Differential effects of reproductive factors on the risk of pre- and postmenopausal breast cancer. Results from a large cohort of French women

The aim of this study was to obtain a better understanding of the role of hormonal factors in breast cancer risk and to determine whether the effect of reproductive events differs according to age at diagnosis. It analysed the effect of age at menarche, age at first full-term pregnancy, number of full-term pregnancies and number of spontaneous abortions both on the overall risk of breast cancer and on its pre- or postmenopausal onset, using the data on 1718 breast cancer cases, obtained from a large sample of around 100000 French women participating in the E3N cohort study. The results provide further evidence that the overall risk of breast cancer increases with decreasing age at menarche, increasing age at first pregnancy and low parity. No overall effect of spontaneous abortions was observed. The effect of these reproductive factors differed according to menopausal status. Age at menarche had an effect on premenopausal breast cancer risk, with a decrease in risk with increasing age of 7% per year (P<0.05). Compared to those who had their first menstrual periods at 11 or before, women experiencing menarche at 15 or after had an RR of 0.66 (95% CI 0.45-0.97) in the premenopausal group. Age at first full-term pregnancy had an effect on both pre- and postmenopausal breast cancer risk, with significant tests showing increasing risk per year of increasing age (P=0.001 and P<0.05 respectively). A first full-term pregnancy above age 30 conveyed a risk of 1.63 (95% CI 1.12-2.38) and 1.35 (95% CI 1.02-1.78) in the pre- and postmenopausal groups respectively. A protective effect of high parity was observed only for postmenopausal breast cancer risk (P for trend test =0.001), with point estimates of 0.79 (95% CI 0.60-1.04), 0.69 (95% CI 0.54-0.88), 0.66 (95% CI 0.51-0.85) and 0.64 (95% CI 0.48-0.86) associated to a one, two, three and four or more full-term pregnancies. A history of spontaneous abortion had no significant effect on the risk of breast cancer diagnosed before or after menopause. Our results suggest that reproductive events have complex effects on the risk of breast cancer.     

A cohort study of reproductive factors and family history of breast cancer in southern Sweden

Background. Studies have been contradictory regarding the hypothesis that reproductive risk factors of breast cancer as parity and age at first full-term pregnancy (AFFP) operate differently in women with and without a family history of breast cancer. Methods. The overall tumour incidence and breast cancer incidence related to fertility factors were followed in a population based cohort of 29,508 women aged 25–65 when interviewed between 1990 and 1992 in south Sweden. At the end of the follow up in December 1999, the cohort constituted 226,611 person years. The risk of breast cancer in relation to reproductive factors were studied in women with at least one first degree relative with breast cancer and compared with women without a family history. Findings. A total of 1145 malignant tumours were seen and 1166.6 were expected (SIR = 0.98, 95% CI = 0.93–1.04). Slightly more breast cancer cases were seen 434 than expected 387.69 (SIR = 1.12, 95% CI = 1.02–1.23). A family history of breast cancer among a first degree relative was present in 1615 women. Forty-five breast cancers were seen among these women while 24.27 was expectecd (SIR = 1.85, 95% CI = 1.35–2.48). Nulliparous women with a family history of breast cancer had a higher risk of breast cancer, SIR = 1.76, 95% CI = 0.64–3.82, compared with nulliparous women without a family history, SIR = 1.13, 95% CI 0.99–1.29. Similarly women with parity 1–2 with a family history had a higher SIR = 1.81, 95% CI = 1.16–2.69 compared with women without a family history having 1–2 children, SIR = 1.13, 95% CI = 0.99–1.29. In women with 3 children those with a family history continued to have a high SIR = 1.98, 95% CI = 1.11–3.27 compared with women without a family history SIR = 0.90, 95% CI = 0.73–1.09. An early full-term pregnancy was protective in both groups. A higher risk than nulliparous women were seen after age 25 in the family history group and after age 30 in the sporadic cancer group. Interpretation. Women with a first degree family history of breast cancer do not experience the same protection from a high number of pregnancies as women without a family history. However, an early first full-term pregnancy seems to offer a substantial protection in the family history group if undertaken before age 20. This suggest that reproductive factors tend to operate differently in the two groups of 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. © 1995 Wiley-Liss, Inc.     

Spontaneous and induced abortions and risk of breast cancer.

The relationship between spontaneous or induced abortion and the risk of breast cancer was analyzed in a case-control study conducted in the greater Milan area on 2,394 cases of breast cancer and 2,218 controls in hospital for a spectrum of acute conditions, not gynecological, hormonal or neoplastic. No consistent relationship emerged between spontaneous or induced abortion and breast cancer: compared with women reporting no abortions (spontaneous or induced), the multivariate relative risk (RR) was 1.0 (95% confidence interval, CI, 0.9 to 1.2) in those reporting one abortion and 0.9 (95% CI 0.7 to 1.0) in those reporting two or more. This lack of association was consistent in strata of age and parity, including younger women. We further analyzed the risk of breast cancer associated with an abortion before and after full-term pregnancy. Compared with parous women reporting no induced or spontaneous abortions, those who had an abortion before their first full-term pregnancy had about a 20% higher risk of breast cancer. This finding, however, was not statistically significant (RR 1.2, 95% CI 0.9 to 1.7). No increased risk was observed in women who had had a first abortion after a full-term pregnancy (RR 0.9, 95% CI 0.8 to 1.0). This study does not support the hypothesis that spontaneous or induced abortion appreciably influences subsequent breast-cancer risk.     

Association of time since last birth,age at first birth and parity with breast cancer survival among parous women: A register‐based study from Norway

Reproductive factors that have a well‐documented effect on breast cancer risk may also influence the prognosis of the disease, but previous studies on breast cancer survival have yielded conflicting results. We combined information from two population‐based registries and obtained information on 16,970 parous women with invasive breast cancer. Cox regression analysis was used to assess breast cancer survival in relation to age at diagnosis, age at first birth, time since last birth and parity. We stratified the analyses by age at diagnosis (<50 and ≥50 years) as an approximation for menopausal age. In women diagnosed before 50 years of age, breast cancer survival was reduced with younger age at diagnosis (p for trend <0.001), whereas in women diagnosed at 50 years or later, survival was reduced with older age at diagnosis (p for trend 0.011). For breast cancer diagnosed before 50 years, survival was poorer in women with four or more births compared to women with one or two births (hazard ratio 1.3, 95% confidence interval 1.1–1.6). A short time since last birth was associated with reduced survival (p for trend 0.05), but adjustment for stage and grade attenuated the association. Among women diagnosed at 50 years or later, we found no association with survival for any of the reproductive factors. In summary, reproductive factors were associated with survival from breast cancer diagnosed before but not after age 50 years. Young women had a particularly poor prognosis throughout the study period.     

Parity,age at first birth and the risk of carcinoma in situ of the breast

Epidemiological studies of in situ breast cancer are sparse, and the role of reproductive history, an established risk modifier for invasive breast cancer, remains incompletely investigated. To examine possible associations with parity and age at first birth, we undertook a case-control study nested in a nationwide cohort of Swedish women. The reproductive history of 1,368 women aged 65 or younger with a diagnosis of carcinoma in situ of the breast were compared with that of 6,837 age-matched controls drawn randomly from a population-based Fertility Registry. Statistical analyses were performed by conditional logistic regression. Compared to nulliparous women, ever-parous women were at a reduced risk of carcinoma in situ of the breast. The risk decreased with number of live births, with the estimated risk reduction in the highest parity group (5+), being of the same magnitude as that reported for invasive breast cancer. By contrast, a positive association with increasing age at first birth was somewhat less pronounced than that observed previously in the same data set with respect to invasive breast cancer. Our findings indicate that parity affects the risk of invasive breast cancer and carcinoma in situ similarly, whereas the effect of age at first birth appears to be weaker for the risk of carcinoma in situ. Int. J. Cancer 77:330–332, 1998. © 1998 Wiley-Liss, Inc.     

Reproductive factors and risk of breast cancer by tumor subtypes among Ghanaian women: A population-based case–control study

Higher proportions of early-onset and estrogen receptor (ER) negative cancers are observed in women of African ancestry than in women of European ancestry. Differences in risk factor distributions and associations by age at diagnosis and ER status may explain this disparity. We analyzed data from 1,126 cases (aged 18–74 years) with invasive breast cancer and 2,106 controls recruited from a population-based case–control study in Ghana. Odds ratios (OR) and 95% confidence intervals (CI) were estimated for menstrual and reproductive factors using polytomous logistic regression models adjusted for potential confounders. Among controls, medians for age at menarche, parity, age at first birth, and breastfeeding/pregnancy were 15 years, 4 births, 20 years and 18 months, respectively. For women ≥50 years, parity and extended breastfeeding were associated with decreased risks: >5 births vs. nulliparous, OR 0.40 (95% CI 0.20–0.83) and 0.71 (95% CI 0.51–0.98) for ≥19 vs. <13 breastfeeding months/pregnancy, which did not differ by ER. In contrast, for earlier onset cases (<50 years) parity was associated with increased risk for ER-negative tumors (p-heterogeneity by ER = 0.02), which was offset by extended breastfeeding. Similar associations were observed by intrinsic-like subtypes. Less consistent relationships were observed with ages at menarche and first birth. Reproductive risk factor distributions are different from European populations but exhibited etiologic heterogeneity by age at diagnosis and ER status similar to other populations. Differences in reproductive patterns and subtype heterogeneity are consistent with racial disparities in subtype distributions.     

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. Int. J. Cancer 73:503–507, 1997. © 1997 Wiley-Liss, Inc.     

Reproductive factors associated with breast cancer risk in northern Iran

Breast cancer is a common malignancy for women in most parts of the world and the incidence in Iranian women is growing. The patients are relatively younger than their western counterparts. The aim of study was to investigate the roles of reproductive factors for breast cancer in Babol. In a case–control study in Babol, we recruited a total of 100 new patients with histologically confirmed breast cancer and 200 age-matched controls selected from outpatient clinics. Demographic and reproductive factors were ascertained by in-person interview using a constructed questionnaire. Several potential confounding factors were adjusted using multiple logistic model. The adjusted odds ratio showed that having higher age at first pregnancy and abortion were associated with increased breast cancer risk (the adjusted OR = 4.1, 95% CI: 1.3–13.2 and 2.93, 95% CI: 1.64–5.24, respectively). By increasing parity, the risk had reduced significantly; among women with parity ≥5, the adjusted OR was 0.09 (95% CI 0.01–0.7) compared with nulliparous women, and also for each additional parity, the risk reduced by 50% (OR = 0.50, 95% CI: 0.34–0.71). The duration of breast feeding was inversely associated with breast cancer risk, while after additional adjustment for parity, no longer the protective effect of breast feeding was observed. Nulliparity, late age at first birth and abortion were the most important reproductive factors associated with breast cancer risk; therefore, it is recommended to women with these risk factors to perform breast cancer screening tests earlier.     

Age at any birth and breast cancer risk

In an effort to assess the relative importance of age at first birth, age at subsequent births, and total parity to the occurrence of breast cancer, reproductive data from 4,225 women with breast cancer and 12,307 hospitalized women without breast cancer were analyzed by a multiple logistic regression model. Age at first birth was confirmed to be the most important reproductive risk indicator; it was associated with a 3.5 % increase of relative risk for every year of increase in age at first birth (the 95 % confidence interval of this estimate was 2.3 to 4.7 % increase per year). However, age at any birth after the first was also an independent and statistically significant risk indicator; it was associated with a 0.9% increase of relative risk for every year of increase in age at any (and every) birth (the 95 % confidence interval of this estimate was 0.4 to 1.5 % increase per year). There is evidence that the age of approximately 35 years represents for every birth a critical point; before this age any full-term pregnancy confers some degree of protection; after this age any full-term pregnancy appears to be associated with increase in breast cancer risk. The effect of parity is determined by the age of occurrence of the component pregnancies. While most pregnancies occur under the age of 35, the distribution varies from population to population, and this may account for the differences between populations in whether or not a protective effect is seen for births after the first, and if it is seen, its extent.     

A case-control study of breast cancer in Tianjin, China.

In a population-based case-control study of breast cancer in Tianjin, China, involving 300 cases and 300 population controls interviewed during 1985-1986, a number of strong risk factors were identified. Although average age at menarche was late by Western standards in this developing country (14.4 years), it was clearly related to risk. Women with their first menstrual period at age 12 years or earlier had 80% greater risk than women who started at age 17 years or later. Age at first full-term pregnancy was also strongly related to risk, with women whose first birth after age 30 years having 3.2 times the risk of women whose first birth was under age 20 years. Other established breast cancer risk factors in Western populations (family history of breast cancer, a history of benign breast disease, and use of oral contraceptives late in reproductive life) were also risk factors in this population. Parity and duration of lactation were both strongly protective against breast cancer development in univariate analyses. These two variables were highly correlated with each other and with age at first full-term pregnancy. Although the effects of each variable dissipated somewhat in multivariate analysis, our data strongly suggest that both parity and lactation independently contribute to breast cancer risk.     

Risk of breast cancer in relation to reproductive factors in Denmark

The effect of reproductive factors on breast cancer risk was evaluated in a population-based case-control study, including 1,486 breast cancer cases diagnosed over a one-year period in Denmark. They were identified from the files of the nationwide trial of the Danish Breast Cancer Co-operative group and the Danish Cancer Registry. The control group was an age-stratified random sample of 1,336 women from the general population. Data on risk factors were collected by self-administered (mailed) questionnaires. Significantly increased relative risks (RR) were associated with never being pregnant (RR = 1.47), an early terminated first pregnancy (RR = 1.43), and having a natural menopause after the age of 54 (RR = 1.67). Trends of decreasing risk were observed by increasing parity and age at menarche. These findings were independent of age at first full-term pregnancy which overall was not related to breast cancer risk, though a weak association appeared in women less than 50 years at diagnosis. The study confirmed that pregnancies must continue to term to offer protection against breast cancer.     

Reproductive factors,exogenous female hormone use and breast cancer risk in Japanese: the Miyagi Cohort Study

The incidence of breast cancer among Japanese women is substantially increasing. This population-based prospective cohort study in Japan evaluated the associations of reproductive factors and exogenous female hormone use with breast cancer risk, both overall and separately among premenopausal and postmenopausal women. A total of 24,064 women aged 40–64 were followed from 1990 to 2003. During 309,424 person-years of follow-up, 285 breast cancer cases were documented. In overall evaluation, nulliparity was significantly associated with an increased risk of breast cancer. There was a significant decrease in risk with increasing parity number among parous women (trend P = 0.008). No association was observed between age at menarche or age at first birth and breast cancer risk. Neither oral contraceptive (OC) use nor the use of exogenous female hormones other than OC was associated with breast cancer risk. The evaluation according to menopausal status revealed that nulliparity and parity number were significantly related to breast cancer risk only among postmenopausal women. Later age at natural menopause was associated with an increased risk of breast cancer among postmenopausal women (trend P = 0.02). Our findings suggest that parity number and age at menopause have great effects on breast cancer risk among Japanese women.     

Early oral contraceptive use and breast cancer among premenopausal women: final report from a study in southern Sweden

In southern Sweden during the 1960s, women began to use oral contraceptives (OCs) extensively at a young age. This case-control study investigates the relationship between the use of OCs and breast cancer development in women in southern Sweden diagnosed in the early 1980s. The risk for breast cancer after OC use among premenopausal women was modeled, after adjustment was made for age, age at menarche, and age at first full-term pregnancy or parity. Both the duration of OC use before 25 years of age and commencement of OC use at a young age were associated with a significant increase in the risk of breast cancer as well as a significant trend. The duration of OC use before the first full-term pregnancy was associated with an increased risk of breast cancer, but it did not show a significant trend. The total duration of OC use was weakly, but not significantly, associated with breast cancer development. The odds ratio for women starting OC use before 20 years of age was 5.8 [95% confidence interval (CI), 2.6-12.8]; for women using OCs for greater than 5 years before age 25, it was 5.3 (95% CI, 2.1-13.2); and for women using OCs for greater than or equal to 8 years before first full-term pregnancy, it was 2.0 (95% CI, 0.8-4.7). In multivariate analyses including the different measurements of OC use, only starting age of OC use was significantly associated with breast cancer. The exposure-response relationship between duration of OC use and risk of breast cancer depended on the age at first use of OCs. Given a fixed duration of OC use, the risk increased with younger starting age of OC use. The findings point to the importance of the early reproductive years as risk determinants for breast cancer after OC use.     

Epidemiology of basal-like breast cancer

Risk factors for the newly identified “intrinsic” breast cancer subtypes (luminal A, luminal B, basal-like and human epidermal growth factor receptor 2-positive/estrogen receptor-negative) were determined in the Carolina Breast Cancer Study, a population-based, case–control study of African-American and white women. Immunohistochemical markers were used to subtype 1,424 cases of invasive and in situ breast cancer, and case subtypes were compared to 2,022 controls. Luminal A, the most common subtype, exhibited risk factors typically reported for breast cancer in previous studies, including inverse associations for increased parity and younger age at first full-term pregnancy. Basal-like cases exhibited several associations that were opposite to those observed for luminal A, including increased risk for parity and younger age at first term full-term pregnancy. Longer duration breastfeeding, increasing number of children breastfed, and increasing number of months breastfeeding per child were each associated with reduced risk of basal-like breast cancer, but not luminal A. Women with multiple live births who did not breastfeed and women who used medications to suppress lactation were at increased risk of basal-like, but not luminal A, breast cancer. Elevated waist-hip ratio was associated with increased risk of luminal A in postmenopausal women, and increased risk of basal-like breast cancer in pre- and postmenopausal women. The prevalence of basal-like breast cancer was highest among premenopausal African-American women, who also showed the highest prevalence of basal-like risk factors. Among younger African-American women, we estimate that up to 68% of basal-like breast cancer could be prevented by promoting breastfeeding and reducing abdominal adiposity. An erratum to this article can be found at     

Reproductive factors and hormone receptor status among very young (<35 years) breast cancer patients

The prognosis for breast cancer occurs in young women is usually poor. The impact of different reproductive factors on disease characteristics is still largely unknown. We analyzed 261 patients aged ≤35 years old who were treated at the Cancer Hospital of Fudan University, Shanghai, China. The relationships between certain reproductive factors (age at menarche, parity, number of children, breastfeeding, history of abortion, age at first full-term pregnancy and oral contraceptive (OC) use) and disease characteristics were evaluated. Compared with patients who experienced fewer full-term pregnancies (<2 times), the patients with more full-term pregnancies (≥2 times) exhibited higher percentage of ER-positive tumors (61.5%) (P = 0.015), and patients whose age of menarche was ≥15 years exhibited a greater chance of PR-positive tumors (64.8%) (P = 0.036) compared with those whose age of menarche was <15 years old. Additionally, patients who had taken OCs were more likely to present with late-stage tumors (II stage or later) (87.5%) (P = 0.002) than patients who had never taken OCs. Our study provides evidence that women with more full-term pregnancies and later age at menarche are more possible to exhibit hormone receptor-positive tumors. Additionally, patients who have taken OCs are more likely to present with advanced disease.     

Maternal age,parity, and pregnancy estrogens

Total estrogens (TE), estradiol (E2), estriol (E3), and human placental lactogen (hPL) were determined by radioimmunoassay in the blood of 126 pregnant women during their 26th and 31st weeks of pregnancy and the results were studied in relation to maternal age and parity. Total estrogens and E2 were lowest among the youngest women (<20 years) and highest among women aged 20–24 years, whereas older women (25 + years) had, on the average, intermediate values. For E3 the pattern was qualitatively similar to that of TE and E2 but less striking, and no maternal age pattern was evident with respect to hPL. Within maternal age groups, TE and E2 were higher among women in the first, than among those in their second, full-term pregnancy; the difference was about seven percent for TE (P=0.14) and about 14 percent for E2 (P=0.05). No parity patterns were evident with respect to E3 and hPL. There were fairly strong correlations between the determinations of the same hormone in the same woman during the 26th and 31st weeks of pregnancy; Pearson correlation coefficients were 0.60 for TE, 0.78 for E2, 0.60 for E3, and 0.72 for hPL. Since the risk of breast cancer increases apparently monotonically with maternal age at birth, the present data are equivocal with respect to the hypothesis linking levels of pregnancy estrogens to risk of breast cancer in the offspring. However, the data are compatible with hypotheses linking excessive pregnancy-estrogen exposure to conditions more common among first-born individuals, including testicular cancer and cryptorchidism.Drs Panagiotopoulou, Katsouyanni, Petridou, Garas, and Tzonou are from the Department of Hygiene and Epidemiology, University of AThens Medical School, Greece, and Dr Trichopoulos, to whom correspondence should be addressed, is from the Department of Epidemiology, Harvard School of Public Health, 677 Huntington Avenue, Boston, MA 02115, USA. This study was supported by a grant from the Greek Ministry of Youth.     

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.     

A record-based evaluation of induced abortion and breast cancer risk (United States)

Objective:Previous studies of induced abortion and breast cancer may have been limited by differential reporting of abortion history. We conducted a population-based case–control study to evaluate abortion (both induced and spontaneous) and breast cancer risk. Methods:All study subjects were aged 20–69 years and members of Group Health Cooperative of Puget Sound (GHC). Incident invasive breast cancer cases (n = 138) were identified from the linkage between the GHC enrollment file and the Seattle–Puget Sound SEER Cancer Registry. Controls (n = 252) were randomly selected from GHC enrollment files and matched to cases on age and enrollment period. All subjects had to have been enrolled at GHC for the 2 years preceding diagnosis (cases) or reference (controls) date. The unified medical record of each case was abstracted for pregnancy history, including prior induced and spontaneous abortions, menopause status, height and weight, screening practices, and other risk factors. Results:Compared to all women who had never had an induced abortion, the multivariate adjusted relative risk of breast cancer in women with an induced abortion was 0.9 (95% confidence interval 0.5–1.6). This risk was similar in parous women, and nulliparous women. There was no association between spontaneous abortion and breast cancer risk. Conclusions:These results do not support a relation between induced abortion and breast cancer incidence.     

Reproductive history and breast cancer in a population of high fertility, Costa Rica, 1984-85

The relationship between breast cancer and women's reproductive history in Costa Rica was analyzed using logistic regression methods on data from 171 breast cancer cases and 826 population-based controls aged 25-58 years. The risk of breast cancer in nulliparous women under age 45 was 3 times that for parous women in the same age group. Women over 44 years of age with a parity greater than 4 had a risk of breast cancer of 0.3 compared to women of the same age but with a parity of 1-4. Neither breast-feeding nor birth interval showed an overall association with breast cancer independent of parity. Women with early age at first birth had a lower relative risk of breast cancer than women aged 20-24 at first birth, but only in two subgroups--women aged 45 and over and women with parity 1-4. Women without a completed pregnancy in the last 20 years had an elevated relative risk. However, results are not conclusive because some information is probably distorted by recall errors. Declines in fertility rates in the 1960s and 1970s may result in an increase of 30% in breast cancer incidence in Costa Rica between 1980 and the year 2000, according to the relative risks found in this study. In contrast, the effect of childlessness will probably not produce significant changes in national breast cancer trends.