Difficulty becoming pregnant and family history as interactive risk factors for postmenopausal breast cancer: the Iowa Women's Health Study

A prospective cohort study of infertility and cancer incidence

OBJECTIVE

To investigate the association between infertility and the incidence of invasive cancer.

DESIGN

Prospective cohort study (1989-2015).

SETTING

Not applicable.

PATIENT(S)

A total of 103,080 women aged 25-42 years in the Nurses' Health Study II who were cancer-free at baseline (1989).

INTERVENTION(S)

The infertility status (failure to conceive after 1 year of regular, unprotected sex) and causes of infertility were self-reported at baseline and biennial follow-up questionnaires.

MAIN OUTCOME MEASURE(S)

Cancer diagnosis was confirmed through medical record review and classified as obesity-related (colorectal, gallbladder, kidney, multiple myeloma, thyroid, pancreatic, esophageal, gastric, liver, endometrial, ovarian, and postmenopausal breast) or non-obesity-related (all other cancers). We fit the Cox proportional-hazards models to estimate the hazard ratios (HRs) and 95% confidence intervals (CIs) of the association between infertility and cancer incidence.

RESULT(S)

During 2,149,385 person-years of follow-up, 26,208 women reported a history of infertility, and we documented 6,925 incident invasive cancer cases. After adjusting for body mass index and other risk factors, women who reported infertility had a higher risk of developing cancer than gravid women without a history of infertility (HR, 1.07; 95% CI, 1.02-1.13). This association was stronger among obesity-related cancers (HR, 1.13; 95% CI, 1.05-1.22; vs. non-obesity-related cancers, HR, 0.98; 95% CI, 0.91-1.06) and, in particular, obesity-related reproductive cancers (postmenopausal breast, endometrial, and ovarian cancers; HR, 1.17; 95% CI, 1.06-1.29) and was stronger among women who first reported infertility earlier in life (≤25 years, HR, 1.19; 95% CI, 1.07-1.33; 26-30 years, HR, 1.11; 95% CI, 0.99-1.25; >30 years, HR, 1.07; 95% CI, 0.94-1.22; P trend < .001).

CONCLUSION(S)

A history of infertility may be associated with the risk of developing obesity-related reproductive cancers; further study is needed to elucidate the underlying mechanisms.

The association between the multiple birth and breast cancer incidence: an update of a systematic review and meta-analysis from 1983 to 2022

BACKGROUND

It has been assumed that perinatal factors such as multiple pregnancies may affect subsequent breast cancer risk in the mother. Considering the inconsistencies in the results of case-control and cohort studies published in the world, this meta-analysis was conducted in order to determine the exact association between multiple pregnancies (twins or more) and the breast cancer incidence.

METHODS

This study was performed as a meta-analysis based on PRISMA guidelines by searching the international databases of PubMed (Medline), Scopus, and Web of Science as well as by screening selected articles based on their subject, abstract and full text. The search time was from January 1983 to November 2022. Then the NOS checklist was used to evaluate the quality of the final selected articles. The indicators considered for the meta-analysis included the odds ratio (OR) and the risk ratio (RR) along with the confidence interval reported in the selected primary studies. The desired analyzes were performed with STATA software version 17 to be reported.

RESULTS

In this meta-analysis, 19 studies were finally selected for analysis, which fully met the inclusion criteria. Of these, 11 were case-control studies and 8 were cohort ones. Their sample size was 263,956 women (48,696 with breast cancer and 215,260 healthy) and 1,658,378 (63,328 twin or multiple pregnancies and 1,595,050 singleton pregnancies), respectively. After combining the results of cohort and case-control studies, the effect of multiple pregnancies on the breast cancer incidence was equal to 1.01 (95% CI: 0.89-1.14; I2: 44.88%, P: 0.06) and 0.89 (95% CI: 0.83-0.95; I2: 41.73%, P: 0.07), respectively.

CONCLUSION

The present meta-analysis results showed, in general, multiple pregnancies were one of the preventive factors of breast cancer.

Mammographic breast density in infertile and parous women

Background

Mammographic breast density is a useful marker for breast cancer risk, as breast density is considered one of the strongest breast cancer risk factors. The study objective was to evaluate and compare mammographic breast density in infertile and parous women, as infertility may be associated with high breast density and cancer occurrence.

Methods

This study evaluated mammographic breast density using two different systems, BIRADS and Boyd. A selected patient population of 151 women with primary infertility (case group) was compared to 154 parous women who had at least one previous pregnancy (control group). Both groups were premenopausal women aged ≥35.

Results

Evaluation of mammographic features showed that 66.9 % of case group patients and 53.9 % of control group patients were classified BIRADS-3/BIRADS-4; p < 0.05. Adjusted Odds ratio for the case group in the categories BIRADS-3/BIRADS-4 was 1.78 (95 % CI: 1.10-2.89). Using the Boyd classification system, 53.6 % of case group patients and 31.8 % of control group patients were classified E/F; p < 0.05. Adjusted Odds ratio for case group patients in Boyd categories E/F was 2.05 (95 % CI: 1.07-3.93).

Conclusions

Both systems yielded a higher percentage of increased breast density in the case group. Boyd and BIRADS classification systems indicate to what extend breast cancer lesions may be missed on mammography due to masking by dense tissue. Therefore, patients with a high BIRADS or Boyd score should undergo further investigation.

The possible association between IVF and breast cancer incidence

BACKGROUND

The possible association between ovulation-inducing drugs and breast cancer development has been debated. Our aim was to evaluate the incidence of breast cancer in a cohort of women exposed to in vitro fertilization (IVF).

METHODS

A retrospective cohort analysis was performed by linkage of the computerized database of all women treated at the IVF Unit at Assaf Harofeh Medical Center between 1986 and 2003, and the Israeli National Cancer Registry. The standardized incidence ratio (SIR) was computed as the ratio between the observed number of breast cancer cases and the expected cases, adjusted for age and continent of birth, in the general population. Tumor characteristics of the IVF patients were studied by reviewing original medical records.

RESULTS

35 breast carcinomas were diagnosed among 3,375 IVF-treated women, compared to 24.8 cases expected (SIR = 1.4; 95% CI 0.98-1.96). Age >or=40 years at IVF treatment (SIR = 1.9; 95% CI 0.97-3.30), hormonal infertility (SIR = 3.1; 95% CI 0.99-7.22), and >or=4 IVF cycles (SIR = 2.0; 95% CI 1.15-3.27) were found to be risk factors to develop breast cancer compared to the general population. Multivariate analysis revealed that women who underwent >or=4 IVF cycles compared to those with one to three cycles were at risk to develop breast cancer, although not significantly (SIR = 1.9; 95% CI 0.95-3.81). Of IVF-treated women 85% had ER(+) tumors and 29% had positive family history.

CONCLUSIONS

A possible association between IVF therapy and breast cancer development was demonstrated, especially in women >or=40 years of age. These preliminary findings need to be replicated in other cohort studies.

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.

Interactions between genetic and reproductive factors in breast cancer risk in a population-based sample of African-American families

Incidence of breast cancer (BC) varies among ethnic groups, with higher rates in white than in African-American women. Until now, most epidemiological and genetic studies have been carried out in white women. To investigate whether interactions between genetic and reproductive risk factors may explain part of the ethnic disparity in BC incidence, a genetic epidemiology study was conducted, between 1989 and 1994, at the Howard University Cancer Center (Washington, DC), which led to the recruitment of 245 African-American families. Segregation analysis of BC was performed by use of the class D regressive logistic model that allows for censored data to account for a variable age of onset of disease, as implemented in the REGRESS program. Segregation analysis of BC was consistent with a putative dominant gene effect (P < 0.000001) and residual sister-dependence (P < 0.0001). This putative gene was found to interact significantly with age at menarche (P = 0.048), and an interaction with a history of spontaneous abortions was suggested (P = 0.08). A late age at menarche increased BC risk in gene carriers but had a protective effect in non-gene carriers. A history of spontaneous abortions had a protective effect in gene carriers and increased BC risk in non-gene carriers. Our findings agree partially with a similar analysis of French families showing a significant gene x parity interaction and a suggestive gene x age at menarche interaction. Investigating gene x risk factor interactions in different populations may have important implications for further biological investigations and for BC risk assessment.

[Epidemiological characteristics of breast cancer development in pre and postmenopausal women]

BACKGROUND

To study the relation between breast cancer and different risk factors, personal, familial and demographic factors. An statistic and epidemiologic study was also carried on a whole population of women and then classified on pre and postmenopausal women.

PATIENTS AND METHODS

A matched case-control study was performed based on age, urban area and hormonal activity. Total population was composed by 274 cases and same number of controls. Studied variables were obtained by a questionnaire asking for study level, reproductive and personal history, familial considerations and lifestyles. A multiples logistic regression model was made.

RESULTS

Over total population, late menarcheal age, late first pregnancy, and familial history of breast cancer were shown as independent risk factors, but a low study level, and oral contraception were shown as protective factors. This risk model was confirmed on postmenopausal women but no over premenopausal women, so in this group, main risk factors were familial breast cancer history and a medical history of benign breast disease. Moreover, the low study level was also a protective factor.

CONCLUSIONS

Familial history of breast cancer in mothers or sisters was the main risk factor for breast cancer, mainly in premenopausal women, and low study level showed as protective factor.

Variation in the interaction between familial and reproductive factors on the risk of breast cancer according to age, menopausal status, and degree of familiality

BACKGROUND

Studies have found that reproductive factors might have a variable effect on the occurrence of breast cancer (BC) according to the existence or not of a family history of BC. The effect of a family history of BC on the risk of BC may also vary according to the age at diagnosis and the degree of kinship. This may confound the relation between familial risk and reproductive factors. A combined analysis was performed to study the interaction between familial risk and reproductive factors according to degree of familiality, age at interview and menopausal status.

METHODS

The present analysis included 2948 cases and 4170 controls in seven case-control studies from four countries. The combined relative risks were estimated using a Bayesian random-effects logistic regression model.

RESULTS

The main effects of reproductive life factors on the risk of BC are in agreement with previous studies. Two-way interactions between subject's age or menopausal status and a family history of BC were not significant. Although the three-way interaction between age, familial risk and parity was not significant, familial risk seemed to be increased slightly for women with high parity compared with women with low parity in the older age group, and seemed to be slightly decreased for women with high parity compared with women with low parity in younger women. The subject's age also appeared to have an effect on the interaction between familial risk and the age at first childbirth (P = 0.1).

CONCLUSIONS

A possible influence of reproductive and menstrual factors on familial risk of BC has been suggested previously and was also evident in the present study. Three-way interactions between age, family history and parity or age at first childbirth might exist and they merit further investigation.

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.

Cancer risk following radiotherapy for infertility or menstrual disorders

A cohort of 968 Israeli women treated with radiotherapy for infertility was followed up for cancer incidence. The majority of the subjects were irradiated to both the ovaries and the pituitary gland. Mean doses to the brain, colon, ovary and bone marrow were 0. 8, 0.6, 1.0 and 0.4 Gy, respectively. More than 10 years after radiation treatment, 60 cancers were observed compared with 74.5 expected based on national cancer incidence rates (standardized incidence ratio 0.81, 95% confidence interval 0.61-1.04). No statistically significant excess or deficit was seen for any individual type of cancer; however, a non-significant 60% increased risk of colon cancer was observed. Risk of colon cancer was higher among women with 2 or more treatments and increased with length of follow-up. A decreased risk of breast cancer was suggested. Neither age at exposure nor attained age modified subsequent cancer risk. No clear excess of any cancer site was observed among women at organ doses above the median compared with subjects at doses below the median, except a slight increase in colon cancer. No significant excess incidence of cancer was demonstrated in this small cohort of patients treated with radiotherapy for infertility. Our results are consistent with those from an earlier study of cancer mortality among women receiving radiotherapy for infertility conducted in New York City. Int. J. Cancer 82:795-798, 1999. Published 1999 Wiley-Liss, Inc.

The effects of interaction between familial and reproductive factors on breast cancer risk: a combined analysis of seven case-control studies

In this paper, a combined analysis was performed to study the interaction between familial risk and reproductive life factors. In particular, the interaction between familial risk and breast cell mitotic activity (BCMA), as assessed by duration of ovarian activity, was investigated because of the potential importance of mitotic activity on genetically susceptible cells. The present analysis included 3152 cases and 4404 controls in seven case-control studies from four countries. The interaction effect was estimated in each study separately, then combined using two different methods: a multivariate weighted average and a Bayesian random-effects model. The main effects of reproductive life factors on the risk of breast cancer were in agreement with the previous findings. In particular, an increased duration of BCMA before the first childbirth and over life was found to increase the risk of breast cancer (P < 0.001). Slightly increasing but non-significant, familial risks were observed with increasing number of children (P = 0.17), increasing age at first childbirth (P > 0.2) and increasing duration of BCMA (P > 0.2). There was no modification in familial risk with age at menarche and no clear pattern with menopause characteristics. A weak influence of reproductive and menstrual factors on the familial risk emerged from the present study.

Family history and risk of breast cancer in New Zealand

A national population-based case-control study was used to assess the influence on breast cancer risk of a family history of the disease and the possibility of an interaction with reproductive risk factors. A total of 891 women aged 25-54 years with a first diagnosis of breast cancer and 1,864 control subjects randomly selected from the electoral rolls were interviewed. Age-adjusted relative risks (RR) of breast cancer were similar for mothers (RR = 2.3) and sisters (RR = 2.7) but somewhat higher for first-degree (RR = 2.6) than for second-degree (RR = 1.7) relatives. Cases reporting a first- or second-degree relative with breast cancer were no more likely to be diagnosed at an early age than those with no family history. With regard to the age at diagnosis of the relative, the RR was higher if breast cancer had been diagnosed before the age of 45 years than later; this was true for first-degree as well as for second-degree relatives. In women with no family history, the falling RRs with increasing age at menarche reflected the usual pattern, but no such trend was apparent in those reporting a mother or sister with breast cancer. For age at first full-term pregnancy, parity, breast-feeding, menopausal status, infertility, history of benign breast disease and body mass index, no evidence was seen of effect modification by a family history of breast cancer. Mothers of cases had about twice the cumulative rate of breast cancer as mothers of controls, a similar difference being seen between sisters of cases and sisters of controls.

Induction of ovulation and risk of breast cancer: an overview and perspectives

The modern techniques for assisted reproduction have exposed many women to potent follicular stimulation regimens. Follicular stimulation is associated with an exposure to potent fertility drugs and abnormal estrogen, progesterone and human chorionic gonadotropin (hCG) concentrations. These treatments and hormones might affect the proliferation of epithelial breast cells and thus the risk of breast cancer. The possible effects of ovarian stimulation on the incidence and course of human breast cancer, and the need for long-term cohort studies is discussed.

Interactions between genetic and reproductive factors in breast cancer risk in a French family sample

Considerable progress has been made in the characterization of the genetic component of breast cancer (BC). However, BC still remains a complex disease involving a genetic component and many other risk factors essentially linked to reproductive-life factors. To search for interactions between genetic and reproductive-life factors in the etiology of BC, a systematic family study was performed in two French hospitals from December 1987 to January 1990 and led to recruitment of 288 families, the IGRC data ("IGRC" refers to the Institut Gustave Roussy and Institut Curie, where the data were obtained). Detailed information on reproductive factors was recorded for probands and female first-degree relatives. Segregation analysis of BC was conducted by taking into account a variable age at onset of disease, by use of the class D regressive logistic model, as implemented in the REGRESS computer program. Segregation analyses of BC in IGRC data showed evidence for the segregation of a dominant gene and additional sister-sister dependence, both when reproductive factors were ignored and when they were included. A significant interaction was detected between the dominant gene and age when reproductive factors were taken into account. Among the reproductive factors included in segregation analysis, parity was found to interact with the dominant-gene effect, and there was an indication of an interaction, albeit not significant, between the dominant gene and age at menarche. Whereas the usual protective effect conferred on breast-cancer risk by high parity remained in nonsusceptible women, it disappeared in susceptible women. The increased BC risk associated with a late age at menarche was higher in susceptible women than in nonsusceptible women. Interactions between inherited predisposition to BC and reproductive factors were detected here for the first time by segregation analysis. It would be of major interest to confirm these results by family studies in other populations.

Induced abortion and the risk of breast cancer

BACKGROUND

It has been hypothesized that an interrupted pregnancy might increase a woman's risk of breast cancer because breast cells could proliferate without the later protective effect of differentiation.

METHODS

We established a population-based cohort with information on parity and vital status consisting of all Danish women born from April 1, 1935, through March 31, 1978. Through linkage with the National Registry of Induced Abortions, information on the number and dates of induced abortions among those women was combined with information on the gestational age of each aborted fetus. All new cases of breast cancer were identified through linkage with the Danish Cancer Registry.

RESULTS

In the cohort of 1.5 million women (28.5 million person-years), we identified 370,715 induced abortions among 280,965 women (2.7 million person-years) and 10,246 women with breast cancer. After adjustment for known risk factors, induced abortion was not associated with an increased risk of breast cancer (relative risk, 1.00; 95 percent confidence interval, 0.94 to 1.06). No increases in risk were found in subgroups defined according to age at abortion, parity, time since abortion, or age at diagnosis of breast cancer. The relative risk of breast cancer increased with increasing gestational age of the fetus at the time of the most recent induced abortion: <7 weeks, 0.81 (95 percent confidence interval, 0.58 to 1.13); 7 to 8 weeks, 1.01 (0.89 to 1.14); 9 to 10 weeks, 1.00 >12 weeks, 1.38 (1.00 to 1.90) (reference category, 9 to 10 weeks).

CONCLUSIONS

Induced abortions have no overall effect on the risk of breast cancer.

Modifying effect of reproductive risk factors on the age at onset of breast cancer for German BRCA1 mutation carriers

Female carriers of mutations in the BRCA1 gene on chromosome 17q have a very high risk of developing breast and/or ovarian cancer during their lifetime. There is, however, little knowledge of to what extent non-genetic risk factors, such as age at menarche, age at first birth, and body mass index, alter the age at onset of disease. We identified individuals showing a high probability of linkage to BRCA1 and examined the effect of other known risk factors on disease risk. A total of 43 families with at least three breast or ovarian cancer cases, including two affected before 60 years of age, were studied for linkage to the susceptibility locus BRCA1. Blood samples from relevant family members were used to genotype for at least three chromosome 17q polymorphic markers. Information on reproductive history, hormone use and lifestyle factors was collected from female members using a self-administered questionnaire. Diagnoses of breast and ovarian cancer were verified through pathology reports and paraffin blocks were obtained when available. Multipoint LOD (logarithm of the odds) scores were calculated and individuals from 10 families with a posteriori probability for linkage greater than 0.90 were used for further analysis. Forty-six BRCA1 carriers were identified by the disease haplotype; 30 were affected with breast cancer and 5 with ovarian cancer. Proportional- hazards analysis of age at onset of breast cancer yielded increased relative risks of 1.74 for early age at menarche (< 14 years), 1.58 for late age at first birth (> or = 25 years) or nulliparity, and 2.78 for recent year of birth (> or = 1940); however, none of the risk estimates was statistically significant. When both breast and ovarian cancer were considered as disease endpoints, the birth cohort effect was stronger and age at first birth showed no effect. Our data provide some evidence that reproductive risk factors for breast cancer have an effect on age at onset for BRCA1 carriers. However, considering that our analyses were based on limited numbers, these results warrant further clarification.

Induced abortion as an independent risk factor for breast cancer: a comprehensive review and meta-analysis

STUDY OBJECTIVE

To ascertain, from the published reports to date, whether or not a significantly increased risk of breast cancer is specifically attributable to a history of induced abortion, independent of spontaneous abortion and age at first full term pregnancy (or first live birth); to establish the relative magnitude of such risk increase as may be found, and to ascertain and quantify such risk increases as may pertain to particular subpopulations of women exposed to induced abortion; in particular, nulliparous women and parous women exposed before compared with after the first full term pregnancy.

INCLUDED STUDIES

The meta-analysis includes all 28 published reports which include specific data on induced abortion and breast cancer incidence. Since some study data are presented in more than one report, the 28 reports were determined to constitute 23 independent studies. Overall induced abortion odds ratios and odds ratios for the different subpopulations were calculated using an average weighted according to the inverse of the variance. An overall unweighted average was also computed for comparison. No quality criteria were imposed, but a narrative review of all included studies is presented for the reader's use in assessing the quality of individual studies. EXCLUDED STUDIES: All 33 published reports including data on abortion and breast cancer incidence but either pertaining only to spontaneous abortion or to abortion without specification as to whether it was induced or spontaneous. These studies are listed for the reader's information.

RESULTS

The overall odds ratio (for any induced abortion exposure; n = 21 studies) was 1.3 (95% confidence interval of 1.2, 1.4). For comparison, the unweighted overall odds ratio was 1.4 (1.3,1.6). The odds ratio for nulliparous women was 1.3 (1.0,1.6), that for abortion before the first term pregnancy in parous women was 1.5 (1.2,1.8), and that for abortion after the first term pregnancy was 1.3 (1.1,1.5).

CONCLUSIONS

The results support the inclusion of induced abortion among significant independent risk factors for breast cancer, regardless of parity or timing of abortion relative to the first term pregnancy. Although the increase in risk was relatively low, the high incidence of both breast cancer and induced abortion suggest a substantial impact of thousands of excess cases per year currently, and a potentially much greater impact in the next century, as the first cohort of women exposed to legal induced abortion continues to age.

Abortion and breast cancer risk

The relationship between spontaneous and induced abortions and breast cancer risk was analyzed using data from a case-control study conducted between June 1991 and February 1994 in 6 Italian centers on 2,569 histologically confirmed incident breast cancer cases and 2,588 controls admitted to hospital for a wide range of acute, non-neoplastic, non-hormone-related diseases. One or more abortions were reported by 31% of cases and 32% of controls, corresponding to a multivariate odds ratio (OR) of 1.0 (95% confidence interval [CI], 0.8-1.1). No trend in risk was observed with increasing number of total abortions or spontaneous and induced abortions separately. No significant relationship was found between the risk of breast cancer and history of spontaneous or induced or total abortions in separate strata of age at diagnosis, number of children, time of abortion in relation to first birth and family history of breast cancer. When abortion was the outcome of the first pregnancy, the OR was 1.2 for spontaneous and 1.3 for induced abortion, in relation to women with birth as outcome of the first pregnancy, and 1.0 and 1.1, respectively, when the reference category was nulligravidae. Thus, our results indicate a lack of association between induced and spontaneous abortions and breast cancer risk.

Spontaneous abortion and risk of fatal breast cancer in a prospective cohort of United States women

Controversy exists over the possible relationship between induced and spontaneous abortion and risk of breast cancer. Thus, the association of fatal breast cancer and spontaneous abortion was examined in a large prospective study of United States adult women. After seven years of follow-up, 1,247 cases of fatal breast cancer were observed among 579,274 women who were cancer-free at interview in 1982 and who provided complete reproductive histories. Results from Cox proportional hazards models, adjusted for other risk factors, showed no association between a history of spontaneous abortion and risk of fatal breast cancer (rate ratio [RR] = 0.89, 95 percent confidence interval [CI] = 0.78-1.02). The RR did not increase with increasing numbers of abortions. Parous women who had a spontaneous abortion before their first term birth were not at increased risk compared with parous women with no history of spontaneous abortion (RR = 0.76, CI = 0.54-1.05). Women whose only pregnancy ended in a spontaneous abortion were not at increased risk compared with women who were never pregnant (RR = 0.61, CI = 0.27-1.38) or whose only pregnancy ended in a livebirth (RR = 0.72, CI = 0.32-1.65). These findings do not support an association between spontaneous abortion and fatal breast cancer.

Familial risk, abortion and their interactive effect on the risk of breast cancer--a combined analysis of six case-control studies

In a previous study in France, we reported that the relative risk of breast cancer associated with a family history of breast cancer was higher in those subjects with a history of abortions. The present study was undertaken to check the existence of this interaction in other studies and to investigate whether the interaction is modified by the time at which abortions occur. Data were obtained from six case-control studies in France, Australia and Russia, with information on family history of breast cancer and abortion for 2693 breast cancer cases and 3493 controls. The interaction effect was estimated in each study separately, then combined using a multivariate weighted average. The relative risk conferred by a family history of breast cancer increased with the number of abortions (1.8 for no abortion, 1.9 for one abortion, 2.8 for two or more). There was a significant interaction between total number of abortions and family history (P = 0.04), but this was no longer significant when adjusted for other risk factors. The familial risk was highest for those who had had an abortion before first childbirth (1.9 for abortion after first childbirth, 2.7 for abortion before first childbirth). The adjusted risk associated with family history was significantly higher in those with an abortion before first childbirth (P = 0.04). Our findings suggest a synergism between familial factors and abortion. The interaction was not substantially modified by the type of abortion (spontaneous or induced) but was modified by the time at which it occurred in relation to first childbirth. This suggests an effect of abortion itself rather than predisposition to abortion. Further studies of breast cancer cases, particularly among BRCA1 gene carriers and their families, could improve our understanding of this effect.

Interaction of family history of breast cancer and dietary antioxidants with breast cancer risk (New York, United States)

We sought to determine if specific dietary antioxidants may be particularly effective in reducing breast cancer risk for women reporting family history (FH) of breast cancer in a first-degree relative. Interviews regarding usual diet, health, and family histories were conducted with 262 premenopausal and 371 postmenopausal women with incident, primary breast cancer from western New York (United States). These women were frequency-matched by age and county of residence with community controls. Among premenopausal women, there was a significant interaction between FH and alpha-tocopherol; alpha-tocopherol was associated with significantly decreased risk among FH+ women (adjusted fourth-quartile odds ratio [OR] = 0.01, 95 percent confidence interval [CI] = 0.0-0.3). This association was much weaker for FH- women [OR = 0.7, CI = 0.4-1.2]. For FH- women, a significant inverse association was observed between beta-carotene and premenopausal breast-cancer risk (OR = 0.4, CI = 0.3-0.5), but not for FH+ women (OR = 0.5, CI = 0.1-4.0). Similar relationships, although not as strong, were noted among postmenopausal women. Although limited by small numbers, these results suggest that biologic mechanisms of tumorigenesis may differ in FH+ and FH- women, and that alpha-tocopherol may be a potential chemopreventive agent for women with a family history of breast cancer, particularly premenopausal women.

Abortion and the risk of breast cancer: a case-control study in Greece

We have examined the association between induced or spontaneous abortion and breast cancer risk in Greece. In a hospital-based case-control study in Athens, 820 patients with confirmed breast cancer were compared with 795 orthopedic patient controls and 753 healthy visitor controls, matched to cases by age and interviewer. Logistic regression was used to analyze the data, controlling for demographic, reproductive and nutritional variables. Odds ratio (OR) patterns were similar for the 2 control series, which were therefore combined to increase precision of the estimates. The risk for breast cancer was not increased for women who had a history of abortion, compared to nulliparous women with no history of abortion. Thus ORs and 95% confidence intervals were for nulliparous women with spontaneous abortion, 1.17 (0.64-2.13); for nulliparous women with induced abortion, 0.98 (0.56-1.73); for parous women with no abortion, 0.56 (0.31-1.01); for parous women with spontaneous abortion, 0.61 (0.33-1.14) and for parous women with induced abortion, 0.99 (0.56-1.74). When the analysis was restricted to parous women, using parous women with no history of abortion as the baseline, ORs and 95% confidence intervals were for induced abortion before first full-term pregnancy, 2.06 (1.45-2.90); for induced abortion after first full-term pregnancy, 1.59 (1.24-2.04) and for spontaneous abortion, 1.10 (0.82-1.40). Our findings suggest that an interrupted pregnancy does not impart the long-term protective effect of a full-term pregnancy attributable to terminal differentiation.

Abortion and breast cancer risk in seven countries

Epidemiologic studies have been inconsistent in suggesting an association between abortion and breast cancer risk. Whether the protection provided by a full-term pregnancy also results from a short-term pregnancy or whether a prematurely terminated pregnancy could increase the risk of breast cancer is unclear. Data from a large, international collaborative study were used to evaluate the association between abortions, whether spontaneous or induced, and breast cancer risk. The data from seven countries included 3,958 breast cancer cases and 11,538 hospital controls with information on abortion history obtained through interviews. Compared with nulliparous women with no abortion (baseline), the odds ratios (OR) and 95 percent confidence intervals (CI) were: for nulliparous women with a history of prior abortion, 0.86 (CI = 0.68-1.08); for parous women with no history of abortion, 0.63 (CI = 0.57-0.69); for parous women with abortion before first birth, 0.82 (CI = 0.69-0.97); and, for parous women with abortion only after first birth, 0.70 (CI = 0.63-0.79). When restricting analysis to parous women, those with a history of abortion exhibited an elevated OR suggesting a 29 percent risk increase if the incomplete pregnancy occurred before first birth (CI = 1.16-1.36) and an 11 percent risk increase for abortion only after first birth (CI = 1.02-1.20) compared with women without such history. The associations observed were stronger among the youngest women. These results do not support a large overall association between abortion and breast cancer risk.

Cohorts and privacy

The extent to which major cohort studies now rely on centralized machine-readable files of personal records is taken largely for granted by investigators, but not by the public, privacy advocates, politicians, or the popular press. When widespread linkage into personal histories for statistical studies was first envisaged a few decades ago, it was regarded as impractical. But privacy advocates now fear the statistical uses even more than the administrative applications, perhaps because the latter are inevitable to prevent abuses, and often are associated with monetary benefits or personal convenience. Indeed a concept of 'privacy' has arisen that is deemed to be violated even in statistical studies where confidentiality is assured, unless the particular purpose is approved by all individuals. This concept motivates much of the political thinking. What could be lost to preventive medicine and clinical testing by this is illustrated with data from cohort studies reported in this journal (CCC) in 1993.