Reproductive factors in the aetiology of breast cancer

Fetal loss and long-term maternal morbidity and mortality: A systematic review and meta-analysis

BACKGROUND

Evidence suggests common pathways between pregnancy losses and subsequent long-term maternal morbidity, rendering pregnancy complications an early chronic disease marker. There is a plethora of studies exploring associations between miscarriage and stillbirth with long-term adverse maternal health; however, these data are inconclusive.

METHODS AND FINDINGS

We systematically searched MEDLINE, EMBASE, AMED, BNI, CINAHL, and the Cochrane Library with relevant keywords and MeSH terms from inception to June 2023 (no language restrictions). We included studies exploring associations between stillbirth or miscarriage and incidence of cardiovascular, malignancy, mental health, other morbidities, and all-cause mortality in women without previous pregnancy loss. Studies reporting short-term morbidity (within a year of loss), case reports, letters, and animal studies were excluded. Study selection and data extraction were performed by 2 independent reviewers. Risk of bias was assessed using the Newcastle Ottawa Scale (NOS) and publication bias with funnel plots. Subgroup analysis explored the effect of recurrent losses on adverse outcomes. Statistical analysis was performed using an inverse variance random effects model and results are reported as risk ratios (RRs) with 95% confidence intervals (CIs) and prediction intervals (PIs) by combining the most adjusted RR, odds ratios (ORs) and hazard ratios (HRs) under the rare outcome assumption. We included 56 observational studies, including 45 in meta-analysis. There were 1,119,815 women who experienced pregnancy loss of whom 951,258 had a miscarriage and 168,557 stillbirth, compared with 11,965,574 women without previous loss. Women with a history of stillbirth had a greater risk of ischaemic heart disease (IHD) RR 1.56, 95% CI [1.30, 1.88]; p < 0.001, 95% PI [0.49 to 5.15]), cerebrovascular (RR 1.71, 95% CI [1.44, 2.03], p < 0.001, 95% PI [1.92, 2.42]), and any circulatory/cardiovascular disease (RR 1.86, 95% CI [1.01, 3.45], p = 0.05, 95% PI [0.74, 4.10]) compared with women without pregnancy loss. There was no evidence of increased risk of cardiovascular disease (IHD: RR 1.11, 95% CI [0.98, 1.27], 95% PI [0.46, 2.76] or cerebrovascular: RR 1.01, 95% CI [0.85, 1.21]) in women experiencing a miscarriage. Only women with a previous stillbirth were more likely to develop type 2 diabetes mellitus (T2DM) (RR: 1.16, 95% CI [1.07 to 2.26]; p < 0.001, 95% PI [1.05, 1.35]). Women with a stillbirth history had an increased risk of developing renal morbidities (RR 1.97, 95% CI [1.51, 2.57], p < 0.001, 95% [1.06, 4.72]) compared with controls. Women with a history of stillbirth had lower risk of breast cancer (RR: 0.80, 95% CI [0.67, 0.96], p-0.02, 95% PI [0.72, 0.93]). There was no evidence of altered risk of other malignancies in women experiencing pregnancy loss compared to controls. There was no evidence of long-term mental illness risk in women with previous pregnancy losses (stillbirth: RR 1.90, 95% CI [0.93, 3.88], 95% PI [0.34, 9.51], miscarriage: RR 1.78, 95% CI [0.88, 3.63], 95% PI [1.13, 4.16]). The main limitations include the potential for confounding due to use of aggregated data with variable degrees of adjustment.

CONCLUSIONS

Our results suggest that women with a history of stillbirth have a greater risk of future cardiovascular disease, T2DM, and renal morbidities. Women experiencing miscarriages, single or multiple, do not seem to have an altered risk.

Descriptive Study and Surgical Management Among Infiltrating Lobular Carcinoma Patients Admitted to King Abdulaziz Medical City From 2000 to 2017: A Retrospective Cross-Sectional Study

INTRODUCTION

Invasive lobular carcinoma (ILC) is the second most common histologic type of breast carcinoma. The etiology of ILC is unknown; however, many contributing risk factors have been suggested. Treatment of ILC can be divided into local and systemic. Our objectives were to assess the clinical presentations, risk factors, radiological findings, pathological types, and surgical options for patients with ILC treated at the national guard hospital. Identify the factors associated with metastasis and recurrence.

METHODS

Retrospective cross-sectional descriptive study at a tertiary care center in Riyadh. All adult patients aged 16 years and above, from different nationalities, and both genders, were diagnosed with ILC from 2000 to 2017 and followed up at KAMC. The sampling technique was a non-probability consecutive technique. Among 1066 patients identified, 91 patients were diagnosed with ILC over seventeen years study period.

RESULTS

The median age at the primary diagnosis was 50. On the clinical examination, 63 (71%) cases were found to have palpable masses which was the most suspicious finding. On radiology, the most encountered finding was speculated masses which were seen in 76 (84%). Regarding the pathology, unilateral breast cancer was seen in 82 while bilateral breast cancer was found only in eight. For the biopsy, a core needle biopsy was the most commonly used in 83 (91%) patients. The most documented surgery for ILC patients was a modified radical mastectomy. Metastasis in different organs was identified with the musculoskeletal system being the commonest site. Different significant variables were compared between patients with or without metastasis. Skin changes, post-operative invasion, estrogen, progesterone, and HER2 receptors were significantly associated with metastasis. Patients with metastasis were less likely to have conservative surgery. Regarding the Recurrence and five years survival, out of 62 cases, 10 had recurrence within five years, which was more prevalent in patients who had fine needle aspiration, excisional biopsy, and nulliparous patients.

CONCLUSION

To our knowledge, this is the first study to exclusively describe ILC in Saudi Arabia. The results of this current study are highly important, as these results provide baseline data of ILC in the capital city of Saudi Arabia.

Inter-Individual Variation in Response to Estrogen in Human Breast Explants

Exposure to estrogen is strongly associated with increased breast cancer risk. While all women are exposed to estrogen, only 12% are expected to develop breast cancer during their lifetime. These women may be more sensitive to estrogen, as rodent models have demonstrated variability in estrogen sensitivity. Our objective was to determine individual variation in expression of estrogen receptor (ER) and estrogen-induced responses in the normal human breast. Human breast tissue from female donors undergoing reduction mammoplasty surgery were collected for microarray analysis of ER expression. To examine estrogen-induced responses, breast tissue from 23 female donors were cultured ex- vivo in basal or 10 nM 17β-estradiol (E2) media for 4 days. Expression of ER genes (ESR1 and ESR2) increased significantly with age. E2 induced consistent increases in global gene transcription, but expression of target genes AREG, PGR, and TGFβ2 increased significantly only in explants from nulliparous women. E2-treatment did not induce consistent changes in proliferation or radiation induced apoptosis. Responses to estrogen are highly variable among women and not associated with levels of ER expression, suggesting differences in intracellular signaling among individuals. The differences in sensitivity to E2-stimulated responses may contribute to variation in risk of breast cancer.

Induced abortion and breast cancer: An updated meta-analysis

Different epidemiological studies have indicated conflicting information about the association of induced abortion (IA) with breast cancer risk. A recent meta-analysis with prospective evidences did not support the positive association between IA and breast cancer risk. Thus, we in our meta-analysis study have tried to analyze this specific association.We searched all relevant articles from an English-language literature using Pubmed, Embase, and Cochrane databases, until December 10, 2016. All the statistical analyses were performed on case-control studies, using Review Manager Software 5.3 (Cochrane Collaboration, Oxford, UK).Our meta-analysis results based on 25 studies, including 5 studies with Chinese patients, indicated that there was no association of IA with breast cancer (OR = 1.08, 95% CI 0.98-1.19, P = .1). However, significant heterogeneity was observed, and thus further subgroup analyses were conducted. The combined OR of subjects with only 1-time IA was 1.03, 95% CI 0.90 to 1.18, P = .63, while for subjects with 2 or more IAs, it was 1.06, 95% CI 0.86 to 1.30, P = .58. In addition, the ORs of subjects, with 1st IA age either less than 30 or older than 30, were 1.05, 95% CI 0.88 to 1.26, P = .59, and 1.18, 95% CI 0.93 to 1.49, P = .17, respectively. These observations indicated that number of IAs and the age of 1st IA were not associated with breast cancer risk. Due to lack of dose-response relationships, it is difficult to say if number of IAs contributed into statistical heterogeneity. But after subgroup analysis, the age at the 1st IA appeared to impact the statistical heterogeneity. The different reproductive history appears to account for the high heterogeneity among individual studies. Also analysis of nulliparous women showed no significant difference in the association of IA and breast cancer (OR = 1.02, 95% CI 0.86-1.21, P = .85). However, parous women had higher IA rate in case group than control group (OR = 1.11, 95% CI 1.02-1.20, P = .01). Ethnicities might also result in high heterogeneity; thus, we conducted subgroup analyses on Chinese subjects, importantly, with 5 studies having Chinese patients, and did not observe any difference in the incidence of IA and its association with breast cancer between case and control groups (OR = 1.05, 95% CI 0.97-1.13, P = .21).After subgroup analysis, our study showed that IA might increase the risk of breast cancer in parous women, but in the nulliparous, IA was not significantly associated with an increased risk of breast cancer.

Screening methods (clinical breast examination and mammography) to detect breast cancer in women aged 40-49 years

Objective:

The aim of this study is to detect breast cancer rate, nodal status, tumor size, and associated risk factors using clinical breast examination (CBE) and mammography as screening tools in women aged 40–49 years.

Materials and Methods:

A total of 500 women were screened in a time period of 2 years, between the ages of 40–49 years for breast cancer. Screening tools used were CBE and mammography. Clinical history and risk factors related to breast cancer were recorded. CBE was performed to detect any breast pathology followed by mammographic screening. Breast Imaging Reporting and Data System (BI-RADS) mammographic density categories were used for reporting breast imaging on mammography. For women with dense breasts or an inconclusive mammography report, ultrasonography was performed to assess the lesion/s. Suspicious lesion was subjected to fine-needle aspiration cytology or an open surgical biopsy for a confirmatory diagnosis. Women with history of breast cancer were excluded from the study.

Results:

CBE was normal in almost 90% of the women. Screening mammography revealed Breast Imaging Reporting and Data System (BI-RADS) I and BI-RADS II in 58.4% and 34.6% of women, respectively. Only 7% of women belonged to BI-RADS III and none in BI-RADS IV category.

Conclusion:

The study findings are in agreement with the recommendations of the World Health Organization, US preventive task force and UK guidelines that recommend screening mammography in women starting at 50 years.

Screening for breast cancer

This review will give a general overview of the impact of breast cancer, as well as breast cancer risk factors, identification of high-risk groups, screening modalities, and guidelines for screening average-risk and high-risk individuals, including a case discussion of the primary care provider's approach to screening.

Grand multiparity and reproductive cancer in the Jerusalem Perinatal Study Cohort

OBJECTIVES

Grand multiparity is associated with reduced mortality from reproductive cancers. We aimed to separate the components of mortality, by measuring incidence of and survival after reproductive cancer onset in grand multiparous compared to other parous women.

STUDY DESIGN

We linked data from the population-based Jerusalem Perinatal Study Cohort, which included women aged 13-55 who delivered 1964-1976, with Israel's National Cancer Registry. We compared breast and gynecologic cancer risk and all-cause survival following a cancer diagnosis, among grand multiparae (GMPs = parity 5+, n = 8,246) versus women with parity 1-4 (n = 19,703), adjusting for reproductive and demographic variables.

RESULTS

Grand multiparae were at significantly lower risk of breast cancer than others (adjusted hazard ratio (HRadj) = 0.62, 95 % confidence interval (CI) 0.54-0.71), after controlling for age at first birth, education, and other covariates. This reduction was greater among GMPs whose first birth occurred after age 30 (p-interaction = 0.0001) and for cancer occurring before age 50 years (p = 0.002). In contrast, GMPs were at greater risk of death than women with parity <5, following a breast cancer diagnosis (HRadj = 1.69, CI 1.39-2.1). Ovarian, uterine, and cervical cancer incidence did not differ between the groups, but survival was reduced for GMPs with uterine cancer (HRadj = 2.48, CI 1.22-5.03).

CONCLUSION

Reduced reproductive cancer mortality reported among GMPs masks two opposing phenomena: decreased breast cancer risk and poorer survival after breast and uterine cancers. The latter unfavorable outcome suggests that tumors in GMPs may be particularly aggressive, having perhaps escaped protective mechanisms conferred by parity. This finding calls for heightened clinical attention in this group.

Breastfeeding and maternal health outcomes: a systematic review and meta-analysis

AIM

To evaluate the effect of breastfeeding on long-term (breast carcinoma, ovarian carcinoma, osteoporosis and type 2 diabetes mellitus) and short-term (lactational amenorrhoea, postpartum depression, postpartum weight change) maternal health outcomes.

METHODS

A systematic literature search was conducted in PubMed, Cochrane Library and CABI databases. Outcome estimates of odds ratios or relative risks or standardised mean differences were pooled. In cases of heterogeneity, subgroup analysis and meta-regression were explored.

RESULTS

Breastfeeding >12 months was associated with reduced risk of breast and ovarian carcinoma by 26% and 37%, respectively. No conclusive evidence of an association between breastfeeding and bone mineral density was found. Breastfeeding was associated with 32% lower risk of type 2 diabetes. Exclusive breastfeeding and predominant breastfeeding were associated with longer duration of amenorrhoea. Shorter duration of breastfeeding was associated with higher risk of postpartum depression. Evidence suggesting an association of breastfeeding with postpartum weight change was lacking.

CONCLUSION

This review supports the hypothesis that breastfeeding is protective against breast and ovarian carcinoma, and exclusive breastfeeding and predominant breastfeeding increase the duration of lactational amenorrhoea. There is evidence that breastfeeding reduces the risk of type 2 diabetes. However, an association between breastfeeding and bone mineral density or maternal depression or postpartum weight change was not evident.

Exposure to Bovine Leukemia Virus Is Associated with Breast Cancer: A Case-Control Study

BACKGROUND

Age, reproductive history, hormones, genetics, and lifestyle are known risk factors for breast cancer, but the agents that initiate cellular changes from normal to malignant are not understood. We previously detected bovine leukemia virus (BLV), a common oncogenic virus of cattle, in the breast epithelium of humans. The objective of this study was to determine whether the presence of BLV DNA in human mammary epithelium is associated with breast cancer.

METHODS

This was a case-control study of archival formalin fixed paraffin embedded breast tissues from 239 donors, received 2002-2008 from the Cooperative Human Tissue Network. Case definition as breast cancer versus normal (women with no history of breast cancer) was established through medical records and examination of tissues by an anatomical pathologist. Breast exposure to BLV was determined by in situ-PCR detection of a biomarker, BLV DNA, localized within mammary epithelium.

RESULTS

The frequency of BLV DNA in mammary epithelium from women with breast cancer (59%) was significantly higher than in normal controls (29%) (multiply- adjusted odds ratio = 3.07, confidence interval = 1.66-5.69, p = .0004, attributable risk = 37%). In women with premalignant breast changes the frequency of BLV DNA was intermediate (38%) between that of women with breast cancer and normal controls (p for trend < .001).

CONCLUSIONS

Among the specimens in this study, the presence of amplified BLV DNA was significantly associated with breast cancer. The odds ratio magnitude was comparable to those of well-established breast cancer risk factors related to reproductive history, hormones, and lifestyle and was exceeded only by risk factors related to genetics (familial breast cancer), high dose ionizing radiation, and age. These findings have the potential for primary and secondary prevention of breast cancer.

The human breast and the ancestral reproductive cycle : A preliminary inquiry into breast cancer etiology

This paper, using modern Darwinian theory, proposes an explanation for the increasingly high incidence of breast cancer found among pre-and post-menopausal women living today in westernized countries. A number of factors have been said to be responsible: genetic inheritance (BRCA-1), diet (specifically the increased consumption of dietary fat), exposure to carcinogenic agents, lifetime menstrual activity, and reproductive factors. The primary aim of this paper is to demonstrate the value of a perspective based on Darwinian theory. In this paper, Darwinian theory is used to explore the possibility that the increased incidence of breast cancer is due primarily to the failure to complete in a timely manner the reproductive developmental cycle, beginning at menarche and continuing through a series of pregnancies and lactation. On the basis of comparative data, we assume that most women in ancestral populations began having children before age 20 or so and tended to remain either pregnant or nursing for most of their adult lives. If a woman did not have a child by age 25 or so, she probably would never have one. Therefore, selection would probably not have acted against deleterious traits, such as cancer, that appeared after that age, just as it does not act against such traits in old age.

Risk factors of breast cancer: a systematic review and meta-analysis

The etiology of breast cancer might be explained by 2 mechanisms, namely, differentiation and proliferation of breast epithelial cells mediated by hormonal factors. We performed a systematic review and meta-analysis to update effects of risk factors for both mechanisms. MEDLINE and EMBASE were searched up to January 2011. Studies that assessed association between oral contraceptives (OC), hormonal replacement therapy (HRT), diabetes mellitus (DM), or breastfeeding and breast cancer were eligible. Relative risks with their confidence intervals (CIs) were extracted. A random-effects method was applied for pooling the effect size. The pooled odds ratios of OC, HRT, and DM were 1.10 (95% CI = 1.03-1.18), 1.23 (95% CI = 1.21-1.25), and 1.14 (95% CI = 1.09-1.19), respectively, whereas the pooled odds ratio of ever-breastfeeding was 0.72 (95% CI = 0.58-0.89). Our study suggests that OC, HRT, and DM might increase risks, whereas breastfeeding might lower risks of breast cancer.

Being breastfed in infancy and adult breast cancer risk among Japanese women

OBJECTIVE

Being breastfed in infancy has been hypothesized to influence subsequent breast cancer risk. In a hospital-based case-control study, we investigated the relationship between having been breastfed and breast cancer risk, both overall and separately among female subjects with different birth years.

METHODS

The study subjects included 571 cases and 2,155 controls admitted to a single hospital in Miyagi Prefecture, Japan, between 1997 and 2005. History of having been breastfed was assessed with a self-administered questionnaire. Odds ratios (ORs) and 95% confidence interval (CI) were estimated using logistic regression.

RESULTS

After adjustment for known risk factors, no association for having been breastfed was observed overall (OR = 1.20; 95% CI: 0.82-1.76). Analysis stratified according to birth year (<1950, ≥1950) demonstrated heterogeneity in the association for having been breastfed between the two birth-year groups (p for interaction = 0.0006); having been breastfed was significantly associated with a decreased risk among subjects who were born before 1950 (OR = 0.59; 95% CI: 0.35-0.99), whereas no such risk reduction was observed for subjects born after 1950 (OR = 1.60; 95% CI: 0.88-2.90).

CONCLUSION

Although having been breastfed is not related to overall risk, birth year may modify the association between having been breastfed in infancy and breast cancer risk. In Japan, sociodemographic changes have occurred since the end of World War II. The use of standard formula supplement began to spread around 1950. The difference of breast cancer risk between birth-year groups may be attributable to these environmental changes.

A review of body size and breast cancer risk in Hispanic and African American women

Obesity is an epidemic in the United States, especially among Hispanics and African Americans. Studies of obesity and breast cancer risk have been conducted primarily in non-Hispanic whites. There have been few studies of the association between body mass index (BMI) or weight gain and the risk of breast cancer in minorities, and the results have been inconsistent. Because most studies are conducted primarily in non-Hispanic whites, the etiology of breast cancer in minorities is not well understood. The authors of the current report reviewed the literature on the association between obesity, weight, and weight gain and breast cancer in minorities using a combination of the Medical Subject Heading (MeSH) terms "obesity," "body mass index," "weight," "weight gain," "Hispanic," and "African American." Only publications in English and with both risk estimates and 95% confidence intervals were considered. Forty-five studies of body size and breast cancer risk in non-Hispanic whites were identified. After an exhaustive search of the literature, only 3 studies of body size and breast cancer were conducted in Hispanic women were identified, and only 8 such studies in African American women were identified. The results were inconsistent in both race/ethnicity groups, with studies reporting positive, inverse, and null results. Thus, as obesity rates among Hispanics and African Americans continue to rise, there is an urgent need to identify the roles that both obesity and adult weight gain play in the development of breast cancer in these minorities. Additional studies are needed to provide more understanding of the etiology of this disease and to explain some of the disparities in incidence and mortality.

Abuse victimization and risk of breast cancer in the Black Women's Health Study [corrected]

Few studies have examined the relation between abuse victimization and breast cancer, and results have been inconclusive. Using data from 35,728 participants in the Black Women's Health Study, we conducted multivariable Cox regression to estimate incidence rate ratios (IRRs) and 95% confidence intervals (CI) for the association of abuse across the life span (childhood, adolescence, and adulthood) with breast cancer. Incident breast cancer diagnoses were reported during 1995-2009, and abuse histories were reported in 2005. No associations were found between abuse victimization in either childhood or adolescence and breast cancer. We found a weak positive association between abuse in adulthood and breast cancer (IRR = 1.18, 95% CI = 1.03-1.34). IRRs for physical abuse only, sexual abuse only, and both physical and sexual abuse in adulthood, relative to no abuse, were 1.28 (95% CI = 1.09-1.49), 0.96 (95% CI = 0.76-1.20), and 1.22 (95% CI = 1.00-1.49), respectively. IRRs for low, intermediate, and high frequencies of physical abuse in adulthood, relative to no abuse, were 1.28 (95% CI = 1.07-1.52), 1.37 (95% CI = 1.04-1.79), and 1.24 (95% CI = 0.95-1.62), respectively. Our data suggest an increased risk of breast cancer among African-American women who reported physical abuse in adulthood, but there was little evidence of a dose-response relation. These results require confirmation in other studies.

Short and long-term risks to women who conceive through in vitro fertilization

There are a number of potential risks to women who conceive through in vitro fertilisation (IVF). Among these, ovarian hyperstimulation syndrome and multiple pregnancies are the most serious. Other potential risks include increased levels of anxiety and depression, ovarian torsion, ectopic pregnancy, pre-eclampsia, placenta praevia, placental separation and increased risk of cesarean section. The association between assisted conception and long-term risk of cancer is debatable. The objective of this review is to critically evaluate the current evidence for potential risks to women who conceive through IVF. To assess the relative risk for any condition, a number of factors need to be taken into account including the method used in identifying the study and control group, the women's characteristics and the number of women included in the study. Many conditions such as ectopic pregnancy and pre-eclampsia appear to be commoner in assisted conception than in spontaneous pregnancy. Nevertheless, the increased risk of these conditions is probably related to the woman's subfertility status and/or increased incidence of multiple pregnancy. Currently, all efforts should concentrate on reduction of multiple births from IVF by restricting the number of transferred embryos.

Health effects of breast feeding for mothers: a critical review

Lactation results in a number of physiological adaptations which exert direct effects on maternal health, some of which may confer both short and long term advantages for breast feeding mothers. Breast feeding in the early postpartum period promotes a more rapid return of the uterus to its prepregnant state through the actions of oxytocin. Breast feeding may also lead to a more rapid return to prepregnancy weight. Among studies that had good data on duration and intensity of lactation, the majority show a significant association between lactation and weight loss. However, there is no evidence that lactation prevents obesity. Lactation also affects glucose and lipid metabolism. The long term effects of these adaptations are unknown but may have implications for preventing subsequent development of diabetes and heart disease. Lactation delays the return of ovulation and significantly reduces fertility during the period of lactational amenorrhoea. This process is linked with feeding patterns and may therefore be affected by practices such as scheduled feedings and the timing of introduction of complementary foods. While the evidence from epidemiologic studies is mixed, several large studies have shown that extended lactation is associated with reduced risk of premenopausal breast, ovarian and endometrial cancers. Although bone mineralization declines during lactation, repletion takes place after weaning. As a result, breast feeding does not appear to cause long term depletion of bone nor does it increase risk of osteoporosis. Many of the physiological effects of lactation are dependent on the stimulation of the hypothalamic-pituitary axis and milk removal and thus may vary with infant feeding practices. Well controlled studies are needed that include detailed information regarding infant feeding practices in addition to the total duration of any breast feeding. Future feeding recommendations should reflect careful consideration of how such practices affect both infant and maternal health.

Estimates of overdiagnosis of invasive breast cancer associated with screening mammography

PURPOSE

To estimate the extent of overdiagnosis of invasive breast cancer associated with screening in New South Wales, Australia, a population with a well-established mammography screening program which has achieved full geographic coverage.

METHODS

We calculated overdiagnosis as the observed annual incidence of invasive breast cancer in NSW in 1999-2001 (a screened population) minus the expected annual incidence in this population at the same time, as a percentage of the expected incidence. We estimated expected incidence without screening in 1999-2001 from the incidence of invasive breast cancer in: (1) women in unscreened age groups (interpolation method); and (2) women in all age groups prior to the implementation of screening (extrapolation method). We then adjusted these estimates for trends in major risk factors for breast cancer that may have coincided with the introduction of mammography screening: increasing obesity, use of hormone replacement therapy (HRT) and nulliparity. Finally, we adjusted for lead time to produce estimates of expected incidence in 1999-2001. These were compared with the observed incidence in 1999-2001 to calculate overdiagnosis of breast cancer associated with screening.

RESULTS

Overdiagnosis of invasive breast cancer among 50-69 year NSW women was estimated to be 42 and 30% using the interpolation and extrapolation methods, respectively.

CONCLUSION

Overdiagnosis of invasive breast cancer attributable to mammography screening appears to be substantial. Our estimates are similar to recent estimates from other screening programmes. Overdiagnosis merits greater attention in research and in clinical and public health policy making.

Through the Looking Glass at Early-Life Exposures and Breast Cancer Risk

The global increase in the proportion of women diagnosed with breast cancer, inadequate access to screening and high cost of treatment for breast cancer argue strongly for a greater focus on preventive strategies. But at what age is it appropriate to begin targeting preventive approaches? The recognized role of perinatal nutrition in neurologic development and the relation of maternal nutritional status to birthweight and subsequent risk of hypertension, diabetes, and cardiovascular disease identify pregnancy and early childhood as potential phases for prevention. This review examines indicators of hormonal and nutritional exposures in early life and breast cancer risk through the lens of the life course paradigm integrated with maternal and child health research and methodology. Compared to women who were normal birthweight (2500-3999 g), women who weighed>or=4,000 g at birth have a 20 percent to 5-fold increased risk of premenopausal breast cancer. Women born preterm and likely to be small- or large-for-date also have an increased risk. Birth length is directly associated with risk and has a larger magnitude of effect than birthweight. Prior preeclamptics and their daughters have a lower risk of breast cancer than comparable normotensives. An association between infant feeding practices and breast cancer is unclear without improved exposure assessment and analysis. Rapid childhood and pubertal linear growth increases breast cancer risk, while greater body fat over the same periods reduces risk. Growth data thus far have not been calculated in Z-scores from reference growth curves for comparison across studies. Events and secular trends influencing birth cohorts may not be adequately addressed, thereby limiting the interpretation and implications of the findings. Research in nonhuman primates may help uncover underlying mechanisms.

Exposure to breast milk in infancy and risk of breast cancer

Early life exposures, such as being breastfed in infancy, may influence the risk of breast cancer in adulthood. We evaluated the risk of breast cancer in relation to ever having been breastfed in infancy among 9,442 women who participated in a population-based, case-control study. Cases were identified through cancer registries in three states (Massachusetts, New Hampshire, and Wisconsin); controls were identified through statewide drivers' license lists or medicare lists. Data on known and suspected risk factors were obtained through telephone interview. We used unconditional logistic regression to assess the relation of breast cancer with ever having been breastfed and with breastfeeding duration (available for only 19% of breastfed women) in premenopausal women (1,986 cases and 1,760 controls) and postmenopausal women (2,600 cases and 2,493 controls). We found no evidence that ever having been breastfed in infancy was associated with breast cancer risk in either premenopausal women (odds ratio [OR] = 0.96; 95% confidence interval [CI] = 0.83-1.10) or postmenopausal women (OR = 0.98; 95% CI = 0.87-1.10). The association did not differ according to breast cancer stage, mother's history of breast cancer, or any other reproductive factor assessed. Likewise, we found no association between breastfeeding duration and risk of breast cancer. Our results did not support the hypothesis that exposure to breast milk in infancy influences the risk of adult breast cancer.

Do placental genes affect maternal breast cancer? Association between offspring's CGB5 and CSH1 gene variants and maternal breast cancer risk

The protective effect of full-term pregnancy against breast cancer is thought to be induced by two placental hormones: human chorionic gonadotropin and human chorionic somatotropin hormone (CSH) produced by the placental trophoblastic cells. We hypothesized that variants in placental genes encoding these hormones may alter maternal breast cancer risk subsequent to pregnancy. We conducted a case-control study to examine the association between polymorphisms in a woman's placental (i.e., her offspring's) homologous chorionic gonadotrophin beta5 (CGB5) and CSH1 genes and her post-pregnancy breast cancer risk. A total of 293 breast cancer cases and 240 controls with at least one offspring with available DNA were selected from the New York site of the Breast Cancer Family Registry. Three single nucleotide polymorphisms (SNP) in CGB5 and CSH1 genes were genotyped for 844 offspring of the cases and controls. Overall, maternal breast cancer risk did not significantly differ by the offspring's carrier status of the three SNPs. Among women with an earlier age at childbirth (younger than the median age of 26 years), those with a child carrying the variant C allele of CGB5 rs726002 SNP had an elevated breast cancer risk [odds ratio (OR), 2.09; 95% confidence interval (95% CI), 1.17-3.73]. Among women with a later age at childbirth, breast cancer risk did not differ by offspring's carrier status of CGB5 rs726002 SNP (OR, 0.90; 95% CI, 0.53-1.51; P for interaction=0.04). The findings suggest that placental CGB5 genotype may be predictive of maternal post-pregnancy breast cancer risk among women who give birth early in life.

Effects of birth order and maternal age on breast cancer risk: modification by whether women had been breast-fed

BACKGROUND

Early life risk factors for breast cancer have been investigated in relation to hormonal, nutritional, infectious, and genetic hypotheses. Recent studies have also considered potential health effects associated with exposure to environmental contaminants in breastmilk.

METHODS

We analyzed data from a population-based case-control study of women living in Wisconsin. Cases (n = 2016) had an incident diagnosis of invasive breast cancer in 2002-2006 reported to the statewide tumor registry. Controls (n = 1960) of similar ages were randomly selected from driver's license lists. Risk-factor information was collected during structured telephone interviews. Odds ratios (ORs) and 95% confidence intervals (CIs) were estimated from multivariable logistic regression.

RESULTS

In multivariable models, maternal age and birth order were not associated with breast cancer risk in the full study population. The odds ratio for breast cancer risk associated with having been breast-fed in infancy was 0.83 (95% CI = 0.72-0.96). In analyses restricted to breast-fed women, maternal age associations with breast cancer were null (P = 0.2). Increasing maternal age was negatively associated with breast cancer risk among women who were not breast-fed; the odds ratio for breast cancer associated with each 5-year increase in maternal age was 0.90 (0.82-1.00). Higher birth order was inversely associated with breast cancer risk among breast-fed women (for women with 3 or more older siblings compared with first-born women, OR = 0.58 [CI = 0.39-0.86]) but not among nonbreast-fed women (1.13 [0.81-1.57]).

CONCLUSION

These findings suggest that early life risk factor associations for breast cancer may differ according to breast-feeding status in infancy.

Infant feeding and the incidence of endometrial cancer

Biological mechanisms could support both an inverse and a direct association between exposure to breast milk in infancy and the risk of cancer. Having been breast-fed has been investigated in relation to the risk of breast and other cancer sites, and conflicting results have been reported. The association between infant feeding and the risk of endometrial cancer has not been explored. From 1976 to 2004, we followed 74,757 cancer-free participants in the Nurses' Health Study who had not undergone hysterectomy. Information on infant feeding was self-reported by study participants. A total of 708 incident cases of endometrial cancer were diagnosed during follow-up. After adjusting for age, family history of endometrial cancer, birth weight, premature birth, and birth order, the incidence of endometrial cancer was not associated with ever having been breast-fed (hazards ratio, 0.94; 95% confidence interval, 0.79-1.11) or duration of having been breast-fed [hazards ratio (95% confidence interval): 1.11 (0.80-1.54), 0.84 (0.62-1.13), 1.02 (0.79-1.31), respectively, for < or =3, 4-8, and > or =9 months of having been breastfed; P for trend = 0.88]. There was no significant effect modification by menopausal status, anthropometric factors (somatotype at age 5 or 10 years, body mass index at age 18 years, or current body mass index), or by other early-life exposures (birth weight, premature birth or exposure to parental smoking in childhood). Additional adjustment for adulthood risk factors of endometrial cancer did not materially change the results. Having been breast-fed was not associated with the incidence of endometrial cancer in this cohort, but statistical power for analyses restricted to premenopausal women was limited.

Age at first birth and the risk of breast cancer in BRCA1 and BRCA2 mutation carriers

An early age at first full-term birth is associated with a reduction in the subsequent development of breast cancer among women in the general population. A similar effect has not yet been reported among women who carry an inherited BRCA1 or BRCA2 mutation. We conducted a matched case-control study on 1816 pairs of women with a BRCA1 (n = 1405) or BRCA2 (n = 411) mutation in an attempt to elucidate the relationship between age at first full-term pregnancy and the risk of developing breast cancer. Information about the age at first childbirth and other pregnancy-related variables was derived from a questionnaire administered to women during the course of genetic counselling. There was no difference in the mean age at first full-term birth in the cases and controls (24.9 years vs. 24.8 years; P = 0.81, respectively). Compared to women whose first child was born at or before 18 years of age, a later age at first full-term birth did not influence the risk of developing breast cancer (OR = 1.00 per year; 95% CI 0.98-1.03; P-trend = 0.67). Stratification by mutation status did not affect the results. These findings suggest that an early first full-term birth does not confer protection against breast cancer in BRCA mutation carriers. Nonetheless, BRCA mutation carriers opting for a prophylactic oophorectomy as a breast and/or ovarian cancer risk-reducing strategy should complete childbearing prior to age 40 when this prevention modality is most effective.

Increased breast cancer risk after radiotherapy for acne among women with skin cancer

BACKGROUND

Radiotherapy was commonly used to treat benign conditions, especially skin diseases, during the first half of the twentieth century. Previous studies have shown that radiotherapy for some of these conditions increases the risk of developing breast cancer. Although breast cancer associated with previous radiotherapy for acne has been reported, no statistically significant correlation has been established.

OBJECTIVE

The aim of this study was to determine whether radiotherapy for acne is a risk factor for subsequent development of breast cancer.

METHODS

A retrospective nested case-control study was conducted using the cohort of all patients referred for Mohs micrographic surgery to the senior author (R. G. B.) from 1978 to 2003. The case group consisted of 244 women who were skin cancer patients and who had received radiotherapy for acne. The control group consisted of 244 age-matched women skin cancer patients from the same records randomly selected within the initial Mohs micrographic surgery treatment year. Clinical data from both groups regarding cancer history and radiotherapy were extracted and statistically analyzed.

RESULTS

Women skin cancer patients who had received radiotherapy for acne have a prevalence of breast cancer of 15% compared with 6.6% in control women skin cancer patients, for an odds ratio (OR) of 2.5 (P = .0033; 95% confidence interval, 1.3-4.6). Increased prevalence is correlated with age at treatment younger than 20 years (age-adjusted OR, 2.9; age-adjusted P = .002), treatment sessions numbering 5 or more (age-adjusted OR, 3.5; age-adjusted P = .005), and treatment year occurring before 1950 (age-adjusted OR, 2.9; age-adjusted P = .00013).

LIMITATIONS

The data used are based primarily on patient history and physical examinations and are therefore limited by the accuracy of the patient and the caregiver.

CONCLUSION

Women with skin cancer exposed to previous radiotherapy for acne are significantly more likely to develop breast cancer than their age-matched controls with skin cancer. Therefore all women previously treated for acne with radiotherapy should be identified and closely monitored for subsequent breast cancer development.

Breast-feeding and cancer: the Boyd Orr cohort and a systematic review with meta-analysis

BACKGROUND

Having been breast-fed has been suggested to influence cancer risk in adulthood. We investigated associations between breast-feeding during infancy and adult cancer incidence and mortality in a cohort study and meta-analyses of published studies.

METHODS

The Boyd Orr cohort consisted of 4999 subjects who were originally surveyed in 1937-39, when they were 0-19 years of age. Cancer outcomes from 1948 through 2003 were available for 4379 (88%) subjects, and 3844 had complete data on all covariates. Associations of breast-feeding with cancer were investigated using proportional hazards models. We also identified 14 studies on infant feeding and cancer published from 1966 through July 2005, of which 10 could be combined with the Boyd Orr cohort results in a meta-analysis of breast cancer using random-effect models.

RESULTS

In the Boyd Orr cohort, ever having been breast-fed, compared with never having been breast-fed, was not associated with the incidence of all cancers (hazard ratio [HR] = 1.07, 95% confidence interval [CI] = 0.89 to 1.28) or of any individual cancer type examined (prostate HR = 1.43, 95% CI = 0.58 to 3.52; breast HR = 1.62, 95% CI = 0.89 to 2.94; colorectal HR = 0.86, 95% CI = 0.45 to 1.63; gastric HR = 1.22, 95% CI = 0.47 to 3.15). In the meta-analysis, there was also no association between breast-feeding and breast cancer (regardless of menopausal status) (relative risk [RR] = 0.94, 95% CI = 0.85 to 1.04). However, breast-fed women had a reduced risk of premenopausal breast cancer (RR = 0.88, 95% CI = 0.79 to 0.98) but not of postmenopausal breast cancer (RR = 1.00, 95% CI = 0.86 to 1.16).

CONCLUSION

Ever having been breast-fed was not associated with overall breast cancer risk, although the meta-analysis revealed a reduced risk of premenopausal breast cancer in women who had been breast-fed.

Prenatal and perinatal correlates of adult mammographic breast density

BACKGROUND

Adult mammographic percent density is one of the strongest known risk factors for breast cancer. In utero exposure to high levels of endogenous estrogens (or other pregnancy hormones) has been hypothesized to increase breast cancer risk in later life. We examined the hypothesis that those factors associated with higher levels of estrogen during pregnancy or shortly after birth are associated with higher mammographic breast density in adulthood.

METHODS

We analyzed data on 1,893 women from 360 families in the Minnesota Breast Cancer Family Study who had screening mammograms, risk factor data, over age 40, and no history of breast cancer. Prenatal and perinatal risk factor data were ascertained using a mailed questionnaire. Mammographic percent density and dense area were estimated from the mediolateral oblique view using Cumulus, a computer-assisted thresholding program. Linear mixed effects models incorporating familial correlation were used to assess the association of risk factors with percent density, adjusting for age, weight, and other breast cancer risk factors, all at time of mammography.

RESULTS

The mean age at mammography was 60.4 years (range, 40-91 years), and 76% were postmenopausal. Among postmenopausal women, there was a positive association of birthweight with percent density (P trend <0.01), with an adjusted mean percent density of 17.1% for <2.95 kg versus 21.0% for > or = 3.75 kg. There were suggestive positive associations with gestational age (mean percent density of 16.7% for preterm birth, 20.2% for term birth, and 23.0% for late birth; P trend = 0.07), maternal eclampsia/preeclampsia (mean percent density of 19.9% for no and 14.6% for yes; P = 0.16), and being breast-fed as an infant (mean percent density of 18.2% for never and 20.0% for ever; P = 0.08). There was no association of percent density with maternal age, birth order, maternal use of alcohol or cigarettes, or neonatal jaundice. Except for being breast-fed, these associations showed similar but attenuated trends among premenopausal women, although none were statistically significant. The results for dense area paralleled the percent density results. The associations of gestational age and being breast-fed as an infant with percent density attenuated when included in the same model as birthweight.

CONCLUSIONS

Birthweight was positively associated with mammographic breast density and dense area among postmenopausal women and more weakly among premenopausal women, suggesting that it may be a marker of this early life exposure. These results offer some support to the hypothesis that pregnancy estrogens or other pregnancy changes may play a role in breast cancer etiology, and suggest that these factors may act in part through long-term effects on breast density.

Analysis of menstrual, reproductive, and life-style factors for breast cancer risk in Turkish women: a case-control study

The aim of this study was to investigate the association between menstrual, reproductive, and life-style factors and breast cancer in Turkish women. In a hospital-based case-control study in Ankara, 622 patients with histologically confirmed breast cancer were compared with 622 age-matched controls, admitted to the same hospital for acute and non-neoplastic diseases. Unconditional logistic regression was used to estimate odds ratios (ORs) and 95% confidence intervals (CI) related to risk factors. Overall, menopausal status and age at menopause were found to be significantly associated with breast cancer. Having a full-term pregnancy and early age at first birth were associated with decreased breast cancer risk (OR = 0.45, 95% CI = 0.30-0.66; OR = 0.34, 95% CI = 0.22-0.53, respectively). Postmenopausal women with lactation longer than 48 mo had reduced risk of breast cancer (OR = 0.36, 95% CI = 0.14-0.93). In conclusion, decreased parity, late age at first birth, early menopause, and shorter duration of lactation were the most important determinants of breast cancer risk in Turkish women.

Breast cancer and abortion: collaborative reanalysis of data from 53 epidemiological studies, including 83?000 women with breast cancer from 16 countries

BACKGROUND

The Collaborative Group on Hormonal Factors in Breast Cancer has brought together the worldwide epidemiological evidence on the possible relation between breast cancer and previous spontaneous and induced abortions.

METHODS

Data on individual women from 53 studies undertaken in 16 countries with liberal abortion laws were checked and analysed centrally. Relative risks of breast cancer--comparing the effects of having had a pregnancy that ended as an abortion with those of never having had that pregnancy--were calculated, stratified by study, age at diagnosis, parity, and age at first birth. Because the extent of under-reporting of past induced abortions might be influenced by whether or not women had been diagnosed with breast cancer, results of the studies--including a total of 44000 women with breast cancer--that used prospective information on abortion (ie, information that had been recorded before the diagnosis of breast cancer) were considered separately from results of the studies--including 39000 women with the disease--that used retrospective information (recorded after the diagnosis of breast cancer).

FINDINGS

The overall relative risk of breast cancer, comparing women with a prospective record of having had one or more pregnancies that ended as a spontaneous abortion versus women with no such record, was 0.98 (95% CI 0.92-1.04, p=0.5). The corresponding relative risk for induced abortion was 0.93 (0.89-0.96, p=0.0002). Among women with a prospective record of having had a spontaneous or an induced abortion, the risk of breast cancer did not differ significantly according to the number or timing of either type of abortion. Published results on induced abortion from the few studies with prospectively recorded information that were not available for inclusion here are consistent with these findings. Overall results for induced abortion differed substantially between studies with prospective and those with retrospective information on abortion (test for heterogeneity between relative risks: chi2(1) =33.1, p<0.0001).

INTERPRETATION

Pregnancies that end as a spontaneous or induced abortion do not increase a woman's risk of developing breast cancer. Collectively, the studies of breast cancer with retrospective recording of induced abortion yielded misleading results, possibly because women who had developed breast cancer were, on average, more likely than other women to disclose previous induced abortions.

Breastfeeding and breast cancer: a case-control study in Southern Brazil

To investigate the relationship between breastfeeding and breast cancer in Southern Brazil, a case-control design was employed, with two age-matched control groups. A total of 250 cases of breast cancer were identified in women from 20 to 60 years of age, with 1,020 hospital and community controls. The main study variables were occurrence of breastfeeding and duration of breastfeeding. A multivariate conditional logistic regression analysis was employed. According to the results, breastfeeding did not have a protective effect against breast cancer. The odds ratio (OR) for women who breastfed was 0.9 (95% CI: 0.8-1.2) compared to women who did not breastfeed. For women who breastfed for six months or less, the OR was 1.0 (95% CI: 0.6-1.8). In pre-menopausal women who breastfed for more than 25 months, the OR was 0.95 (95% CI: 0.5-3.5), and in post-menopausal women OR was 1.27 (95% CI: 0.5-3.1), compared to women who had not breastfeed.

Null association between pregnancy termination and breast cancer in a registry-based study of parous women

Studies suggesting a positive association between pregnancy termination and breast cancer risk have often been of retrospective case-control design, so subject to selection and recall biases. We undertook a registry-based analysis with minimal selection bias and prospective record-based ascertainment of terminations. The source population comprised Massachusetts women with a record of giving birth between 1987 and 1999 in the Massachusetts Vital Statistics Registry. Primary breast cancer cases were 25-55 years old at diagnosis between 1988 and 2000 and had a record of the diagnosis in the Massachusetts Cancer Registry. We matched 3 controls to each case on maternal age, year of giving birth and birth facility. Information on terminations (induced and spontaneous) before the birth of record, the matched factors and potential confounders were collected from the birth certificate. After adjustment for the matched factors, age, parity and maternal and paternal education, the odds ratio associating any termination history with breast cancer risk equaled 0.91 (95% CI = 0.79-1.05). The marginally protective adjusted odds ratio largely derived from a protective effect among women with parity equaled to 1 (OR for any termination = 0.68; 95% CI = 0.45-1.03), suggesting a protective effect of terminated pregnancy among women with one live birth.

Rating the risk factors for breast cancer

OBJECTIVE

To update and summarize evidence of risk factors for breast cancer.

SUMMARY BACKGROUND DATA

Women who are at high risk for breast cancer have a variety of options available to them, including watchful waiting, prophylactic surgery, and chemoprevention. It is increasingly important to accurately assess a patient's risk profile to ensure that the cost/benefit ratio of the selected treatment is favorable.

METHODS

Estimates of relative risk for documented risk factors were obtained from seminal papers identified in previous reviews. These estimates were updated where appropriate with data from more recent reports using large sample sizes or presenting meta-analyses of previous studies. These reports were identified from a review of the Medline database from 1992 to 2002.

RESULTS

Risk factors that have received a great deal of publicity (hormone use, alcohol consumption, obesity, nulliparity) present a relatively modest relative risk for breast cancer (<2). Factors associated with a prior history of neoplastic disease or atypical hyperplasia and factors associated with a genetic predisposition significantly affect the risk of breast cancer, with relative risks ranging from 3 (for some cases of positive family history) to 200 (for premenopausal women positive for a BRCA mutation).

CONCLUSIONS

More precise tools, based on techniques of molecular biology such as microarray analysis, will be needed to assess individual risk for breast cancer.

Breast cancer risk assessment models: applicability to African-American women

BACKGROUND

Mortality rates are higher among African-American women with breast cancer than they are among white women. This population subset can benefit from available risk reduction strategies. Optimal public health gains from chemoprevention strategies depend on the ability to assess accurately the risk for the individual. However, it is not known if existing breast cancer prediction models are accurate predictors of the disease among African-American women.

METHODS

Literature was reviewed for breast cancer risk prediction models and their validation studies. Reported data were also reviewed regarding the strength of established breast cancer risk factors for African-American women.

RESULTS

The two currently accepted breast cancer risk assessment models, the Gail Model and the Claus Model, were designed primarily to provide risk assessments for white women. Neither model has been validated in African-American women. Reported data are inconsistent regarding the prevalence and strength of risk factors included in these models.

CONCLUSIONS

Efforts should be made to validate existing risk assessment models in African-American women and future research should be directed at the identification of more reliable risk assessment features.

Abortion history and breast cancer risk: results from the Shanghai Breast Cancer Study

Studies of the association between induced abortion and breast cancer risk have been inconsistent, perhaps due to underreporting of abortions. Induced abortion is a well-accepted family planning procedure in China, and women who have several induced abortions do not feel stigmatized. The authors used data from a population-based case-control study of breast cancer among women age 25-64 conducted between 1996 and 1998 in urban Shanghai to assess whether a history of and the number of induced abortions were related to breast cancer risk. In-person interviews were completed with 1,459 incident breast cancer cases ascertained through a population-based cancer registry, and 1,556 controls randomly selected from the general population in Shanghai (with respective response rates of 91% and 90%). After adjusting for confounding, there was no relation between ever having had an induced abortion and breast cancer (odds ratio [OR] = 0.9, 95% confidence interval [CI] 0.7-1.2). Women who had 3 or more induced abortions were not at increased risk of premenopausal breast cancer (OR = 0.9, 95% CI 0.6-1.4) or postmenopausal breast cancer (OR = 1.3, 95% CI 0.8-2.3). These results suggest that a history of several induced abortions has little influence on breast cancer risk in Chinese women.

Low pO2 and beta-estradiol induce VEGF in MCF-7 and MCF-7-5C cells: relationship to in vivo hypoxia

Previous work from this laboratory demonstrated that MCF-7 breast carcinoma cells grown in nude mice contained minimal hypoxia but that tamoxifen treatment of these tumors resulted in increased hypoxia (Evans S. et al., Cancer Research, 1997). These findings led to studies exploring the link between estrogen signaling and tumor oxygenation and determining the role of VEGF in this process. The stimulation of estrogen-dependent MCF-7 breast carcinoma cells in vitro with beta-estradiol resulted in a two-fold induction of VEGF mRNA and 1.3-2-fold increase in protein, similar to what was observed when these cells were exposed to 0. 1% oxygen. Furthermore, the two stimuli given together had an additive effect on (increasing) VEGF expression, suggesting that the combination of hypoxia and estrogen may be important in upregulating VEGF in some breast cancers. Estrogen-independent MCF-7-5C cells, developed by growing MCF-7 cells in long-term culture in estrogen-free media, were also studied. Using EF5, a fluorinated 2-nitroimidazole which localizes to hypoxic cells, MCF-7-5C tumors grown in nude mice were found to contain lower pO2 levels and more hypoxic regions than similarly grown MCF-7 tumors. We tested the hypothesis that this might be the result of defective expression of VEGF in MCF-7-5C cells in response to beta-estradiol and/or hypoxia. However, MCF-7-5C and MCF-7 cells showed a similar induction of VEGF in vitro in response to either beta-estradiol or hypoxia. Therefore, although these two cell lines grown as tumors have substantial differences in the presence and patterns of hypoxia, this could not be explained by a difference in VEGF induction.

Being breastfed in infancy and breast cancer incidence in adult life: results from the two nurses' health studies

Events during perinatal and early life may influence the incidence of breast cancer in adult life, and some case-control studies suggest that having been breastfed may reduce breast cancer risk. The authors studied this association among premenopausal and postmenopausal women by using data from the two Nurses' Health Studies, the Nurses' Health Study (using data from 1992 to 1996) and the Nurses' Health Study II (using data from 1991 to 1997). A history of being breastfed was self-reported by the study participants. During a total of 695,655 person-years, 1,073 cases of invasive breast cancer were diagnosed. The authors did not observe any important overall association between having been breastfed and the development of breast cancer later in life among premenopausal women (covariate-adjusted relative risk = 0.97, 95% confidence interval (CI): 0.78, 1.20) or postmenopausal women (covariate-adjusted relative risk = 1.12, 95% CI: 0.92, 1.37). No significant trend was observed with increasing duration of breastfeeding. The authors also used data on breastfeeding retrospectively collected from 2,103 mothers of participants of the two Nurses' Health Studies. With the mothers' reports, the covariate-adjusted odds ratio of breast cancer was 1.11 (95% CI: 0.88, 1.39) for women who were breastfed compared with those who were not. Data from these two large cohorts do not support the hypothesis that being breastfed confers protection against subsequent breast cancer.

Lactation reduces breast cancer risk in Shandong Province, China

Results from studies of western populations investigating lactation and breast cancer risk have been inconsistent. To examine this issue, the authors conducted a hospital-based case-control study in Shandong Province, China, in 1997-1999. A total of 404 cases and an equal number of controls were included. Detailed information regarding lactation, menstruation, and reproduction was collected through in-person interview. The authors found a significant inverse association between duration of lactation and breast cancer risk. For women who breastfed for more than 24 months per child, the odds ratio was 0.46 (95% confidence interval (CI): 0.27, 0.78) when compared with those who breastfed for 1-6 months per child. A significantly reduced risk of breast cancer was also found for those whose lifetime duration of lactation totaled 73-108 months (odds ratio = 0.47, 95% CI: 0.23, 0.95) and for those who breastfed for > or =109 months (odds ratio = 0.24, 95% CI: 0.11, 0.53). The test for trend was statistically significant for both mean duration of lactation per child (p = 0.02) and lifetime duration of lactation (p = 0.00). Further stratification by menopausal status resulted in the same conclusion. These data suggest that prolonged lactation reduces breast cancer risk.

Induced abortion and breast cancer risk

Results from case-control studies suggest that induced abortion may be associated with a small increase in risk of breast cancer. While risk estimates from cohort studies have generally not observed such an association, these studies have had limited information regarding abortion and possible confounding variables. Therefore, we conducted a study among a cohort of post-menopausal women from whom detailed information regarding pregnancy outcomes as well as risk factors for breast cancer had been collected. The study sample included 37,247 Iowa Women's Health Study participants, 55-64 years of age at baseline in 1986, who reported no history of breast, or other, cancer (except non-melanoma skin cancer), and for whom information regarding pregnancy outcomes (that is, live birth, stillbirth, spontaneous abortion, ectopic pregnancy or induced abortion) was available. We used linkage with records of the State Health Registry of Iowa, part of the National Cancer Institute's Surveillance, Epidemiology, and End Results (SEER) program, to estimate the incidence of breast cancer among cohort members through 1995. We calculated age-adjusted relative risks and 95% confidence intervals using Cox proportional hazards regression. Only 653 women (1.8%) reported an induced abortion. The age-adjusted relative risk of breast cancer among women with prior induced abortion compared with those without was 1.1 (95% CI = 0.8-1.6). Relative risks were higher among women whose age at first abortion was less than 20 or at least 30 years, for those whose abortion took place after their first birth or who never gave birth, and for those with early termination (0-2 months). These estimates varied from 1.3-1.7, but the confidence intervals around each were wide. Since most women in this cohort were beyond their reproductive years when abortion became legal in 1973, the low prevalence of induced abortion argues for a cautious interpretation.

Lactation and breast carcinoma risk in a South African population

BACKGROUND

A number of epidemiologic studies have reported a reduced risk of breast carcinoma among women who have lactated but others have not. The current study presents data regarding lactation and breast carcinoma risk from a hospital-based case-control study of black and colored South African women.

METHODS

Incident breast carcinoma cases treated between January 1994 and October 1997 (n = 446) at 2 major hospitals in Cape Town and hospital patients admitted for conditions unrelated to breast carcinoma (controls, n = 1471) were queried regarding the duration of breast-feeding each liveborn child and breast carcinoma risk factors. Multivariate logistic regression models were used to calculate odds ratios (ORs) for various categories of lactation compared with a reference category of never having breast-fed among women who had had at least one full term live birth.

RESULTS

Approximately 83% of cases and 85% of controls had ever breast-fed (OR = 0.9; 95% confidence interval [95% CI], 0.7-1.3). Among all subjects, the ORs for those who lactated for <3 years were near or at unity. Beyond 3 years, ORs extending up to >/=7 years were less than unity, but the 95% CIs included 1.0 (OR for duration of >/=7 years = 0.7; 95% CI, 0.4-1.3). ORs did not vary by menopausal status. Breast carcinoma risk was not found to be related to the duration of breast-feeding the first child, the number of children breast-fed, or the patient's age at first lactation.

CONCLUSIONS

The results of the current study suggest lactation has little or no protective effect on breast carcinoma risk.

Adolescent reproductive events and subsequent breast cancer risk

OBJECTIVES

This study investigated the relationship between reproductive events during adolescence and subsequent breast cancer risk.

METHODS

Logistic regression models used self-reported data from 862 case patients and 790 controls in the Carolina Breast Cancer Study.

RESULTS

Miscarriage, induced abortion, and full-term pregnancy before 20 years of age were not associated with breast cancer. Among premenopausal women, breast-feeding before 20 years of age was inversely associated with disease. Oral contraceptive use before 18 years of age was positively associated with disease risk among African American women only.

CONCLUSIONS

Pregnancy during adolescence does not appear to influence breast cancer risk, but breast-feeding may. A possible increased breast cancer risk among African American women who used oral contraceptives as adolescents warrants further study.

Preterm delivery and risk of breast cancer

To explore the risk of breast cancer in relation to the length of a pregnancy we tested whether a preterm delivery carries a higher risk of breast cancer than does a full-term delivery. Based on information from the Civil Registration System, and the National Birth Registry in Denmark, we established a population-based cohort of 474 156 women born since April 1935, with vital status and detailed parity information, including the gestational age of liveborn children and stillbirths. Information on spontaneous and induced abortions was obtained from the National Hospital Discharge Registry and the National Registry of Induced Abortions. Incident cases of breast cancer in the cohort (n = 1363) were identified through linkage with the Danish Cancer Registry. The period at risk started in 1978 and continued until a breast cancer diagnosis, death, emigration, or 31 December, 1992, whichever occurred first. After adjusting for attained age, parity, age at first birth and calendar period, we observed the following relative risks of breast cancer for different lengths of the pregnancy: < 29 gestational weeks = 2.11 (95% confidence interval 1.00-4.45); 29-31 weeks = 2.08 (1.20-3.60); 32-33 weeks = 1.12 (0.62-2.04); 34-35 weeks = 1.08 (0.71-1.66); 36-37 weeks = 1.04 (0.83-1.32); 38-39 weeks = 1.02 (0.89-1.17); 40 weeks = 1 (reference). Parous women who had a preterm delivery below 32 weeks gestation had a 1.72-fold (1.14-2.59) increased risk of breast cancer compared with other parous women. In conclusion, a preterm delivery of 32+ weeks gestation did not significantly increase a woman's risk of contracting breast cancer. Only for the very small group of women with preterm deliveries of less than 32 weeks gestation did we observe an increased risk.

The alleged association between induced abortion and risk of breast cancer: biology or bias?

The alleged association between induced abortion and breast cancer is one of the most controversial and important questions in women's health today. To help clinicians provide appropriate counseling, we reviewed both the primary data and review articles on this topic. We identified the studies and reviews by using Medline and the reference lists of articles and texts. We then used the U.S. Preventive Services Task Force rating system to evaluate the evidence. Many case-control studies have addressed this question, but their results have been inconsistent. Persistent problems in the case-control studies include selection of an appropriate control group, recall bias (under-reporting of induced abortion by controls), and confounding by other risk factors. Two recent, large cohort studies, which are less susceptible to bias, showed either protection or no effect on breast cancer risk from an induced abortion. At present, level II-2 evidence (cohort and case-control studies) supports a class B recommendation (fair evidence) that induced abortion does not increase a woman's risk of breast cancer later in life.

Exposure to breast milk in infancy and adult breast cancer risk

BACKGROUND

There is considerable interest in the possibility of an infectious etiology for human breast cancer. Although studies have shown that certain strains of mice transmit mammary tumor virus via breast milk, few epidemiologic studies have addressed this topic in humans.

METHODS

We evaluated the relationship between having been breast-fed as an infant and breast cancer risk among 8299 women who participated in a population-based, case-control study of breast cancer in women aged 50 years or more. Case women were identified through cancer registries in three states (Massachusetts, New Hampshire, and Wisconsin); control women were identified through statewide driver's license lists (age <65 years) or Medicare lists (ages 65-79 years). Information on epidemiologic risk factors was obtained through telephone interview. We used multiple logistic regression to assess having been breast-fed and maternal history of breast cancer in relation to breast cancer occurrence both in premenopausal women (205 case women; 220 control women) and in postmenopausal women (3803 case women; 4071 control women).

RESULTS

We found no evidence that having been breast-fed increased breast cancer risk in either premenopausal women (odds ratio [OR] = 0.65; 95% confidence interval [CI] = 0.41-1.04) or postmenopausal women (OR = 0.95; 95% CI = 0.85-1.07). In addition, breast cancer risk was not increased by having been breast-fed by a mother who later developed breast cancer.

CONCLUSION

Our results do not support the hypothesis that a transmissible agent in breast milk increases breast cancer risk. Because premenopausal women were not well represented in our study population, our findings with regard to this group may not be generalizable and should be viewed with caution.