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

A Meta-Analysis of Induced Abortion, Alcohol Consumption, and Smoking Triggering Breast Cancer Risk among Women from Developed and Least Developed Countries

BACKGROUND

The most prominent form of cancer in women is breast cancer, and modifiable lifestyle risk factors, including smoking, alcohol consumption, and induced abortion, can all contribute significantly to this disease.

OBJECTIVES

This study's primary purpose was to assess the prevalence of breast cancer among women in developed and developing countries and the association between three modifiable hazard factors (induced abortion, smoking behavior, and alcohol use) and breast cancer.

METHODS

This study performed a systematic literature database review up to September 21, 2021. We employed meta-analytic tools such as the random effects model, forest plot, and subgroup analysis to conduct the research. Additionally, we conducted a sensitivity analysis to assess the influence of outliers.

RESULTS

According to the random effects model, smoker women have a higher risk of developing breast cancer from different countries (OR = 1.46; 95% CI: 1.08-1.97). In the case of induced abortion, the pooled estimate (OR = 1.25; 95% CI: 1.01-1.53) indicated a significant link between abortion and breast cancer. Subgroup analysis revealed that smoking substantially influences breast cancer in developing and developed countries. Breast cancer was more common among women who smoked in developed countries than in developing nations.

CONCLUSION

The observed findings give sufficient support for the hypothesis that smoking and abortion have a significant influence on breast cancer in different nations. Health organizations should individually design comprehensive scientific plans to raise awareness about the risks of abortion and smoking in developed and developing countries.

Abortion and Breast Cancer: Case-Control Study

Aims and background

The aim of the present study was to examine if certain aspects of a woman's experience of abortion might be associated with the risk of breast cancer.

Methods and study design

The case-control study was conducted in Kragujevac (Serbia) during the period 2004–2005. The case group (191 women) consisted of patients with newly diagnosed first primary breast cancer, which was histologically confirmed. The control group (191 women), individually matched by age (± 2 years), hospital admittance and place of residence (rural/urban) to the respective cases, was selected from female patients admitted for other diseases. The analysis was restricted to parous women (168 cases and 171 controls).

Results

Breast cancer risk was reduced among women who had a history of any abortion (adjusted OR, 0.46; 95% CI, 0.24–0.88). The protective effect was found for both induced abortion (adjusted OR, 0.47; 95% CI, 0.25–0.90) and spontaneous abortion (adjusted OR, 0.31; 95% CI, 0.10–0.98). It seems that these associations did not depend on the number of abortions, age at first abortion, or gestational age at first aborted pregnancy.

Conclusions

Our study suggests that even short pregnancies ending in abortion add to the protection against 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.

The epidemiological profile of hysterectomy in rural Chinese women: a population-based study

OBJECTIVES

Hysterectomy is one of the most common surgical procedures performed on women in developed countries; however, little is known about the epidemiology of hysterectomy in low-income to middle-income regions. This study seeks to evaluate the prevalence of hysterectomy and its risk factors in rural China.

METHODS

Questionnaires were collected from 3328 female adults aged 25â€"69 years in rural Anyang, China, in 2009â€"2011. Hysterectomy status was ascertained by the gynaecologist at the time of cytological test. Univariate and multivariate regression analyses were performed to assess the risk factors for hysterectomy.

RESULTS

The overall prevalence of hysterectomy was 3.31% (110/3328). Women above the age of 40 years had a higher prevalence of prior hysterectomy, compared with those aged 25â€"39 years (5.01% vs 0.33%). Obesity was marginally related with a higher risk of hysterectomy (adjusted OR=1.59; 95% CI 0.99 to 2.56; body mass index (BMI) ≥28.0 vs 18.5 ≤ BMI <24.0). History of prior pregnancy loss conferred a greater risk for hysterectomy (adjusted OR=1.51; 95% CI 1.02 to 2.23). Of the 75 (68.18%, 75/110) cases who provided further information on hysterectomy, 84.00% (63/75) had undergone total abdominal hysterectomy and 70.67% (53/75) had received surgery for leiomyoma.

CONCLUSIONS

Rural Chinese women had a relatively low prevalence of hysterectomy, and the majority of reported hysterectomies were performed abdominally for leiomyoma. Hysterectomy prevalence differed significantly by age, BMI and history of pregnancy loss. This study expands the current understanding of the epidemiology of hysterectomy in lower resource areas.

Induced abortion and breast cancer: results from a population-based case control study in China

AIM

To determine whether induced abortion (IA) increases breast cancer (BC) risk.

MATERIALS AND METHODS

A population-based case-control study was performed from Dec, 2000 to November, 2004 in Shanghai, China, where IA could be verified through the family planning network and client medical records. Structured questionnaires were completed by 1,517 cases with primary invasive epithelial breast cancer and 1,573 controls frequency- matched to cases for age group. The information was supplemented and verified by the family planning records. Statistical analysis was conducted with SAS 9.0.

RESULTS

After adjusting for potential confounders, induced abortions were not found to be associated with breast cancer with OR=0.94 (95%CI= 0.79-1.11). Compared to parous women without induced abortion, parous women with 3 or more times induced abortion (OR=0.66, 95%CI=0.46 to 0.95) and women with 3 or more times induced abortion after the first live birth (OR=0.66, 95%CI =0.45 to 0.97) showed a lower risk of breast cancer, after adjustment for age, level of education, annual income per capita, age at menarche, menopause, parity times, spontaneous abortion, age at first live birth, breast-feeding, oral contraceptives, hormones drug, breast disease, BMI, drinking alcohol, drinking tea, taking vitamin/calcium tablet, physical activity, vocation, history of breast cancer, eating the bean.

CONCLUSIONS

The results suggest that a history of induced abortions may not increase the risk of breast cancer.

Associations of reproductive time events and intervals with breast cancer risk: a report from the Shanghai Breast Cancer Study

While there is clear evidence for an association between later age at first live birth and increased breast cancer risk, associations with the timing of other reproductive events are less clear. As breast tissues undergo major structural and cellular changes during pregnancy, we examined associations between reproductive time events and intervals with breast cancer risk among parous women from the population-based Shanghai Breast Cancer Study (SBCS). Unconditional logistic regression was used to evaluate associations with breast cancer risk for 3,269 cases and 3,341 controls. In addition to later age at first live birth, later ages at first pregnancy and last pregnancy were significantly associated with increased breast cancer risk (p-trend = 0.002, 0.015, 0.008, respectively); longer intervals from menarche to first or last live birth were also associated with increased risk (p-trend < 0.001, =0.018, respectively). Analyses stratified by menopausal status and estrogen receptor (ER)/progesterone receptor (PR) status revealed that associations for later age at first pregnancy or live birth and longer intervals from menarche to first or last live birth occurred among premenopausal women and ER+/PR+ breast cancers, whereas the association for later age at last pregnancy occurred among postmenopausal women and women with ER+/PR- or ER-/PR+ breast cancers. Because of the high correlation with other reproductive variables, models did not include adjustment for age at first live birth; when included, the significance of all associations was attenuated. These findings suggest that while reproductive time events and intervals play an important role in breast cancer etiology, contributions may differ by menopausal status and hormone receptor status of breast cancers.

Risk factors for breast cancer among Chinese women: a 10-year nationwide multicenter cross-sectional study

Background

The characteristics of established risk factors for breast cancer may vary among countries. A better understanding of local characteristics of risk factors may help in devising effective prevention strategies for breast cancer.

Methods

Information on exposures to risk factors was collected from the medical charts of 4211 women with breast cancer diagnosed during 1999–2008. The distributions of these exposures among regions, and by menopausal status and birth period, were compared with the χ² test. Crude associations between the selected factors and breast cancer were estimated using the cases in the present study and a representative control population, which was selected from qualified published studies.

Results

As compared with cases from less developed regions, those from more developed regions were significantly more likely to be nulliparous, had fewer childbirths (P < 0.05), and were less likely to have breastfed (P = 0.08). As compared with premenopausal cases, postmenopausal cases were more likely to be overweight and to have breastfed and had more childbirths (P < 0.05). The number of live births and rate of breastfeeding decreased in relation to birth period (P for trends <0.001). Overweight, late menopause, and family history of breast cancer were significantly associated with breast cancer among Chinese women.

Conclusions

Breast cancer incidence was associated with nulliparity and history of breastfeeding. Population attributable risks should be assessed, especially for more developed areas and young women. The effects of body mass index, age at menopause, and family history of breast cancer should be given priority during assessment of breast cancer risk among Chinese women.

Association of overweight and obesity with breast cancer in India

Background:

In women, cancer of the breast is one of the most common incident cancer and cause of death from cancer. Anthropometric factors of weight, height, and body mass index (BMI) have been associated with breast cancer risk.

Objectives:

To study the association of overweight and obesity with breast cancer in India.

Materials and Methods:

A hospital-based matched case-control study was conducted. Three hundred and twenty newly diagnosed breast cancer patients and three hundred and twenty normal healthy individuals constituted the study population. The subjects in the control group were matched individually with the patients for their age ±2 years and socioeconomic status. Anthropometric measurements of weight and height were recorded utilizing the standard equipments and methodology. The paired ‘t’ test and univariate logistic regression analysis were carried out.

Results:

It was observed that the patients had a statistically higher mean weight, body mass index, and mid upper arm circumference as compared to the controls. It was observed that the risk of breast cancer increased with increasing levels of BMI. Overweight and obese women had Odd's redio of 1.06 and 2.27, respectively, as compared to women with normal weight.

Conclusions:

The results of the present study revealed a strong association of overweight and obesity with breast cancer in the Indian population.

Induced abortions and the risk of all cancers combined and site-specific cancers in Shanghai

Although some previous case-control studies found an increased risk of breast cancer in women who had an induced abortion, the evidence from prospective studies suggests that induced abortions do not cause breast cancer. We have assessed risks of 12 types of cancer in women who have had induced abortions in a prospective study in China. Female textile workers (n = 267,400) completed a baseline questionnaire (1989-1991) that ascertained information on the major risk factors for breast cancer, contraceptive use, and induced abortions and were actively followed until July 2000. Cox Proportional Hazards analysis was used to calculate incidence rate ratios for specific types of cancer in women who ever had an induced abortion and by number of induced abortions. Women who had had an abortion were not at increased risk of cancer. There was a significant reduction in risk of uterine corpus cancer in women who had ever had an induced abortion, and a significant decreasing trend in risk with increasing number of induced abortions. No convincing associations with other cancers were observed. Women who have induced abortions after a live birth are not at increased risk of cancer and induced abortions may reduce risk of cancer of the corpus uteri.

Oral contraceptive use as a risk factor for premenopausal breast cancer: a meta-analysis

OBJECTIVE

To perform a meta-analysis of case-control studies that addressed whether prior oral contraceptive (OC) use is associated with premenopausal breast cancer.

METHODS

We searched the MEDLINE and PubMed databases and bibliography reviews to identify case-control studies of OCs and premenopausal breast cancer published in or after 1980. Search terms used included breast neoplasms, oral contraceptives, contraceptive agents, and case-control studies. Studies reported in all languages were included. Thirty-four studies were identified that met inclusion criteria. Two reviewers extracted data from original research articles or additional data provided by study authors. We used the DerSimonian-Laird method to compute pooled odds ratios (ORs) and confidence intervals (CIs) and the Mantel-Haenszel test to assess association between OC use and cancer.

RESULTS

Use of OCs was associated with an increased risk of premenopausal breast cancer in general (OR, 1.19; 95% CI, 1.09-1.29) and across various patterns of OC use. Among studies that provided data on nulliparous and parous women separately, OC use was associated with breast cancer risk in both parous (OR, 1.29; 95% CI, 1.20-1.40) and nulliparous (OR, 1.24; 95% CI, 0.92-1.67) women. Longer duration of use did not substantially alter risk in nulliparous women (OR, 1.29; 95% CI, 0.85-1.96). Among parous women, the association was stronger when OCs were used before first full-term pregnancy (FFTP) (OR, 1.44; 95% CI, 1.28-1.62) than after FFTP (OR, 1.15; 95% CI, 1.06-1.26). The association between OC use and breast cancer risk was greatest for parous women who used OCs 4 or more years before FFTP (OR, 1.52; 95% CI, 1.26-1.82).

CONCLUSION

Use of OCs is associated with an increased risk of premenopausal breast cancer, especially with use before FFTP in parous women.

Common risk factors of breast and ovarian cancer: recent view

Clinicians, epidemiologists, and public health specialists tend to examine breast and ovarian cancer separately. Although this seems fairly rational and expected, both malignancies are estrogen related and thus share many risk factors. In this review, we investigate the common familial, reproductive, anthropometric, nutritional, and lifestyle risk factors of breast and ovarian cancer. We believe that the parallel examination of the two cancer types could significantly contribute to an improved prevention of "gynecological cancer" as a whole.

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.

Informed consent in the (mis)information age

Recent studies suggest that large numbers of health-care consumers are turning to the Internet as a source of health information. This article considers the potential impact of on-line health information on women's health-care decisions, and the role of physicians relating to their patients' use of the Internet as an information source. In particular, the article examines the effect of on-line health information on the informed consent process. Physicians' disclosure obligations (their legal duty to provide information to patients) and the law of informed consent are briefly described. The article then considers the Internet as a source of health information, and instances and types of misinformation. Finally, the article suggests steps physicians may take to help their patients benefit from Internet health information and to become critical consumers who do not fall victim to inaccurate or misleading information. The article concludes by suggesting that physicians make a practice of asking their patients about alternate sources of information they may have accessed, in order to help ensure that patients' health-care decisions are based on current, accurate, and complete information.

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.

Induced and spontaneous abortion and breast cancer risk: results from the E3N cohort study

Recent reviews reach conflicting conclusions on breast cancer risk after spontaneous or induced abortion. E3N is a large-scale cohort study collecting detailed information on environmental and reproductive factors. We investigated the relation between breast cancer and a history of induced and/or spontaneous abortion, using the data from the 100,000 women aged 40-65 at entrance in 1990. Among them, over 2,600 new invasive breast cancers had been diagnosed by June 2000. Multivariate analysis, adjusted for known potential confounders, showed no association between a history of induced abortion and breast cancer risk either in the whole population (relative risk [RR] = 0.91, 95% confidence interval [CI] 0.82-0.99) or in subgroups defined by parity or by menopausal status. Overall, the association between spontaneous abortion and breast cancer was not significant (RR = 1.05, 95% CI 0.95-1.15). However, there is a suggestion of increased risk with increased number of miscarriages (RR = 1.20, 95% CI 0.92-1.56 after 3 or more). Moreover, an interaction with menopausal status was observed. In premenopause, the risk decreased with increasing number of spontaneous abortions, whereas it increased in postmenopause. Among nulliparous and parous women, the relative risk estimates were respectively equal to 1.16 (95% CI 1.04-1.30, p trend < 0.0008) and 1.14 (95% CI 1.01-1.28, p trend = 0.005). Premenopausal breast cancer, on the other hand, appeared to be less frequent in women who had had repeated miscarriages. We conclude that there is no relationship between breast cancer and induced abortion but that an association with spontaneous abortion is possible and may depend on menopausal status.

Risk factors and risk reduction of breast and ovarian cancer

PURPOSE OF REVIEW

Breast and ovarian cancer remain a significant burden for women living in the Western world. This paper reviews the risk factors and current strategies to prevent these diseases.

RECENT FINDINGS

Established factors associated with the risk of breast cancer include family history, reproductive factors and lactation, as well as age at menarche and menopause. Hormone replacement therapy increases the risk, whereas oral contraceptives probably confer no increased risk. Alcohol moderately increases the risk, whereas a diet rich in folate and carotenoids might be protective. The role of other dietary factors, smoking and physical exercise remain unclear. Important risk factors for ovarian cancer are reproductive factors and possibly the long-term use of hormone replacement therapy. The risk is decreased by oral contraceptives. In carriers of a BRCA1 or BRCA2 gene mutation, prophylactic surgery can significantly reduce the risk of breast as well as ovarian cancer. Tamoxifen may be considered as a chemopreventive agent in women with a high risk of breast cancer, including carriers of a BRCA2 mutation, but is probably not effective in BRCA1 carriers.

SUMMARY

During the period of this review, the importance of several known risk factors was confirmed, whereas the effects of other factors became more clear. Chemoprevention and prophylactic surgery have emerged as preventative options that can reduce the risk of breast and ovarian cancer.

Breast cancer in relation to induced abortions in a cohort of Chinese women

The possible influence of induced abortion on breast cancer risk was assessed in a cohort of 267 040 women enrolled in a randomised trial of breast self-examination in Shanghai, China. Based on answers to a baseline questionnaire, subsequent breast cancer risk was not significantly associated with ever having an induced abortion. After adjustment for potential confounders, the relative risk estimate was 1.06 (95% C.I.: 0.91, 1.25), and there was no trend in risk with number of abortions. Analysis of data from more detailed interviews of 652 cases and 694 controls from the cohort yielded similar results. There was also no overall increase in risk in women with induced abortion after first birth. Few women had undergone an abortion after 13 weeks gestation or before their first child. Although increases in risk were observed in such women, they were not statistically significant and could have been due to recall bias. Abortions as they have been performed in China are not an important cause of breast cancer.

Breast cancer risk in healthy and symptomatic women: results of a multivariate analysis. A case-control study

Several risk factors for breast cancer (BC) have been investigated in different reports, but none has been really useful in preventing BC development. The aim of this study was to evaluate the risk of BC in self-selected symptomatic women in comparison with the healthy population residing in an urban area of Italy. A group of 404 women (median age 59 years, range 26-89 years) with confirmed BC (cases) were age-matched with 389 healthy women (Group A), and 391 (Group B) symptomatic non-screened patients without BC, who were referred to our Breast unit. The results of univariate analysis showed a significant (P < 0.01) difference between cases and controls in (1) age at menarche, (2) number of birth and age at first births, (3) lactation and months of lactation, and (4) estrogen replacement therapy (ERT) and duration of ERT. Multivariate analysis using a logistic regression model adjusted for age showed that five independent parameters (no pregnancy, age at first birth > 30 years, no lactation, use of ERT, ERT > 40 months) significantly (P < 0.01) correlated with BC onset. The relative odds ratios (ORs) at 95% confidence interval (95% CI) were 5.25, 2.47, 2.82, 2.80, and 5.56, respectively. The cumulative OR (95% CI) calculated from the observed vs. predicted values was 7.15. No differences (P = NS) were found between groups A and B. In conclusion, in our study population, the prolonged use (> 40 months) of ETR in menopausal women resulted in an increased risk of BC, and represented the only risk factor that could be removed.

Risk factors for breast cancer

Breast cancer is multifaceted, and multiple risk factors most likely contribute to each case of the disease. Through further elucidation of highly penetrant autosomal dominant mutations and, perhaps more importantly, weaker polygenic influences, rational therapies to treat or prevent malignancy may develop. Determining the nature and sequence of genetic changes in premalignant breast tissue may offer the greatest opportunity to alter the process of breast cancer development. Perhaps the most difficult challenge is to understand the environmental risk factors that predispose to breast cancer. Although endogenous factors such as hormonal influence on breast cancer risk have been established, this information has not greatly affected our ability to prevent or significantly reduce the risk of disease. National and regional collaborative efforts are needed to fund research directed at defining how the environment and lifestyle factors affect the risk of cancer development.