause was analyzed for the association of both genes with ANM. Smoking, alcohol intake, and duration of lactation were applied as covariates in the association analyses.

RESULTS

Three polymorphisms of TNFSF11 were associated with AM: rs2200287 (P = 0.005), rs9525641 (P = 0.039), and rs1054016 (P = 0.047). Two SNPs of this gene, rs346578 and rs9525641, showed an association with ANM (P = 0.007 and P = 0.011, respectively). Two SNPs of TNFRSF11A were associated with AM (rs3826620; P = 0.022) and ANM (rs8086340; P = 0.015). Multiple SNP-SNP and SNP-environment interaction effects on AM and ANM were detected for both genes. One polymorphism of TNFRSF11A, rs4436867, was not directly associated with either trait but indicated significant interactions with four TNFSF11 polymorphisms on ANM. Two other TNFRSF11A polymorphisms, rs4941125 and rs7235803, showed interaction effects with several TNFSF11 polymorphisms on AM. Both genes manifested significant interaction with the duration of breast-feeding in their effect on ANM.

CONCLUSIONS

The TNFRSF11A and TNFSF11 genes are associated with the onset of AM and ANM in white women.

Prevention of breast cancer (part I): epidemiology, risk factors, and risk assessment tools

Advances in breast cancer research have led to declining death rates from this disease because of early detection through mammographic screening and improved therapy for breast cancer. The concept that breast cancer, in some cases, can be prevented has been explored over the last three decades. This article, part I of a two-part series, will focus on the epidemiology, the risk factors associated with breast cancer, and the available risk assessment tools, which can help define who should be considered for risk reduction strategies. Part II will focus on discussing risk reduction strategies.

Salivary progesterone levels before menarche: a prospective study of adolescent girls

OBJECTIVE

Our objective was to determine the frequency of ovulatory salivary progesterone levels before menarche in healthy girls.

DESIGN

We recruited a prospective cohort of midpubertal, premenarcheal girls. Participants collected weekly saliva samples until first menses or for 12 months. Menstrual cycles were considered to have ovulatory salivary progesterone levels if values were greater than 0.100 ng/ml (0.318 nmol/liter) 0-14 d before menarche.

SETTINGS

Participants collected saliva samples weekly at home and attended monthly clinic visits.

PATIENTS

Patients included 63 premenarcheal females, age 9-15 yr, with body mass index higher than the fifth percentile for age and Tanner stage III or greater for both pubic hair and breast development.

MAIN OUTCOME MEASURES

Frequency of ovulatory levels of salivary progesterone before menarche was assessed.

RESULTS

Fifty-five girls completed the study, and 43 experienced menarche. Of the 42 girls who reached menarche and provided a sample within 14 d of menarche, five (12%) had ovulatory progesterone levels. The mean anovulatory salivary progesterone level was 0.041 ng/ml (0.130 nmol/liter; range, 0.012-0.078 ng/ml, 0.038-0.248 nmol/liter), and the mean ovulatory level was 0.194 ng/ml (0.617 nmol/liter; range, 0.125-0.343 ng/ml, 0.398-1.09 nmol/liter). The levels of estrogen, testosterone, and 17-hydroxyprogesterone were higher and the mean BMI was lower in those with ovulatory progesterone levels vs. those with anovulatory levels.

CONCLUSION

A significant proportion of girls displayed ovulatory levels of progesterone before menarche. More research is needed to clarify the hormonal events that occur in the perimenarcheal time period.

Measuring indices of lifelong estrogen exposure: self-report reliability

OBJECTIVE

The utility of clinical markers of lifelong estrogen exposure is established in the understanding of breast cancer, osteoporosis and dementia, among others. However, a good number of studies rely on self-reports to ascertain the involvement of certain estrogen exposure indices. The goal of this study is to assess the reliability of self-reported lifelong estrogen exposure indices by measuring correlation between two repeats.

METHODS

A questionnaire assessing lifelong indices of estrogen exposure was developed (revised version included) and completed by 36 healthy postmenopausal women twice within a 4-year interval (age range from 50 to 79 years). Reliability was tested using Pearson's correlation coefficient.

RESULTS

Strong significant correlations were observed for most estrogen exposure indices and an effect of age was revealed. Age at menopause and age at initiation of hormone therapy were the two variables leading to weaker correlations across time of measurements; no relation was found between Time 1 and Time 2 when looking at the group of older women (over 65 years of age).

CONCLUSIONS

Overall, these results support the use of self-reported measures for most of the lifelong estrogen exposure indices, but they also warn us about the pitfalls of the climacteric period. However, the design of the current study did not allow us to test accuracy; thus, the validity of these self-reported variables needs to be addressed in the future.

A life course approach to reproductive health: theory and methods

Taking a life course approach to the study of reproductive health involves the investigation of factors across life and, also across generations, that influence the timing of menarche, fertility, pregnancy outcomes, gynaecological disorders, and age at menopause. It also recognises the important influence of reproductive health on chronic disease risk in later life. Published literature supports the use of an integrated life course approach to study reproductive health, which examines the whole life course, considers the continuity of reproductive health and the interrelationship between the different markers of this. This is in contrast to more traditional approaches that tend to focus only on contemporary risk factors and which consider each marker of reproductive health separately. For instance, we found evidence linking early life factors such as growth, socioeconomic conditions, and parental divorce with ages at menarche and menopause, although the nature of the relationship differs. We discuss the different theoretical models that are used within life course epidemiology and which postulate pathways linking exposures across the life course to health outcomes, using examples of relevance to the study of reproductive health. These highlight the importance of examining timing of exposures, such as during critical periods in early life, and the temporal order of exposures. How life course frameworks of reproductive health can be developed to help identify hypotheses to be tested is also demonstrated. This approach has implications for the development of effective health policy that moves beyond identifying not only the type of intervention but also the most appropriate time across life to intervene.

Association analyses suggest multiple interaction effects of the methylenetetrahydrofolate reductase polymorphisms on timing of menarche and natural menopause in white women

OBJECTIVE

This study aimed to investigate whether polymorphisms of the methylenetetrahydrofolate reductase (MTHFR) gene are associated with age at menarche and age at natural menopause in white women.

METHODS

In a cross-sectional study, a total of 305 randomly selected unrelated white women were genotyped for six single nucleotide polymorphisms (SNPs) of the MTHFR gene (including one common replacement, rs1801133). This sample was comprehensively analyzed for the association of the SNPs with age at menarche. Then a subsample of 210 women who experienced natural menopause was analyzed for the association of the MTHFR gene with age at natural menopause.

RESULTS

Duration of breast-feeding was a significant predictor of earlier natural menopause (P < 0.05). No individual SNPs were associated with either age at menarche or age at natural menopause. However, three significant (P < 0.05) SNP-SNP interaction effects (rs2066470/rs1476413, rs2066470/rs4846049, and rs17037390/rs4846049) on the onset of menarche were determined. Three haplotypes were significantly associated with age at menopause (P < 0.05). Four SNPs (rs2066470, rs17037390, rs1801133, and rs4846048) indicated significant interaction effects with various lifestyle factors on age at natural menopause.

CONCLUSIONS

The results of our study suggest that the MTHFR gene may influence the onset of menarche and natural menopause. This effect is probably due to the multiple SNP-SNP and SNP-environment interactions. More independent studies are needed to further clarify the possible contribution of this gene to the timing of menarche and menopause.

The breast cancer and the environment research centers: transdisciplinary research on the role of the environment in breast cancer etiology

OBJECTIVES

We introduce and describe the Breast Cancer and the Environment Research Centers (BCERC), a research network with a transdisciplinary approach to elucidating the role of environmental factors in pubertal development as a window on breast cancer etiology. We describe the organization of four national centers integrated into the BCERC network.

DATA SOURCES

Investigators use a common conceptual framework based on multiple levels of biologic, behavioral, and social organization across the life span. The approach connects basic biologic studies with rodent models and tissue culture systems, a coordinated multicenter epidemiologic cohort study of prepubertal girls, and the integration of community members of breast cancer advocates as key members of the research team to comprise the network.

DATA EXTRACTION

Relevant literature is reviewed that describes current knowledge across levels of organization. Individual research questions and hypotheses in BCERC are driven by gaps in our knowledge that are presented at genetic, metabolic, cellular, individual, and environmental (physical and social) levels.

DATA SYNTHESIS

As data collection on the cohort, animal experiments, and analyses proceed, results will be synthesized through a transdisciplinary approach.

CONCLUSION

Center investigators are addressing a large number of specific research questions related to early pubertal onset, which is an established risk factor for breast cancer. BCERC research findings aimed at the primary prevention of breast cancer will be disseminated to the scientific community and to the public by breast cancer advocates, who have been integral members of the research process from its inception.

Genetic polymorphisms of estrogen metabolizing enzyme and breast cancer risk in Thai women

Estrogen and its metabolites are believed to play important roles in breast cancer, and its determinants include both genetic and lifestyle factors. The objective of the study is to investigate the association of breast cancer risk in Thailand with genetic polymorphisms in several genes involved in estrogen synthesis and metabolism. Five hundred and seventy patients with histopathologically confirmed breast cancer and 497 controls were included in the present study. Forty single nucleotide polymorphisms (SNPs) in the CYP1A1, CYP1A2, CYP1B1, CYP17, CYP19, CYP2C9, CYP2C19, AhR, ESR1, PGR, ERRG, COMT, HSD17B1, HSD17B2, EPHX1 and NQO1 genes were genotyped. Association of genotypes with breast cancer risk was evaluated using multivariate logistic regression, which suggested an altered risk for the following SNPs [gene, odds ratio (OR) and 95% confidence interval are shown]: heterozygote carriers of rs4917623 [CYP2C19, OR = 1.38 (1.04-1.84)], rs2066853 [AhR, OR = 1.34 (1.02-1.76)] and rs1857407 [ERRG, (OR = 0.72 (0.55-0.96)]; homozygote carriers of rs762551 [CYP1A2, OR = 2.75 (1.47-5.14)], rs4917623 [CYP2C19, OR = 1.48 (1.00-2.19) and rs945453 [ERRG, OR = 1.66 (1.04-2.65)]. In addition, a stratified analysis by menopausal status indicated that the association of the CYP1A2 (rs762551) and CYP17 (rs743572) polymorphisms with breast cancer risk were mainly evident in premenopausal, while ERRG (rs1857407) was significant in postmenopausal women. These findings suggest that CYP1A2, CYP2C19, AhR, ERRG and CYP17 polymorphisms may play an important role in estrogen metabolism and modify individual susceptibility to breast cancer in Thai women.

Early life circumstances and their impact on menarche and menopause

Ages at menarche and menopause have been shown to be associated with adverse health outcomes in later life. For example, earlier menarche and later menopause have been independently linked to higher risk of breast cancer. Earlier menarche may also be associated with an increased risk of endometrial cancer, menstrual problems and adult obesity. Given the associations of ages at menarche and menopause with future health outcomes, it is important to establish what factors across life, and generations, may influence these. This article examines the associations of early life factors, namely birthweight, bodyweight and growth during childhood, childhood socioeconomic circumstances and psychosocial factors with ages at menarche and menopause. It examines possible explanations of the associations found, including life history theory, and discusses areas for future research.

Light-at-night, circadian disruption and breast cancer: assessment of existing evidence

BACKGROUND

Breast cancer incidence is increasing globally for largely unknown reasons. The possibility that a portion of the breast cancer burden might be explained by the introduction and increasing use of electricity to light the night was suggested >20 years ago.

METHODS

The theory is based on nocturnal light-induced disruption of circadian rhythms, notably reduction of melatonin synthesis. It has formed the basis for a series of predictions including that non-day shift work would increase risk, blind women would be at lower risk, long sleep duration would lower risk and community nighttime light level would co-distribute with breast cancer incidence on the population level.

RESULTS

Accumulation of epidemiological evidence has accelerated in recent years, reflected in an International Agency for Research on Cancer (IARC) classification of shift work as a probable human carcinogen (2A). There is also a strong rodent model in support of the light-at-night (LAN) idea.

CONCLUSION

If a consensus eventually emerges that LAN does increase risk, then the mechanisms for the effect are important to elucidate for intervention and mitigation. The basic understanding of phototransduction for the circadian system, and of the molecular genetics of circadian rhythm generation are both advancing rapidly, and will provide for the development of lighting technologies at home and at work that minimize circadian disruption, while maintaining visual efficiency and aesthetics. In the interim, there are strategies now available to reduce the potential for circadian disruption, which include extending the daily dark period, appreciate nocturnal awakening in the dark, using dim red light for nighttime necessities, and unless recommended by a physician, not taking melatonin tablets.

Prevention of oxidative DNA damage by bioactive berry components

The hormone 17ss-estradiol (E(2)) causes oxidative DNA damage via redox cycling of its metabolites such as 4-hydroxy estradiol (4E(2)). In this study, ACI rats (8 wk old) were fed either AIN-93M diet or diets supplemented with 0.5% each of mixed berries (strawberry, blueberry, blackberry, and red and black raspberry), blueberry alone (BB; 2.5%), or ellagic acid (EA; 400 ppm) from 2 wk prior to and up to 12 wk of E(2) treatment. The liver DNA was analyzed for the presence of 8-oxo-7,8-dihydroguanine (8-oxodG) and other polar adducts by 32P-postlabeling. Compared to sham treatment, E(2) significantly increased the levels of both 8-oxodG and P-1 subgroup (259% and 214%, respectively; P< 0.05). EA diet significantly reduced E(2)-induced levels of 8-oxodG, P-1, P-2, and PL-1 by 79, 63, 44, and 67%, respectively (P< 0.001). BB diet also significantly reduced the levels of P-1, P-2, and PL-1 subgroups by 77, 43, and 68%, respectively (P< 0.001). Mixed berries were, however, ineffective. In addition, aqueous extracts of berries (2%) and EA (100 microM) were tested for their efficacy in diminishing oxidative DNA adducts induced by redox cycling of 4E(2) catalyzed by copper chloride in vitro. EA was the most efficacious (90%), followed by extracts of red raspberry (70%), blueberry, and strawberry (50% each; P< 0.001).

Examining breast cancer growth and lifestyle risk factors: early life, childhood, and adolescence

The perinatal period, childhood, and adolescence are important intervals for breast cancer risk development. Endogenous estrogen exposure is thought to be highest in utero, and exposure to estrogens throughout life plays an important role in increasing breast cancer risk. Some evidence suggests that breast tissue is not fully differentiated until after the first full-term pregnancy; thus, breast tissue might be more susceptible to carcinogenic influences during early life and adolescence. Birth characteristics of the daughter, including gestational age, birth weight, and birth length are associated with maternal hormone levels during the index pregnancy, and birth size has been related to daughter's timing of puberty and adult breast cancer incidence. Furthermore, early life and adolescence are critical times for maturation of the hypothalamic pituitary ovarian axis, which regulates production of ovarian hormones including estrogen and progesterone. Childhood height, growth, diet, and body mass index (BMI) have also been associated with breast cancer risk later in life. Of the examined characteristics, we conclude that the available evidence is suggestive of a positive relationship of breast cancer risk with birth weight, birth length, and adolescent height, and an inverse relationship with gestational age and childhood BMI, although several inconsistencies exist in the literature. The best evidence for a relationship of adolescent diet and adult breast cancer risk is indirect, and the relationship of diet, weight status, and weight gain in childhood deserves further attention. The interaction of birth characteristics with established risk factors over the life course, such as age at menarche, in addition to gene-environment interactions, require more research. Further study is also needed to clarify the biologic mechanisms influencing the observed associations.

Association between age at menarche and risk of diabetes in adults: results from the EPIC-Norfolk cohort study

AIMS/HYPOTHESIS

Earlier age at menarche is associated with increased BMI and obesity risk from early childhood through to adulthood. We hypothesised that earlier age at menarche would also predict subsequent diabetes risk.

METHODS

This was a population-based prospective cohort study of 13,308 women, who were aged 40 to 75 years between 1993 and 1997 and participating in the Norfolk cohort of the European Prospective Investigation into Cancer and Nutrition (EPIC-Norfolk). We used data on age at menarche and ascertained diabetes incidence to 2005.

RESULTS

There were 734 cases of diabetes (363 incident and 371 prevalent cases). Mean age at menarche was lower in women with diabetes than in non-diabetic women (12.8 vs 13.0 years, p = 0.008). Compared with the earliest quintile (menarche at 8-11 years), women in the oldest quintile (menarche at 15-18 years) had lower BMI (25.5 vs 27.4 kg/m2, p < 0.0001) and a reduced risk of diabetes (OR 0.66 [95% CI 0.51-0.86] adjusted for age, family history, physical activity, smoking, occupational social class, parity and use of hormonal preparations). The association between age at menarche and diabetes was linear (adjusted OR 0.91 [95% CI 0.87-0.96] per 1 year later menarche) and appeared to be completely mediated by adult BMI or waist circumference (OR 0.98 [95% CI 0.93-1.03], further adjusted for BMI at age 40-75 years).

CONCLUSIONS/INTERPRETATION

Earlier age at menarche increases the risk of diabetes in women and this association appears to be mediated by increased adiposity. History of earlier menarche may help to identify women with increased subsequent risk of diabetes.

Parity and breastfeeding are protective against breast cancer in Nigerian women

As the relation between reproductive factors and breast cancer risk has not been systematically studied in indigenous women of sub-Saharan Africa, we examined this in a case–control study in Nigeria. In-person interviews were conducted using structured questionnaires to collect detailed reproductive history in 819 breast cancer cases and 569 community controls between 1998 and 2006. Logistic regression was used to estimate odds ratios (ORs) and 95% confidence intervals (CI). Compared with women with menarcheal age <17 years, the adjusted OR for women with menarcheal age ⩾17 years was 0.72 (95% CI: 0.54–0.95, P=0.02). Parity was negatively associated with risk (P-trend=0.02) but age at first live birth was not significant (P=0.16). Importantly, breast cancer risk decreased by 7% for every 12 months of breastfeeding (P-trend=0.005). It is worth noting that the distribution of reproductive risk factors changed significantly from early to late birth cohorts in the direction of increasing breast cancer incidence. Our findings also highlight the heterogeneity of breast cancer aetiology across populations, and indicate the need for further studies among indigenous sub-Saharan women.

Early life events and conditions and breast cancer risk: from epidemiology to etiology

Risk factors for breast cancer--documented by intensive epidemiological investigations and viewed in the context of general principles of carcinogenesis--can be integrated to an etiologic model comprising 3 principal components: the likelihood of breast cancer occurrence depends on the number of mammary tissue-specific stem cells, which is determined in early life; all growth-enhancing mammotropic hormones affect the rate of expansion of initiated clones; and while a pregnancy stimulates the replication of already initiated cells, it conveys long-term protection through differentiation of mammary tissue-specific stem cells. This perspective accommodates much of what is known about the epidemiology and natural history of breast cancer and highlights the role of early life in the origin of this cancer.

Timing of menarche and first full-term birth in relation to breast cancer risk

Ages at menarche and first birth are established risk factors for breast cancer. The interval between these ages may also affect risk, since the breast is more susceptible to carcinogenic insults during this period than during the parous period. However, few investigators have studied this relation. Using logistic regression, the authors evaluated associations between the timing of reproductive events and breast cancer risk among 4,013 cases and 4,069 controls enrolled in a multicenter, population-based US case-control study of White and African-American women (1994-1998). For White, parous premenopausal and postmenopausal women, those who had an interval of > or =16 years between the ages of menarche and first birth had 1.5-fold (95% confidence interval (CI): 1.0, 2.2) and 1.4-fold (95% CI: 1.1, 1.8) increased risks of breast cancer, respectively, in comparison with those who had < or =5 years between these ages. Adjusting for age at first birth altered these risk estimates somewhat, to odds ratios of 1.5 (95% CI: 0.8, 2.9) and 1.0 (95% CI: 0.6, 1.5), respectively. These associations were stronger for lobular and hormone-receptor-positive tumors but were absent among premenopausal African-American women. The authors conclude that the interval between age at menarche and age at first birth is associated with the risk of hormonally sensitive types of breast cancer, particularly among White women.

Menstrual and reproductive factors in relation to mammographic density: the Study of Women's Health Across the Nation (SWAN)

Menstrual and reproductive factors may increase breast cancer risk through a pathway that includes increased mammographic density. We assessed whether known or suspected menstrual and reproductive breast cancer risk factors were cross-sectionally associated with mammographic density, by measuring area of radiographic density and total breast area on mammograms from 801 participants in the Study of Women's Health Across the Nation (SWAN), a multi-ethnic cohort of pre- and early perimenopausal women. From multivariable linear regression, the following menstrual or reproductive factors were independently associated with percent mammographic density (area of dense breast/breast area): older age at menarche (beta=10.3, P<0.01, for >13 vs. <12 years), premenstrual cravings and bloating (beta=-3.36, P=0.02), younger age at first full-term birth (beta=-8.12, P<0.01 for <or=23 years versus no births), greater number of births (beta=-6.80, P<0.01 for >or=3 births versus no births), and premenopausal status (beta=3.78, P<0.01 versus early perimenopausal). Only number of births remained associated with percent density after adjustment for age, race/ethnicity, study site, body mass index (BMI), and smoking. In addition, stratified analyses revealed that the association with number of births was confined to women within the lowest BMI tertile (beta=-12.2, P<0.01 for >or=3 births versus no births). Our data support a mechanism for parity and breast cancer that involves mammographic density among pre- and early perimenopausal women that may be modified by body size.

Ovarian hyperstimulation induces centrosome amplification and aneuploid mammary tumors independently of alterations in p53 in a transgenic mouse model of breast cancer

Aneuploidy and genomic instability are common features of human cancers, including breast cancer; however, mechanisms by which such abnormalities develop are not understood. The exquisite dependence of the mammary gland on hormones for growth and development as well as hormonal contributions to breast cancer risk and progression suggest that tumorigenic mechanisms in the breast should be considered in the context of hormonal stimulation. We used transgenic mice that overexpress luteinizing hormone with subsequent ovarian hyperstimulation as a model to identify mechanisms involved in hormone-induced mammary cancer. Tumor pathology in these mice is highly variable, suggesting individual tumors undergo distinct initiating or promoting events. Supporting this notion, hormone-induced tumors display considerable chromosomal instability and aneuploidy, despite the presence of functional p53. The presence of extensive centrosome amplification in tumors and hyperplastic glands prior to tumor formation suggests that alterations in the ovarian hormonal milieu dysregulate the centrosome cycle in mammary epithelial cells, leading to aneuploidy and cancer.