Role of birthweight in the etiology of breast cancer

Fetal growth and childhood cancer: a population-based study

OBJECTIVE

The etiology of childhood cancers is largely unknown. Studies have suggested that birth characteristics may be associated with risk. Our goal was to evaluate the risk of childhood cancers in relation to fetal growth.

METHODS

We conducted a case-control study nested within Nordic birth registries. The study included cancer cases diagnosed in Denmark, Finland, Norway, and Sweden among children born from 1967 to 2010 and up to 10 matched controls per case, totaling 17,698 cases and 172,422 controls. Odds ratios (ORs) and 95% confidence intervals (95% CIs) were derived from conditional logistic regression.

RESULTS

Risks of all childhood cancers increased with increasing birth weight (P trend ≤ .001). Risks of acute lymphoid leukemia and Wilms tumor were elevated when birth weight was >4000 g and of central nervous system tumors when birth weight was >4500 g. Newborns large for gestational age were at increased risk of Wilms tumor (OR: 2.1 [95% CI: 1.2-3.6]) and connective/soft tissue tumors (OR: 2.1 [95% CI: 1.1-4.4]). In contrast, the risk of acute myeloid leukemia was increased among children born small for gestational age (OR: 1.8 [95% CI: 1.1-3.1]). Children diagnosed with central nervous system tumors at <1 year of age had elevated risk with increasing head circumference (P trend < .001). Those with head circumference >39 cm had the highest risk (OR: 4.7 [95% CI: 2.5-8.7]).

CONCLUSIONS

In this large, Nordic population-based study, increased risks for several childhood tumors were associated with measures of fetal growth, supporting the hypothesis that tumorigenesis manifesting in childhood is initiated in utero.

The prevalence of loss of imprinting of H19 and IGF2 at birth

Imprinted genes are monoallelically expressed according to the parent of origin and are critical for proper placental and embryonic development. Disruption of methylation patterns at imprinted loci resulting in loss of imprinting (LOI) may lead to serious imprinting disorders (e.g., Beckwith-Wiedemann syndrome) and is described in some cancers (e.g., Wilms' tumor). As most research has focused on children with cancer or other abnormal phenotypes, the imprinting status in healthy infants at birth has not been characterized. We examined the prevalence of H19 and IGF2 LOI at birth by allele-specific expression assays analysis on 114 human individuals. Overall expression and methylation analyses were performed on a subset of samples. We found that LOI of H19 was observed for 4% of individuals in cord blood and 3.3% in placenta, and for IGF2 of 22% of individuals in the cord blood and 0% in placenta. Interestingly, LOI status did not correspond to aberrant methylation levels of the imprinted DMRs or with changes in overall gene expression for the majority of individuals. Our observations suggest that LOI is present in phenotypically healthy infants. Determining a "normal" human epigenotype range is important for discovering factors required to maintain a healthy pregnancy and embryonic development.

Lasting effects on body weight and mammary gland gene expression in female mice upon early life exposure to n-3 but not n-6 high-fat diets

Exposure to an imbalance of nutrients prior to conception and during critical developmental periods can have lasting consequences on physiological processes resulting in chronic diseases later in life. Developmental programming has been shown to involve structural and functional changes in important tissues. The aim of the present study was to investigate whether early life diet has a programming effect on the mammary gland. Wild-type mice were exposed from 2 weeks prior to conception to 6 weeks of age to a regular low-fat diet, or to high-fat diets based on either corn oil or flaxseed oil. At 6 weeks of age, all mice were shifted to the regular low-fat diet until termination at 10 weeks of age. Early life exposure to a high-fat diet, either high in n-6 (corn oil) or in n-3 (flaxseed oil) polyunsaturated fatty acids, did not affect birth weight, but resulted in an increased body weight at 10 weeks of age. Transcriptome analyses of the fourth abdominal mammary gland revealed differentially expressed genes between the different treatment groups. Exposure to high-fat diet based on flaxseed oil, but not on corn oil, resulted in regulation of pathways involved in energy metabolism, immune response and inflammation. Our findings suggest that diet during early life indeed has a lasting effect on the mammary gland and significantly influences postnatal body weight gain, metabolic status, and signaling networks in the mammary gland of female offspring.

Redefining the impact of nutrition on breast cancer incidence: is epigenetics involved?

Breast cancer incidence is rising worldwide with an increase in aggressive neoplasias in young women. Possible factors involved include lifestyle changes, notably diet that is known to make an impact on gene transcription. However, among dietary factors, there is sufficient support for only greater body weight and alcohol consumption whereas numerous studies revealing an impact of specific diets and nutrients on breast cancer risk show conflicting results. Also, little information is available from middle- and low-income countries. The diversity of gene expression profiles found in breast cancers indicates that transcription control is critical for the outcome of the disease. This suggests the need for studies on nutrients that affect epigenetic mechanisms of transcription, such as DNA methylation and post-translational modifications of histones. In the present review, a new examination of the relationship between diet and breast cancer based on transcription control is proposed in light of epidemiological, animal and clinical studies. The mechanisms underlying the impact of diets on breast cancer development and factors that impede reaching clear conclusions are discussed. Understanding the interaction between nutrition and epigenetics (gene expression control via chromatin structure) is critical in light of the influence of diet during early stages of mammary gland development on breast cancer risk, suggesting a persistent effect on gene expression as shown by the influence of certain nutrients on DNA methylation. Successful development of breast cancer prevention strategies will require appropriate models, identification of biological markers for rapid assessment of preventive interventions, and coordinated worldwide research to discern the effects of diet.

Dichlorodiphenyltrichloroethane (DDT), DDT metabolites and pregnancy outcomes

Organochlorine pesticides (OCPs) are persistent endocrine disruptors. OCPs cross the placenta; this prenatal exposure has been associated with adverse pregnancy outcomes. We investigated associations between prenatal exposure to OCPs and gestational age and birth weight in 600 infants born between 1960 and 1963. The primary OCP was 1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane (p,p'-DDT), its primary metabolite, 1,1'-dichloro-2,2'-bis(p-chlorophenyl)ethylene (p,p'-DDE) and the contaminant, 1,1,1-trichloro-2-(p-chlorophenyl)-2-(o-chlorophenyl)-ethane (o,p'-DDT). Regression analysis indicated that for each natural log unit increase in p,p'-DDT, birth weight increased by 274 g (95% CI: 122, 425) when controlling for p,p'-DDE and o,p'-DDT. At a given level of p,p'-DDT exposure, o,p'-DDT and p,p'-DDE were associated with decreased birth weight. p,p'-DDE was negatively associated with length of gestation, controlling for p,p'-DDT and o,p'-DDT. These findings suggest opposing associations between exposure to p,p'-DDT and p,p'-DDE and birth weight. We did not find evidence to support mediation by maternal thyroid hormone status nor that the association differed by sex.

Impact of body mass index on breast cancer in accordance with the life-stage of women

A large amount of epidemiological evidence suggests that the impact of body weight on breast cancer risk should be heterogeneous throughout the life-stage of women. At birth, high weight has been positively associated with an increased risk of breast cancer. While, the body mass index (a relative body weight; BMI kg/m²) has been inversely associated with breast cancer risk among pre-menopausal women. The inverse trend had been observed in both Western and Asian population, with a relatively lower percentage of obesity and higher percentage of leanness, suggested that the inverse trend could be explained not only by the protective impact due to obesity, but also by the increased risk of breast cancer due to leanness. Among post-menopausal women, however, an elevated BMI has been positively associated with the development of breast cancer, particularly in the cases of estrogen receptor-positive (ER+) and progesterone receptor-positive (PR+) tumors. Currently, the mechanisms underlying the heterogeneous impacts between BMI on breast cancer risk and the life-stage of women remain poorly understood. We reviewed several proposed biological mechanisms that may contribute to the various impacts of relative body weight on breast cancer risk across life-stage. We also discussed the impact of BMI upon the outcome of endocrine therapy, particularly for aromatase inhibitor, in breast cancer patients. To prevent breast cancer incidence and recurrence, the desirable BMI of women may differ throughout their life-stage. To define the underlying mechanism for the various impacts of BMI in the context of breast cancer across various female life stages, further studies will be required.

Early nutrition impact on the insulin-like growth factor axis and later health consequences

PURPOSE OF REVIEW

There is increasing interest in the role of insulin-like growth factor-I (IGF-I) in the relation between early growth and later risk of noncommunicable diseases (NCDs). This review presents and discusses a selection of recent publications on this topic.

RECENT FINDINGS

Nutrition during pregnancy and in preterm infants has an influence on IGF-I. Breastfeeding is associated with lower IGF-I values and the effect of early protein intake was confirmed in a large intervention study. IGF-I levels are associated with early obesity, but the relation is complex and differs with age. Further studies and reviews support that there is a programming of the IGF axis, with higher levels during early life being associated with lower levels in adulthood, which is likely to influence the risk of NCDs later in life.

SUMMARY

Recent studies support that IGF-I plays an important role in the complex association between early diet, growth and later health, but more studies are needed to better understand the role of IGF-I, especially in the early development of obesity. Studies with data on how IGF-I is influenced by early diet in studies of preterm infants and young children with undernutrition from low-income countries will be helpful in recommending optimal diets.

How the Newcastle Thousand Families birth cohort study has contributed to the understanding of the impact of birth weight and early life socioeconomic position on disease in later life

Much has been made of the potential influence of birth weight and early socioeconomic disadvantage in influencing adult health, but little has been published in terms of how important these associations may be with respect to exposures throughout the lifecourse. The objective of this review is to describe the contributions of the Newcastle Thousand Families Study in understanding the relative impacts of factors in early life, particularly birth weight and socio-economic position at birth, in influencing health in later life. The Newcastle Thousand Families Study is a prospective birth cohort established in 1947. It originally included all births to mothers resident in Newcastle upon Tyne, in northern England, in May and June of that year. Study members were followed extensively throughout childhood and intermittently in adulthood. At the age of 49-51 years, study members underwent a large-scale follow-up phase enabling an assessment of how early life may influence their later health, and also incorporating adult risk factors which enabled the relative contributions of factors at different stages of life to be assessed. While some findings from the study do support birth weight and early socio-economic position having influences on adult health status, the associations are generally small when compared to risk factors later in life. Using path analyses on longitudinal data of this nature enables mediating pathways between early life and later health to be assessed and if more studies were to take this approach, the relative importance of early life on adult disease risk could be better understood.

Novel measurements of mammary stem cells in human umbilical cord blood as prospective predictors of breast cancer susceptibility in later life

BACKGROUND

The size of the breast stem-cell pool could underlie the intrauterine roots of breast cancer. We studied whether breast stem cells exist in umbilical cord blood and if they correlate with hematopoietic stem-cell measurements that have been positively associated with perinatal risk factors for breast cancer.

SUBJECTS AND METHODS

We isolated mononuclear cells from umbilical cord blood of 170 singleton full-term pregnancies and determined, by reverse transcription polymerase chain reaction, the presence of genes of putative breast epithelial stem-cell/progenitor markers [including epithelial cell adhesion molecule (EpCAM), CD49f (α6-integrin), CD117 (c-kit receptor), CD24, and CD29 (β1-integrin)]. By immunocytochemistry, we colocalized protein expressions of EpCAM+CD49f+, CD49f+CD24+, and CD24+CD29+. We correlated concentrations of putative breast stem-cell/progenitor subpopulations, quantified by flow cytometry, with concentrations of hematopoietic stem cells.

RESULTS

Mammary stem-cell phenotypes were identified in umbilical cord blood. The measured EpCAM+ subpopulation was positively correlated with concentrations of CD34+ and CD34+CD38- hematopoietic stem cells (both P=0.006). Additionally, EpCAM+CD49f+ and CD49f+CD24+ subpopulations were positively correlated to the CD34+ cells (P=0.03 and 0.008, respectively).

CONCLUSION

The positive association between measurable breast and hematopoietic stem cells in human umbilical cord blood suggests plausible mechanisms for a prenatal influence on breast cancer risk.

Benefits and risks of ovarian function and reproduction for cancer development and prevention

Ovarian function and menstrual cycle disturbances, pregnancy, and reproductive medicine procedures can either increase gynecological cancer risk or prevent cancer development. For ovarian cancer development, there are two hypotheses, which are connected with ovulation and gonadotropin secretion. Most of the ovarian cancers seem to be derived from displaced ovarian surfice epithelial cells. One year of ovulatory cycles increases the ovarian cancer risk by 6%. Ovulation between 22 and 29 years of age causes the highest risk increase per year. In contrast, progesterone or progestins appear to create protection. Lifestyle can affect or modify ovarian cancer risk. Breast cancer risk is very much related to age of menarche and menopause, pregnancy, and breast feeding. All of which are related to ovarian function and progestogenic impact that translates either into breast cancer risk increase or decrease. This is modified by body mass index, physical activity, and lifestyle in general. The risk of endometrial cancer is most closely related to endogenous progesterone during the menstrual cycle and pregnancy or by exogenous progestogens as in oral contraceptives. These effects are progestogen dose and time dependent. Endometrial cancer risk can also be increased by estrogen-producing tumors or long-term estrogen treatment.

Birth weight and other prenatal factors and risk of breast cancer in Asian-Americans

Little is known about the role of birth weight and other prenatal factors in the etiology of breast cancer in Asian-Americans. We investigated the relation between birth weight and other prenatal factors and breast cancer risk in a population-based case-control study in Los Angeles County that included 2,259 Asian-American women with incident, histologically confirmed breast cancer and 2,019 control women, who were frequency matched to cases on age, Asian ethnicity, and neighborhood of residence. Breast cancer risk nearly doubled (odds ratio (OR) = 1.97, 95% confidence interval (CI) = 1.15-3.39) among those with high (≥ 4000 g) birth weight compared to those with low (<2500 g) birth weight after adjusting for age at menarche, parity, adult body mass index, and other covariates. Risk increased 8% per 500 g increase in birth weight (P trend = 0.10). We observed a significant relationship between birth weight and age at menarche in both cases and controls. Mean birth weight was higher (2948 g) for control women who had early menarche (age ≤ 11 years) compared to those who had menarche late (age ≥ 15 years) (2807 g) (P trend = 0.016); results were similar among case patients (P trend = 0.020). Older maternal age was also a risk factor; risk increased by 6% (95% CI = 1.01-1.12) per 5 years increase in maternal age with adjustment for parity and other risk factors. Our results support the hypothesis that high birth weight and older maternal age at pregnancy may have contributed to the rising breast cancer incidence in Asian-Americans.

Maternal nutritional status, C(1) metabolism and offspring DNA methylation: a review of current evidence in human subjects

Evidence is growing for the long-term effects of environmental factors during early-life on later disease susceptibility. It is believed that epigenetic mechanisms (changes in gene function not mediated by DNA sequence alteration), particularly DNA methylation, play a role in these processes. This paper reviews the current state of knowledge of the involvement of C₁ metabolism and methyl donors and cofactors in maternal diet-induced DNA methylation changes in utero as an epigenetic mechanism. Methyl groups for DNA methylation are mostly derived from the diet and supplied through C₁ metabolism by way of choline, betaine, methionine or folate, with involvement of riboflavin and vitamins B₆ and B₁₂ as cofactors. Mouse models have shown that epigenetic features, for example DNA methylation, can be altered by periconceptional nutritional interventions such as folate supplementation, thereby changing offspring phenotype. Evidence of early nutrient-induced epigenetic change in human subjects is scant, but it is known that during pregnancy C₁ metabolism has to cope with high fetal demands for folate and choline needed for neural tube closure and normal development. Retrospective studies investigating the effect of famine or season during pregnancy indicate that variation in early environmental exposure in utero leads to differences in DNA methylation of offspring. This may affect gene expression in the offspring. Further research is needed to examine the real impact of maternal nutrient availability on DNA methylation in the developing fetus.

Birthweight, maternal weight trajectories and global DNA methylation of LINE-1 repetitive elements

Low birthweight, premature birth, intrauterine growth retardation, and maternal malnutrition have been related to an increased risk of cardiovascular disease, type 2 diabetes mellitus, obesity, and neuropsychiatric disorders later in life. Conversely, high birthweight has been linked to future risk of cancer. Global DNA methylation estimated by the methylation of repetitive sequences in the genome is an indicator of susceptibility to chronic diseases. We used data and biospecimens from an epigenetic birth cohort to explore the association between trajectories of fetal and maternal weight and LINE-1 methylation in 319 mother-child dyads. Newborns with low or high birthweight had significantly lower LINE-1 methylation levels in their cord blood compared to normal weight infants after adjusting for gestational age, sex of the child, maternal age at delivery, and maternal smoking during pregnancy (p = 0.007 and p = 0.036, respectively), but the magnitude of the difference was small. Infants born prematurely also had lower LINE-1 methylation levels in cord blood compared to term infants, and this difference, though small, was statistically significant (p = 0.004). We did not find important associations between maternal prepregnancy BMI or gestational weight gain and global methylation of the cord blood or fetal placental tissue. In conclusion, we found significant differences in cord blood LINE-1 methylation among newborns with low and high birthweight as well as among prematurely born infants. Future studies may elucidate whether chromosomal instabilities or other functional consequences of these changes contribute to the increased risk of chronic diseases among individuals with these characteristics.

Body size in early life and adult levels of insulin-like growth factor 1 and insulin-like growth factor binding protein 3

Body size in early life has been associated with breast cancer risk. This may be partly mediated through the insulin-like growth factor (IGF) pathway. The authors assessed whether birth weight, body fatness at ages 5 and 10 years, and body mass index (BMI; weight (kg)/height (m)(2)) at age 18 years were associated with plasma concentrations of insulin-like growth factor 1 (IGF-1) and insulin-like growth factor binding protein 3 in 6,520 women aged 32-70 years at blood draw from the Nurses' Health Study (1990-2006) and Nurses' Health Study II (1997-2005). Birth weight, body fatness in childhood, and BMI at age 18 years were inversely associated with adult IGF-1 levels. For example, IGF-1 levels were 11.9% lower in women who reported being heaviest at age 10 years than in those who were leanest at age 10 (P-trend < 0.0001). Further, women who reported their birth weight as ≥10 pounds (≥4.5 kg) (vs. <5.5 pounds (<2.5 kg)) had 7.9% lower IGF-1 levels (P-trend = 0.002). Women whose BMI at age 18 years was ≥30 (vs. <20) had 14.1% lower IGF-1 levels (P-trend < 0.0001). Similar inverse associations were observed for insulin-like growth factor binding protein 3. These observations did not vary by adult BMI or menopausal status at blood draw. These findings suggest that altered IGF-1 levels in adulthood may be a mechanism through which early-life body size influences subsequent breast cancer risk.

Physical activity pattern and activity energy expenditure in healthy pregnant and non-pregnant Swedish women

BACKGROUND/OBJECTIVES

Energy costs of pregnancy approximate 320  MJ in well-nourished women, but whether or not these costs may be partly covered by modifications in activity behavior is incompletely known. In healthy Swedish women: (1) to evaluate the potential of the Intelligent Device for Energy Expenditure and Physical Activity (IDEEA) to assess energy expenditure during free-living conditions, (2) to assess activity pattern, walking pace and energy metabolism in pregnant women and non-pregnant controls, and (3) to assess the effect on energy expenditure caused by changes in physical activity induced by pregnancy.

SUBJECTS/METHODS

Activity pattern was assessed using the IDEEA in 18 women in gestational week 32 and in 21 non-pregnant women. Activity energy expenditure (AEE) was assessed using IDEEA, as well as using the doubly labelled water method and indirect calorimetry.

RESULTS

AEE using the IDEEA was correlated with reference estimates in both groups (r=0.4-0.5; P<0.05). Reference AEE was 0.9 MJ/24 h lower in pregnant than in non-pregnant women. Pregnant women spent 92 min/24 h more on sitting, lying, reclining and sleeping (P=0.020), 73 min/24 h less on standing (P=0.037) and 21 min/24 h less on walking and using stairs (P=0.049), and walked at a slower pace (1.1 ± 0.1 m/s versus 1.2±0.1 m/s; P=0.014) than did non-pregnant controls. The selection of less demanding activities and slower walking pace decreased energy costs by 720 kJ/24 h and 80 kJ/24 h, respectively.

CONCLUSION

Healthy moderately active Swedish women compensated for the increased energy costs of pregnancy by 0.9 MJ/24 h. The compensation was mainly achieved by selecting less demanding activities.

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.

The use of birth certificate data to reconstruct and validate self-reported birth address in a study of breast cancer and environment

PURPOSE

We conducted a study comparing the location of addresses recorded on birth certificates with self-reported birth addresses provided by adults who were participants in the Western New York Exposure and Breast Cancer (WEB) Study. We also evaluated whether birth certificate residence data may be used to reconstruct missing self-reported birth residence information.

METHODS

Subjects were selected from WEB study participants born in Western New York State between 1920 and 1964 for whom we were able to obtain a New York State birth certificate. Addresses were geocoded and mean distance and SD between self-reported and certificate addresses were calculated.

RESULTS

Our findings indicate good agreement between self-reported and birth certificate addresses (77% are within 0.25 mile difference), and no difference in recall for cases compared with controls.

CONCLUSIONS

This study provides evidence that self-reported and birth certificate-based addresses may be used together to achieve increased accuracy of historical records in early life when place of birth is used as a proxy for early life environment in relation to the development of breast cancer or other chronic diseases.

Height at diagnosis and birth-weight as risk factors for osteosarcoma

OBJECTIVES

Osteosarcoma typically occurs during puberty. Studies of the association between height and/or birth-weight and osteosarcoma are conflicting. Therefore, we conducted a large pooled analysis of height and birth-weight in osteosarcoma.

METHODS

Patient data from seven studies of height and three of birth-weight were obtained, resulting in 1,067 cases with height and 434 cases with birth-weight data. We compared cases to the 2000 US National Center for Health Statistics Growth Charts by simulating 1,000 age- and gender-matched controls per case. Adjusted odds ratios (ORs) and 95% confidence intervals (CIs) for associations between height or birth-weight and risk of osteosarcoma for each study were estimated using logistic regression. All of the case data were combined for an aggregate analysis.

RESULTS

Compared to average birth-weight subjects (2,665-4,045 g), individuals with high birth-weight (≥ 4,046 g) had an increased osteosarcoma risk (OR 1.35, 95% CI 1.01-1.79). Taller than average (51st - 89th percentile) and very tall individuals (≥ 90th percentile) had an increased risk of osteosarcoma (OR 1.35, 95% CI 1.18-1.54 and OR 2.60, 95% CI 2.19-3.07, respectively; P (trend) < 0.0001).

CONCLUSIONS

This is the largest analysis of height at diagnosis and birth-weight in relation to osteosarcoma. It suggests that rapid bone growth during puberty and in utero contributes to OS etiology.

Mothers' pre-pregnancy BMI and weight gain during pregnancy and risk of breast cancer in daughters

Previous studies have established that higher birthweight is associated with increased risk of breast cancer. However, the mechanisms underlying this association remain unclear. We explored whether maternal pregnancy weight gain and pre-pregnancy body mass index (BMI), which influence birthweight, are associated with risk of breast cancer in offspring. The Nurses' Mothers case-control study of breast cancer was nested in the Nurses' Health Study I and II cohorts. Mothers of 814 nurses with and 1,809 nurses without breast cancer completed questionnaires with information on pre-pregnancy height and weight, pregnancy weight gain, and other aspects of their pregnancies with the nurse daughters. We calculated odds ratios for breast cancer using conditional logistic regression. Mean pregnancy weight gain was 23 lb, and average pre-pregnancy BMI was 21 kg/m². Mothers' weight gain during pregnancy was not associated with the daughters' risk of breast cancer. Compared to women whose mothers gained 20-29 lb, women whose mothers gained less than 10 lb had a relative risk of 0.92 (95% confidence interval [CI]: 0.62-1.36), adjusting for the age of the nurses. Women whose mothers gained 40 or more pounds had a relative risk of 0.82 (95% CI: 0.55-1.23). Mothers' pre-pregnancy BMI was not associated with the daughters' risk of breast cancer. Women whose mothers had a pre-pregnancy BMI of 30 or more had a relative risk of 0.77 (95% CI: 0.34-1.74) compared to those with BMI less than 20. Additional adjustment for prenatal factors or for nurses' characteristics later in life had no effect on the results. The association between birthweight and breast cancer risk is likely due to factors independent of mothers' weight gain during pregnancy or pre-pregnancy BMI. Because BMIs and pregnancy weight gains were lower in this population than today, we cannot rule out associations for very high pre-pregnancy BMIs or pregnancy weight gains.

Developmental and environmental origins of breast cancer: DDT as a case study

More than 20 studies of serum "DDT" and breast cancer have found little support for the hypothesis that exposure influences risk of breast cancer. However, studies share common limitations including the inability to account for exposure in early life when the breast may be most vulnerable and the inability to measure exposure to the primary components of commercial DDT. This paper (1) summarizes evidence regarding critical windows of exposure for breast cancer (2) summarizes lessons learned from initial efforts to study DDT and breast cancer (3) reviews evidence from the Child Health and Development Studies (CHDS) where exposure was measured in young women using blood samples obtained during active exposure, 1-3 days after delivery and (4) suggests approaches for human studies that might advance understanding of environmental stressors in the developmental origins of disease.

Using epidemiology and genomics to understand osteosarcoma etiology

Osteosarcoma is a primary bone malignancy that typically occurs during adolescence but also has a second incidence peak in the elderly. It occurs most commonly in the long bones, although there is variability in location between age groups. The etiology of osteosarcoma is not well understood; it occurs at increased rates in individuals with Paget disease of bone, after therapeutic radiation, and in certain cancer predisposition syndromes. It also occurs more commonly in taller individuals, but a strong environmental component to osteosarcoma risk has not been identified. Several studies suggest that osteosarcoma may be associated with single nucleotide polymorphisms in genes important in growth and tumor suppression but the studies are limited by sample size. Herein, we review the epidemiology of osteosarcoma as well as its known and suspected risk factors in an effort to gain insight into its etiology.

Epigenetics meets endocrinology

Although genetics determines endocrine phenotypes, it cannot fully explain the great variability and reversibility of the system in response to environmental changes. Evidence now suggests that epigenetics, i.e. heritable but reversible changes in gene function without changes in nucleotide sequence, links genetics and environment in shaping endocrine function. Epigenetic mechanisms, including DNA methylation, histone modification, and microRNA, partition the genome into active and inactive domains based on endogenous and exogenous environmental changes and developmental stages, creating phenotype plasticity that can explain interindividual and population endocrine variability. We will review the current understanding of epigenetics in endocrinology, specifically, the regulation by epigenetics of the three levels of hormone action (synthesis and release, circulating and target tissue levels, and target-organ responsiveness) and the epigenetic action of endocrine disruptors. We will also discuss the impacts of hormones on epigenetics. We propose a three-dimensional model (genetics, environment, and developmental stage) to explain the phenomena related to progressive changes in endocrine functions with age, the early origin of endocrine disorders, phenotype discordance between monozygotic twins, rapid shifts in disease patterns among populations experiencing major lifestyle changes such as immigration, and the many endocrine disruptions in contemporary life. We emphasize that the key for understanding epigenetics in endocrinology is the identification, through advanced high-throughput screening technologies, of plasticity genes or loci that respond directly to a specific environmental stimulus. Investigations to determine whether epigenetic changes induced by today's lifestyles or environmental 'exposures' can be inherited and are reversible should open doors for applying epigenetics to the prevention and treatment of endocrine disorders.

Relationship of folate, vitamin B12 and methylation of insulin-like growth factor-II in maternal and cord blood

BACKGROUND/OBJECTIVE

One of the speculated mechanisms underlying fetal origin hypothesis of breast cancer is the possible influence of maternal environment on epigenetic regulation, such as changes in DNA methylation of the insulin-like growth factor-2 (IGF2) gene. The aim of the study is to investigate the relationship between folate, vitamin B(12) and methylation of the IGF2 gene in maternal and cord blood.

SUBJECTS/METHODS

We conducted a cross-sectional study to measure methylation patterns of IGF2 in promoters 2 (P2) and promoters 3 (P3).

RESULTS

The percentage of methylation in IGF2 P3 was higher in maternal blood than in cord blood (P<0.0001), whereas the methylation in P2 was higher in cord blood than in maternal blood (P=0.016). P3 methylation was correlated between maternal and cord blood (P<0.0001), but not P2 (P=0.06). The multivariate linear regression model showed that methylation patterns of both promoters in cord blood were not associated with serum folate levels in either cord or maternal blood, whereas the P3 methylation patterns were associated with serum levels of vitamin B(12) in mother's blood (mean change (MC)=-0.22, P=0.0014). Methylation patterns in P2 of maternal blood were associated with serum levels of vitamin B(12) in mother's blood (MC=-0.23, P=0.012), exposure to passive smoking (MC=0.46, P=0.034) and mother's weight gain during pregnancy (MC=0.23, P=0.019).

CONCLUSIONS

The study suggests that environment influences methylation patterns in maternal blood, and then the maternal patterns influence the methylation status and levels of folate and vitamin B(12) in cord blood.

Global DNA methylation levels in girls with and without a family history of breast cancer

Lower levels of global DNA methylation in white blood cell (WBC) DNA have been associated with adult cancers. It is unknown whether individuals with a family history of cancer also have lower levels of global DNA methylation early in life. We examined global DNA methylation in WBC (measured in three repetitive elements, LINE1, Sat2 and Alu, by MethyLight and in LINE1 by pyrosequencing) in 51 girls ages 6-17. Compared to girls without a family history of breast cancer, methylation levels were lower for all assays in girls with a family history of breast cancer, and statistically significantly lower for Alu and LINE1 pyrosequencing. After adjusting for age, body mass index (BMI), and Tanner stage, only methylation in Alu was associated with family history of breast cancer. If these findings are replicated in larger studies, they suggest that lower levels of global WBC DNA methylation observed later in life in adults with cancer may also be present early in life in children with a family history of cancer.

Trends of abnormal birthweight among full-term infants in Newfoundland and Labrador

OBJECTIVES

The objective of this study was to investigate whether any observed trends in birthweight are accompanied by changes in maternal sociodemographic characteristics, including age, marital status, and education.

METHODS

We conducted a population-based study of term singletons born in Newfoundland and Labrador, Canada, between 1992 and 2005 (N = 66,638). Large-sample significance tests for two population proportions were used to test whether differences in mean birthweight, the proportion of low and high birthweight infants, and differences in maternal socio-demographic characteristics between 1992-95 and 2002-05 were statistically significant. Chi-square tests were used to test for associations between birthweight group and maternal age, education and marital status. Multivariate logistic regression was used to examine the interaction of these effects across time periods.

RESULTS

Of the 66,638 infants included in the study, 54,256 (81.4%) were born in the normal birthweight range (2500-4000 grams) while 11,305 (17.0%) were high birthweight (> 4000 grams) and 1,077 (1.6%) were low birthweight (< 2500 grams). The rate of low birthweight significantly decreased from 1992 to 1995 compared to the period 2002 to 2005 (1.9% to 1.3%: p < 0.01). The rate of high birthweight significantly increased over the same two time periods (16.2% to 17.5%: p < 0.01). Mean birthweight increased from 3529 grams to 3566 grams (p < 0.01). Compared to women who had babies from 1992 to 1995, women who gave birth from 2002 to 2005 were more likely to be older, have higher levels of education, and never have been married. Birthweight outcomes were significantly associated with mother's age, education and marital status.

CONCLUSION

Changes in maternal demographics are associated with the upward shift in birthweight in Newfoundland and Labrador.

Birth characteristics and age at menarche: results from the dietary intervention study in children (DISC)

OBJECTIVE

To examine whether birth weight, birth length, and gestational age are individually associated with age at menarche.

METHODS

Analyses were conducted using data from n = 278 female participants in the Dietary Intervention Study in Children (DISC). Age at menarche was prospectively collected as part of the original DISC investigation. DISC participants self-reported birth weight, birth length, and gestational age with assistance from their mothers and other records as part of the DISC06 Follow-up Study at ages 25-29. Linear regression was used to estimate the association of birth characteristics and age at menarche.

RESULTS

Birth weight was positively associated with age at menarche (p <or= 0.01) in multiple regression analyses after controlling for BMI-for-age percentile, race and DISC treatment group. No statistically significant relationships were detected between either length or gestational age and age at menarche.

CONCLUSIONS

Higher birth weight may be associated with a modest delay in age at menarche.

Gender-specific differences in birthweight and the odds of puberty: NHANES III, 1988-94

The association between birthweight and the odds ratio (OR) of pubertal status in girls aged between 8 and 11 and in boys aged between 8 and 12 was examined using the 1988-94 Third National Health and Nutrition Examination Survey (NHANES III). Girls (n = 956), and boys (n = 1199), who had data on birthweight and Tanner staging were included. Maternal-reported birthweight, smoking in pregnancy and other information were provided in a home interview, while Tanner staging to assess pubertal status was part of a medical examination. Multiple logistic regression models were computed for the endpoints of the OR [95% confidence interval (CI)] of being Tanner Stage 2+ vs. 1 or being 2+ vs. 1 in an asynchronous pubertal pathway after adjustment for the complex sampling design of NHANES, age, race, height and body mass index (BMI). Birthweight was not associated with the OR of Tanner stage 2+ among girls; however, boys who were low birthweight (<2500 g) and boys born higher than average birthweight (3500-3999 g) were more likely to be Tanner stage 2+ than 1. Childhood BMI was associated with the OR of having entered puberty among girls, but not boys. In an analysis of asynchronous maturation, girls born at high birthweight (>4000 g) were more likely to have breast development 3+ than girls of normal birthweight, OR = 3.18 [95% CI 1.39, 8.25]. Thus, the birthweight-puberty association varies by gender and by pubertal pathway. Our findings need replication in prospective longitudinal studies, and research to understand the mechanisms underlying the relation of early life exposures to cancer risk.

Risk of breast cancer among daughters of mothers with diabetes: a population-based cohort study

Introduction

Diabetes during pregnancy is related to enhanced fetal growth, which has been associated with increased breast cancer risk. Whether daughters of mothers with a diagnosis of diabetes have an increased risk of breast cancer is not known.

Methods

We performed a retrospective cohort study of daughters of mothers with diabetes by linkage of the Swedish Multigeneration, Cause-of-Death and Patient Register between 1952 and 2005. Breast cancer cases were ascertained by linkage with the Swedish Cancer Register between 1958 and 2005. Standardized incidence ratios (SIRs) of breast cancer were calculated assuming a Poisson distribution for the observed cases.

Results

We identified 291,360 daughters of mothers with a diagnosis of diabetes before or after birth between 1952 and 2005. Among the daughters, 7,956 cases of breast cancer were diagnosed between 1964 and 2005. The total time of follow-up was 12,173,821 person years. The expected number of breast cancer cases was 9,204, resulting in an SIR of 0.86 (95% CI, 0.85 to 0.88). The decrease in risk associated with maternal diabetes was stronger for premenopausal (< 55 years of age) than postmenopausal (≥ 55 years of age) breast cancer (SIR 0.83 and 0.91, respectively). Among daughters of mothers with diabetes, a history of breast cancer in the mother increased the risk of breast cancer in the daughter (SIR 1.43, 1.32 to 1.54).

Conclusions

Daughters of mothers with a lifetime history of diabetes were at a decreased risk of breast cancer. The strongest negative association was found among premenopausal breast cancer.

Birth weight and mammographic density among postmenopausal women in Sweden

Birth weight is a significant predictor of breast cancer risk in adult life and mammary gland mass could be an intermediate stage in this long process. We have studied the association of birth size measurements with mammographic density, a marker of mammary gland mass. For a population-based sample of 893 postmenopausal women without previous cancer in Sweden, we retrieved information on birth size from birth records and their most recent mammography. Film mammograms of the medio-lateral oblique view were digitized and the Cumulus software was used for computer-assisted semi-automated thresholding of mammographic density. Results were analyzed using generalized linear models controlling for possible confounders. Mean percent mammographic density increased when comparing the extreme categories of birth weight (from 15.6% to 18.6%) and head circumference (from 15.5% to 20.4%), and the corresponding linear trends were statistically significant (p values 0.02 and 0.007, respectively). The associations were particularly strong when the cutoff for high versus low mammographic density was set at the relatively high value of 50%. Compared to women weighing 3001-3500 grams at birth, women with birth weights >4000g were at almost 3-fold risk of developing high mammographic density (odds ratio: 2.9, 95% confidence interval 1.1 to 7.9). No association with mammographic density was evident with respect to birth length which, however, is known to be less accurately measured. These results indicate that adult breast density, a powerful predictor of breast cancer risk, has intrauterine roots, as reflected in birth size.

Birth weight, breast cancer susceptibility loci, and breast cancer risk

BACKGROUND

There is considerable evidence that birth weight is positively associated with breast cancer risk, and seven single-nucleotide polymorphisms (SNPs) have been conclusively associated with this risk. We have hypothesized that breast cancer susceptibility loci may have a greater influence on breast cancer risk among women with higher birth weight, who are expected to have a larger pool of mammary stem cells that are susceptible to malignant transformation.

PATIENTS AND METHODS

In the context of a nationwide, population-based case-control study in Sweden, we retrieved recorded birth weight for 693 breast cancer cases and 747 control women who were also genotyped for most or all of the seven recently documented breast cancer susceptibility SNPs: rs2981582, rs12443621, rs8051542, rs3803662, rs889312, rs13281615, and rs3817198.

RESULTS

We grouped heterozygotes with homozygotes for the wild-type allele, and we found a marginally significant interaction (p~0.07) between birth weight and rs2981582 (FGFR2), the genotype repeatedly identified as the top hit in genome-wide association studies. There were similar, though not significant, patterns for the other six SNPs.

CONCLUSIONS

Although our findings require confirmation, we found suggestive evidence that genetic susceptibility modifies the positive association of birth weight with breast cancer.

Validity of self-reported birth weight by adult women: sociodemographic influences and implications for life-course studies

Life-course epidemiologic studies frequently obtain data on perinatal and childhood factors through adult self-report. Data from a prospective US birth cohort of 262 women, born between 1959 and 1963 (average age at adult follow-up, 41.8 years), were used to assess the validity of self-reported birth weight category by sociodemographic characteristics. The effect of reporting error on the associations of birth weight with childhood and adult body mass index was evaluated by comparing the estimates of associations from linear regression analyses. The level of agreement between the birth weight category reported by 85% of the participants and the birth weight recorded at the time of birth was moderate to good (sensitivity = 73%, weighted kappa = 0.67). The validity varied by birth weight category (sensitivity range = 58%-81% for the lowest and highest birth weight category, respectively) and was highest for participants who were white, of lower childhood family income, and born to older mothers. Despite this moderate to good validity, the associations of birth weight with childhood and adult body mass index were attenuated and no longer statistically significant when self-reported birth weight was used. In conclusion, birth weight reported in middle adult life is measured with error, limiting its utility for detecting modest associations with health in later life periods.

Pubertal development in Mexican American girls: the family's perspective

Mexican American (MA) girls are entering puberty earlier than in the past, yet few studies have explored the perceptions surrounding puberty among this group. We conducted separate focus groups for fathers, mothers, and daughters aged 6 to 12 years to explore perceptions of body image, pubertal development, communications, and sources of puberty-related information in MA participants. Our results revealed parental concerns about daughters' weight and pubertal development, as well as differences in their communication with their daughters. Although both parents willingly discussed pubertal issues concerning their daughters, mothers had a more active role in conveying pubertal information to daughters. Among the girls, there was a gap in knowledge about the pubertal process between the younger and older girls. Our findings present opportunities and challenges for addressing obesity as a pubertal risk factor in MA girls; however, more studies are needed to understand family beliefs and sociocultural dynamics surrounding puberty in MAs.

Birth weight-breast cancer revisited: is the association confounded by familial factors?

PURPOSE

The study aimed to investigate whether the association between birth weight and the risk of breast cancer can be confounded by familial factors, such as shared environment and common genes.

MATERIALS AND METHODS

Eligible were all female like-sexed twins of the Swedish Twin Registry, born during the period 1926-1958 and alive in 1973. Data were obtained from birth records, and the final study population with reliable birth weight data was made up of 11,923 twins. Hazard ratios (HR) for breast cancer according to birth weight were estimated through Cox regression, using robust SE to account for the dependence within twin pairs. Paired analysis was done to account for potential confounding by familial factors.

RESULTS

In the cohort analysis, a birth weight >or=3,000 g was associated with an increased risk of breast cancer diagnosed at or before 50 years [adjusted HR, 1.57; 95% confidence interval (95% CI), 1.03-2.42] but not with breast cancer with a later onset (adjusted HR, 0.80; 95% CI, 0.57-1.12). From >or=2,500 g, a 500-g increase in birth weight conferred a HR of 1.62 (95% CI, 1.16-2.27) for breast cancer diagnosed at or before 50 years. This risk remained in analysis within twin pairs (HR, 1.57; 95% CI, 1.00-2.48).

CONCLUSION

In the present study, findings indicate that the association between birth weight and breast cancer risk, seen only in women diagnosed early (<or=50 years), is not confounded by familial factors.

Impact of diet on breast cancer risk

PURPOSE OF REVIEW

Breast cancer is the most common female cancer in Western Europe and North America, and becoming an increasing problem in developing countries such as India and China. We review recent studies (published 1 January 2007-31 August 2008) on the impact of diet on breast cancer risk.

RECENT FINDINGS

Recent studies have focused on the controversial association for dietary fat and breast cancer as well as the role of newer aspects such as glycemic index, dietary patterns and diet-gene interactions. Evidence that some of the associations may be modified by oestrogen and progesterone receptor status has been presented. Still, only alcohol intake, being overweight and weight gain have shown consistent and strong positive associations with breast cancer risk. The reasons for the null or weak associations often observed regarding diet and breast cancer might be several. For example, there may be no causal association, or existing associations may be masked by measurement error, timing of dietary exposure and differences according to tumour characteristics or diet-gene interactions.

SUMMARY

Numerous epidemiological studies on diet and breast cancer have been published during our review period. Still, only alcohol intake, being overweight and weight gain have shown consistent and strong positive associations with breast cancer risk.

Insulin-like growth factor levels in cord blood, birth weight and breast cancer risk

Breast cancer incidence and birth weight are higher among Caucasian than Asian women, and birth size has been positively associated with breast cancer risk. Pregnancy hormone levels, however, have been generally lower in Caucasian than Asian women. We studied components of the insulin-like growth factor (IGF) system in cord blood from 92 singleton babies born in Boston, USA, and 110 born in Shanghai, China, in 1994–1995. Cord blood IGF-1 was significantly higher among Caucasian compared with Chinese babies (P<10⁻⁶). The opposite was noted for IGF-2 (P∼10⁻⁴). IGF-1 was significantly positively associated with birth weight and birth length in Boston, but not Shanghai. In contrast, stronger positive, though statistically non-significant, associations of IGF-2 with birth size were only evident in Shanghai. The associations of birth weight and birth length were positive and significant in taller women (for IGF-1 in Boston P∼0.003 and 0.03, respectively; for IGF-2 in Shanghai P∼0.05 and ∼0.04, respectively), among whom maternal anthropometry does not exercise strong constraints in foetal growth. The documentation of higher cord blood levels of IGF-1, a principal growth hormone that does not cross the placenta, among Caucasian than in Asian newborns is concordant with breast cancer incidence in these populations.

Energy balance, early life body size, and plasma prolactin levels in postmenopausal women

OBJECTIVE

We examined the relationships of prolactin with birth weight; childhood, adolescent and adult body size measures; adult physical activity and inactivity; and alcohol consumption among 1,423 postmenopausal women from the Nurses' Health Study.

METHODS

Information on exposures was collected on biennial questionnaires beginning in 1976. Blood was collected from 32,826 participants in 1990; prolactin was measured in a subset of women who were controls for a nested breast cancer case-control study. Generalized linear models were adjusted for assay batch, medication use at blood draw, and other potential predictors of prolactin.

RESULTS

No associations were observed for adult factors (p-trend >or= 0.17), body mass index at age 18, birth weight, or height (p-trend >or= 0.27). There was an inverse association between body size at ages 5 (p-trend = 0.03) and 10 (p-trend = 0.05) and prolactin, with levels 9% lower among women with the heaviest versus leanest average childhood body size. This association was more pronounced among women with a birth weight <7 pounds (p-trend = 0.004; p-interaction between birth weight and childhood body size = 0.01).

CONCLUSIONS

Our results suggest that few adult lifestyle risk factors are associated with prolactin levels in postmenopausal women; however, childhood body size may be a predictor of levels later in life.

Physical activity during pregnancy and age at menarche of the daughter

In utero exposures have been proposed as possible determinants of later disease risk. Given that a later age at menarche is a breast cancer risk factor, and that higher childhood physical activity has been associated with a later menarcheal age, it is possible that a pregnant mother's activity may also influence this outcome. The purpose of this study was to determine if a mother's physical activity during pregnancy is related to their daughter's menarcheal age. Participants of the Nurses' Health Study II reported their age at menarche to the nearest year, whereas their mothers (n=33,016) completed surveys regarding their health and lifestyle habits during their pregnancy with their daughters. Mothers reported their home, occupational, and leisure-time physical activities, as well as the activity of their daughters at ages 5 to 10 years. Using multiple linear regression analysis with adjustment for specific covariates including daughter's childhood body size, neither home nor occupational activity alone were associated with age at menarche of the daughter, but there was a direct association with leisure-time physical activity (P(trend)<0.001). Compared with women inactive in their leisure-time, women who were highly active had daughters with menarche 1.1 (95% confidence interval, 0.3-1.9) months later. Using a composite variable of both home and leisure-time activity, daughters of women who were highly active at home and in their leisure-time had daughters with menarche 3.1 (95% confidence interval, 0.4-5.9) months later than those who were highly inactive in both. Physical activity during pregnancy may be associated with a modest delay in menarcheal age in offspring.

Nutrition in early life, and risk of cancer and metabolic disease: alternative endings in an epigenetic tale?

There is substantial evidence which shows that constraints in the early life environment are an important determinant of risk of metabolic disease and CVD. There is emerging evidence that higher birth weight, which reflects a more abundant prenatal environment, is associated with increased risk of cancer, in particular breast cancer and childhood leukaemia. Using specific examples from epidemiology and experimental studies, this review discusses the hypothesis that increased susceptibility to CVD, metabolic disease and cancer have a common origin in developmental changes induced in the developing fetus by aspects of the intra-uterine environment including nutrition which involve stable changes to the epigenetic regulation of specific genes. However, the induction of specific disease risk is dependent upon the nature of the environmental challenge and interactions between the susceptibility set by the altered epigenome and the environment throughout the life course.

Neonatal growth and breast cancer risk in adulthood

Birth size of a woman has been positively associated with her breast cancer risk, particularly before menopause, but no study has investigated neonatal growth in relation to this risk. We conducted a case-control study nested within a population-based cohort of women, born in Sweden between 1901 and 1961, covering all 405 breast cancer patients and 1081 age- and hospital-matched controls, who were born after newborn charts became available. Compared to neonates who lost <200 g after birth and grew at a rate <25 g day(-1) after reaching postnatal weight nadir (ie, the minimum, before starting to regain weight), those who either lost >/=200 g after birth or grew >/=25 g day(-1) after nadir, or both, were at an approximately 50% increased breast cancer risk. The excess risk was striking and statistically significant among women below 50 years of age, but was not evident among older women. Immediate postnatal weight loss (an indicator of water loss, likely to reflect water retention associated with pregnancy hormones) as well as neonatal weight gain rate after the nadir (known to reflect growth hormone levels) was significantly positively associated with premenopausal breast cancer risk.

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.