Oral contraceptives and breast disease in premenopausal Northern Albertan women

Use of Oral Contraceptives as a Potential Risk Factor for Breast Cancer: A Systematic Review and Meta-Analysis of Case-Control Studies Up to 2010

Despite numerous studies evaluating the risk of breast cancer among oral contraception users, the effect of oral contraceptive on developing breast cancer remains inconclusive. Therefore, we conducted a systematic review of literature with meta-analysis in order to quantitative estimate this association. The bibliographic database MEDLINE and EMBASE, and reference lists of identified articles were searched, with no language restrictions, from the start of publication to August 2010. We performed a reanalysis and overall estimate of 79 case-control studies conducted between 1960-2010, including a total of 72,030 incidents, histologically confirmed cases of breast cancer and 123,650 population/hospital controls. A decrease was observed in cancer risk in OC users before age 25 years (0.91, 0.83-1.00). However, the use of OCs before the first full-term pregnancy had a significant increased risk of breast cancer (OR, 1.14, 1.01-1.28, p = 0.04), as did OC use longer than 5 years (1.09, 1.01-1.18, p = 0.02). Pooled crude odds ratios of breast cancer in ever-users of oral contraceptives was 1.01 [95% confidence interval (CI), 0.95-1.07], compared with never-users. There was no significant increase in risk among premenopausal women (1.06, 0.92-1.22), postmenopausal women (0.99, 0.89-1.10), or nulliparous women (1.02, 0.82-1.26). Oral contraceptives do not appear to increase the risk of breast cancer among users. However, OC use before a first full-term pregnancy or using them longer than 5 years can modify the development of the breast cancer.

Risk Factors for Benign Breast Disease and their Relation with Breast Cancer Risk. Pooled Information from Epidemiologic Studies

Information from published case-control studies on benign breast disease was pooled using standard statistical methods to obtain single, overall risk estimates. This analysis showed that higher socio-economic status (pooled relative risk, RR = 1.24, 95% confidence interval, CI = 1.13-1.37), later menopause (pooled RR = 1.87, 95%, CI = 1.67-2.11) and late age at first birth (pooled RR = 1.30, 95%, CI = 1.13-1.50) were associated with an increased risk of benign breast disease, whereas an apparent protection was given by greater body mass index (pooled RR = 0.58, 95%, CI = 0.50-0.67) and the use of oral contraceptives (pooled RR = 0.75, 95%, CI = 0.67-0.83). The role of these factors did not appear to be materially different in the various histopathologic categories considered, although available information allowed only a general distinction between breast dysplasia (fibrocystic disease) and benign tumors, chiefly fibroadenoma. In conclusion, the general evidence from published studies indicates that benign breast lumps appear to share a number of important risk factors with breast cancer.

Risk factors for benign proliferative breast disease

BACKGROUND

As part of a nested case-control study of benign proliferative breast disease (BPBD) conducted within the cohort of women participating in the Alberta breast screening programme, an analysis of all women who had a benign breast biopsy between 1990 and 1995 was undertaken to identify the epidemiological risk factors for BPBD.

METHODS

The breast biopsies of all eligible women were re-reviewed by a panel of four pathologists using Page's classification for benign breast disease. Cases were 165 women whose biopsies, upon review, showed benign breast tissue changes ranging from sclerosing adenosis to atypical ductal hyperplasia. Controls were 217 women whose biopsies showed no evidence of any proliferative or neoplastic changes. In-person interviews were conducted with all study subjects.

RESULTS

Women with >/=25% fibroglandular breast tissue density, as compared to women with <25% density, experienced nearly a doubling in risk of BPBD (OR = 1.91, 95% CI : 1.24-2.94). All other possible risk factors examined were not associated with BPBD.

CONCLUSION

This study suggests that fibroglandular tissue density may be a risk factor, or marker, for increased risk of BPBD.

A cohort study of oral contraceptive use and risk of benign breast disease

The purpose of the cohort study reported here was to investigate the association between oral contraceptive use and risk of benign breast disease (BBD), overall and by histological subtype, within the 56,537 women in the Canadian National Breast Screening Study (NBSS) who completed self-administered lifestyle and dietary questionnaires. The NBSS is a randomized controlled trial of screening for breast cancer in women aged 40-59 at recruitment. Cases were the 2,116 women in the dietary cohort who were diagnosed with biopsy-confirmed incident BBD. For comparative purposes, a subcohort consisting of a random sample of 5,681 women (including 197 subjects with incident BBD) was selected from the full dietary cohort. After exclusions for various reasons, the analyses were based on 2,116 cases and 5,338 non-cases. There was an inverse association between use of oral contraceptives and risk of all types of BBD combined. The reduction in risk was confined largely to proliferative forms of BBD (BPED), and in particular, to those forms of BPED without histological atypia, in whom there was a progressive reduction in risk with increasing duration of use (the IRR (95% CI) for use of more than 7 years was 0.64 (0.47-0.87)); risk of BPED with atypia was increased somewhat in association with oral contraceptive use (the IRR (95% CI) for use of more than 7 years was 1.43 (0.68-3.01 )), but not in a dose-dependent manner. The results were similar when examined separately in the screened and control arms of the NBSS and for screen-detected and interval-detected BPED.

Breast-cancer risk and oral contraceptive use in Slovenian women aged 25 to 54

Results of a previous case-control study in Slovenia showed a significantly elevated risk of breast cancer for ever-OC users aged 25 to 54 years. A further study was conducted in 1988-1990 in the whole of Slovenia, employing more rigorous epidemiological methodology. Cases were 624 women with breast cancer, aged 25 to 54 years, diagnosed at the Institute of Oncology in Ljubljana and other Slovenian hospitals. Controls were 624 women identified through the Population Registry, randomly selected and matched with cases by date of birth and commune of residence. Data were collected by personal interview, using coloured photographs of packages of all OC on the Slovenian market since 1964. A calendar of reproductive life events was constructed with participants to improve estimation of exposure. The adjusted odds ratio (OR) for ever-users was 1.09. There was no increase in risk with total duration of use, interval since first use, age at starting OC, according to use before or after first delivery and time between menarche and age at first use. Increased risk (OR = 2.92) was found for OC users at the time of diagnosis and for those stopping them less than 6 months before (current users). The risk was not increased for those who stopped OC more than 6 months before diagnosis. The results of this study are consistent with most studies showing no overall effect of OC in women aged till 55 years ever using them. Increased risk of breast cancer in current OC users suggests a possible promoting effect of the pill in susceptible women, and indicates the need for careful breast surveillance of these women while they are using OC and in the period immediately following cessation.

Risk factors for histologically confirmed benign breast tumors

A case-control study of 156 cases of various types of benign breast disease (BBD) and 156 population controls was conducted to investigate the role of various behavioral, reproductive, and hormonal factors in the etiology of these breast disorders. Our results indicate that the distinct histological groups of BBD differ from each other in respect to possible risk factors. Small sample size poses severe restrictions on the conclusiveness of the results and thus they should be considered as preliminary and suggestive. Our results do not support the notion that BBD could be considered as a uniform entity with common risk factors.

Oral contraceptives and breast cancer: review of the epidemiologic literature

Oral contraceptives have caused little or no overall increase in risk of breast cancer in women in developed countries, even in long-term users or after more than two decades since initial exposure. Limited evidence suggests a possible small increase in risk in users of oral contraceptives in developing countries, and further studies of breast cancer and oral contraceptives in low risk populations are warranted. Oral contraceptives may enhance risk of breast cancer in young women with a history of benign breast disease, and this possibility should also be investigated further. Multiple investigations have fairly consistently shown risk of breast cancer in women under age 45 years to be increased slightly in long-term users of oral contraceptives. Further studies should be conducted to elucidate the mechanism of this apparent phenomenon.

[Oral contraceptives and breast cancer: analysis of the statistical power of the association]

The power of the association between oral contraceptives and breast cancer was analysed in all the papers published up to date. Seventy-seven publications (from 44 studies) were collected and graded as to quality using meta-analytical methods. Power achieved a figure of greater than or equal to 0.8 in a 10.8% of the associations studied. It showed a significant relationship with the existence of a significant relative risk of the oral contraceptives for breast cancer. The relationship with the sample size of a study was not linear. Power did not show any significant relationship to other variables related to the design of a study (apart from matching, being the power higher in unmatched studies), or to the biases detected, although studies considered as unbiased yielded a higher power. Logistic regression analysis included as predictors of a power greater than or equal to 0.80 the existence of a significant relative risk and the lack of biases in a research.

Oral contraceptives and breast cancer. Review and meta-analysis

To evaluate the relation between use of oral contraceptives and the incidence of breast cancer, the authors reviewed the epidemiologic literature and used quantitative methods to summarize the data. Study results for any use of oral contraceptives were pooled using a model that accounted for both interstudy and intrastudy variability. The authors also explored interstudy variability and modeled a duration-effect relation between oral contraceptive use and breast cancer. Case-control and follow-up studies were considered separately. Overall, the authors observed no increase in the risk of breast cancer for women who had ever used oral contraceptives, even after a long duration of use. These results were consistent across study design. However, data combined from case-control studies revealed a statistically significant positive trend (P = 0.001) in the risk of premenopausal breast cancer for women exposed to oral contraceptives for longer duration. This risk was predominant among women who used oral contraceptives for at least 4 years before their first term pregnancy (relative risk = 1.72; 95% confidence interval = 1.36 to 2.19). Additional study is required to determine whether this finding in a subgroup of exposed women is confirmed and whether the risk remains increased with advancing age.

Oral contraceptives and breast cancer

Among women in general the risk of breast cancer through 59 years of age does not appear to be affected appreciably by the use of oral contraceptives. Nonetheless, concern continues to be expressed about the effects of early age at first use, long-term duration of use, formulation, and a variety of other factors thought to influence breast cancer risk in the presence of oral contraception. A number of recent studies restricted to young women suggest that long-term use may increase the risk of disease occurring very early, but the present lack of consistent findings in well-conducted epidemiologic studies prevents any certain conclusion with regard to cause-and-effect. However, if an increased risk were indeed present, the most plausible interpretation is that long-term oral contraception promotes earlier clinical manifestation of breast cancer in some women while having no net impact on their lifetime risk of the disease.

What can a woman do about her risk of dying of breast cancer?

Every day, American women are told that one in ten will develop breast cancer, and some groups perceive their risk to be so high as to justify immediate bilateral mastectomy. Many associations with breast cancer have been identified, including a history of benign breast diseases, in situ carcinoma, a family history of breast cancer, prolonged menstruation as a result of early menarche or delayed menopause, few or late pregnancies, excessive alcohol intake, obesity, and possibly the use of estrogens as oral contraceptives or postmenopausal replacement therapy. In spite of these associations, our understanding of either the cause(s) of breast cancer or the sequence of events leading to a diagnosis of breast cancer is still inadequate to make global public health recommendations regarding life style--or even to initiate well-designed studies. The epidemiologic evidence strongly suggests, however, that events relatively early in a woman's life are more important than later events, even though most of the risk of developing breast cancer will be expressed after the age of 75. Possibly one of the greatest contributions we can make to our patients' welfare is to share the knowledge that the risk of dying of breast cancer is considerably smaller than the risk of developing breast cancer; that the risk of early death from breast cancer rarely exceeds 10% in even the highest risk groups; and that the life styles most likely to reduce the risk of cardiovascular disease and other scourges of womankind are also those most likely to reduce the risk of developing breast cancer.

Breast cancer and combined oral contraceptives: results from a multinational study. The WHO Collaborative Study of Neoplasia and Steroid Contraceptives

A collaborative, hospital-based case-control study was conducted at 12 participating centres in 10 countries. Based on data from personal interviews of 2,116 women with newly diagnosed breast cancer and 12,077 controls, the relative risk of breast cancer in women who ever used oral contraceptives was estimated to be 1.15 (1.02, 1.29). Estimated values of this relative risk based on data from three developed and seven developing countries were 1.07 (0.91, 1.26) and 1.24 (1.05, 1.47) respectively; these estimates are not significantly different (P = 0.22). Estimates for women under and over age 35 were 1.26 (0.95, 1.66) and 1.12 (0.98, 1.27), respectively, and these estimates are also not significantly different (P = 0.38). Risk was highest in recent and current users and declined with time since last use regardless of use. Risk did not increase with duration of use after stratifying on time since last use. Risk did not increase significantly with increasing duration of use before age 25 or before a first live birth. However, a relative risk of 1.5 that was of borderline statistical significance was observed in women who used oral contraceptives for more than 2 years before age 25. No single source of bias or confounding was identified that could explain the small increases in risk that were observed. Chance alone is also an unlikely explanation. The results could be due to a combination of chance and potential sources of bias, or they could represent a weak causal relationship.

The role of exogenous hormones in the epidemiology of breast, ovarian and endometrial cancer

This review focuses on the effects of oral contraceptives (OC) and estrogen replacement therapy (ERT) on the risk of breast, ovarian and endometrial cancer. The relationship between OC and cancer risk is first placed in a historical perspective. Since 1960, when OC were introduced, the hormonal composition of OC as well as the characteristics of the OC user have changed considerably. Studies conducted in the 1970s were generally reassuring, but it was not until the 1980s that studies could evaluate the effect of prolonged OC use after an extended follow-up period. Although the relationship between breast cancer and OC has been investigated in about 40 studies, the issue still remains essentially unresolved. Most studies report no association between ever use of OC and breast cancer risk. Several studies find increased risk for prolonged use and other studies report elevated risks for women who used OC very early in their reproductive years. The inconsistent results of recent studies are attributed to bias or to geographical variation in latency period elapsed, types of OC preparations, or prevalence of other risk factors. In contrast, the use of combined OC has consistently been shown to reduce the risk of ovarian and endometrial cancer. The risk further decreases with increasing duration of use and the protective effect seems to persist in ex-users for at least 5 years. Some evidence indicates that higher parity reduces the protective effect. Though studies relating ERT to breast cancer are far from consistent, overall, there is evidence for a moderately increased risk with high dose and/or long duration. The effect seems to be modified by mode of administration (injections vs. pills) and by type of ERT, but this needs confirmation. The number of adequate studies on the relationship between ERT and ovarian cancer is too small to draw firm conclusions. The positive relationship between ERT and endometrial cancer is now well established. The ERT effect is dose- and duration-dependent and is characterized by a short latency period. The cyclic addition of progesterone (greater than 10 days/cycle) may reduce the risk increase.

Oral contraceptives and breast cancer: results from an expanded case-control study

The relationship between oral contraceptives and breast cancer was evaluated among 2,022 cases and 2,183 controls participating in a multicentre breast cancer screening programme. Ever use of oral contraceptives was not related to breast cancer risk (RR = 1.0, 95% CI 0.9-1.2), and no overall patterns of increasing or decreasing risks were observed according to the duration of use, or time since first or most recent use. Although we had no women with extended periods of oral contraceptive use early in life, no evidence of adverse effects attributable to short-term use before age 25, before first live birth or during the perimenopausal period were observed. Further, oral contraceptives did not interact with other breast cancer risk factors, except among those with a history of two or more breast biopsies (RR = 2.0). Analyses by stage of disease revealed that risk was related to the duration of oral contraceptive use: greater than or equal to 5 years use was associated with reduced risk for in situ cancer (RR = 0.59) and increased risks for invasive cancers (RR = 1.5 and 1.4 respectively for small and large lesions). These data suggest that oral contraceptive effects may vary by stage of disease, but provide no overall evidence of an association between oral contraceptives and breast cancer.

Cancer of the breast and reproductive tract in relation to use of oral contraceptives

Effects of oral contraception on cancers of the female breast and reproductive tract are critically reviewed from human studies reported since 1980. The cumulative risk of breast cancer through 59 years of age appears to bear no relationship to oral contraceptive (OC) use whatsoever. Studies restricted to women under age 45, however, raise concern about a possible adverse effect from OC use before a first-term pregnancy. A duration-related protective effect against endometrial cancer occurs from use of combined OCs. The risk is reduced by about 40% with 2 years of use, and by about 60% with 4 or more years of oral contraception. Oral contraception in excess of 3 years protects against ovarian cancer. Four years of use confers a 50% reduction in risk and 7 or more years of use confers a 60%-80% reduction in ovarian cancer risk. Studies of cervical dysplasia and carcinoma in situ suggest elevated risks with 2 or more years of OC use, although results are difficult to interpret in view of numerous factors that might distort the findings. The risk of invasive cervical cancer appear to be unaffected by up to 5 years of oral contraception. Beyond this, there is evidence suggesting an elevated risk which approaches a 2-fold increase at 10 years of use. Cancers of the vagina and fallopian tube are extremely rare. Their risks have yet to be characterized in relation to oral contraception.

Oral contraceptives and breast cancer. A review

Case-control and cohort studies published between 1977 and 1988 were reviewed with the purpose to evaluate the relationship between use of oral contraceptives (OC-use) and breast cancer risk, tumour biology and tumour prognosis with special emphasis on early OC-use. The risk of breast cancer was assessed in 30 case-referent studies and 5 cohort studies, and the prognosis of breast cancer had been studied in 9 reports. Definition of OC-use, prevalence of OC-use, latency time between start of OC-use and tumour diagnosis, case identification and choice of referents, study size, study quality were assessed. The outcome of the studies is presented. From the results of the analyses the author concludes that there is no overall risk for breast cancer among OC-users. However, with the emphasis on early OC-use, consistent results seem to emerge showing an increased risk of premenopausal breast cancer, when the possible bias of different latency times is taken into account. Also results on breast cancer incidence in early exposed age groups, tumour biology and prognosis in early OC-users with breast cancer support a genuine risk relationship. The effects of different OC-brands and dose, and the risk of peri- and postmenopausal breast cancer after early OC-use can at present not be assessed.

Risk factors as an indicator for breast cancer screening in asymptomatic patients

A review of breast carcinoma risk factors has established that age and sex are dominant variables. Additional epidemiological factors include family history, past medical history, menstrual status, age at birth of first child, demographic factors and reproductive history, which are of established importance as major or minor risk determinants for breast cancer. Taking into account the various epidemiological correlations and the multifactorial aetiology of this type of carcinoma, there is only a small probability that the identification of known risk factors will enable conclusive identification or prevention of the disease. Nevertheless the recognition of known risk factors may enhance screening efforts through surveillance, more selective biopsies and interval xeromammography. Total ductoglandular mastectomy may possibly be considered a beneficial approach to the management of the high-risk patient in whom preinvasive disease is detected. The identification of the high-risk patient is of paramount importance for prophylaxis. Prospective clinical trials using diagnostic approaches may include the study of genetic markers, hormones and steroid metabolites, mammographic parenchymal patterns and the analysis of genetic pedigree or other undetermined risk markers. While screening and detection programmes for breast carcinoma are not cost-effective, these intensive surveillance procedures do allow the early identification of high-risk individuals with the disease. The formulation of screening programmes which incorporate major and minor risk determinants may enhance the effectiveness of efforts to achieve diagnosis at a prognostically favourable stage of disease. Established diagnoses of stage 0 or stage I disease will translate as direct benefits to survival and reductions in economic morbidity.

Oral contraceptives and breast cancer. In vitro effect of contraceptive steroids on human mammary cell growth

The proliferative response of human mammary epithelial cells cultured in medium containing oral contraceptive steroids, singly and in combination, was measured. Cells came from 59 normal, nonmalignant atypical, and malignant breast tissue specimens. Growth of most cultures was stimulated by the estrogens 17 beta-estradiol and ethinyl estradiol, and any combination containing ethinyl estradiol. Most (75%) malignant specimens were stimulated by one or more of the progestins, whereas none of the nonmalignant cells were. For two of the estrogen/progestin combinations found in many birth control pills, malignant cells were stimulated to grow faster than nonmalignant cells. It was concluded that oral contraceptive steroids can stimulate the growth of mammary epithelia in cell culture and might do the same in vivo. These data corroborate epidemiologic data which suggest oral contraceptives might act as tumor promoters, especially in the older user, who is more likely to have malignant cells already present in the breast.

Breast cancer and oral contraceptives: a review

The relationship between oral contraceptive use and breast cancer was investigated in 22 major epidemiological studies, which are reviewed in this paper. The overall risk ratio was never found to increase when computed among all users vs. nonusers. Risk increases were found in some studies within specific subgroups; but in general, if any risk exists, it is not much more than one. Future studies should focus specifically on women under age 25, on women before a first full-term pregnancy and, to a lesser extent, on perimenopausal women and on women who have had a benign breast disease.

Oral contraceptives and prognosis of breast cancer in women aged 35 to 50

Among 193 breast cancer patients aged 35-50 years, there was no appreciable difference in the extent of disease at diagnosis between 53 oral contraceptive (OC) users and 140 OC non-users. There was no overall significant difference between OC users and non-users for either the disease-free interval (P = .81), metastatic period (P = .41), or survival (P = .79), either alone or when adjusted for stage or family history. The survival rate of OC users of more than 2 years was similar to the survival rate of those of shorter duration (P = .36). Patients who began the use of OC 10 years or more before diagnosis showed no statistical difference from those beginning more recently (P = .69). Recent OC users within a year of diagnosis had a survival rate similar to that of other users who stopped the pills at least 1 year prior to diagnosis (P = .14). Our data suggest no adverse effects of OC use on the prognosis of breast cancer, regardless of duration of use, latency or recency period.

Interactions between benign breast disease and other risk factors for breast cancer

A population-based incident case-control study of breast cancer in Northern Alberta, Canada, provided an opportunity to evaluate interactions between the occurrence of benign breast disease (BBD) and other potential risk factors. Overall there was a 2-fold excess risk of breast cancer among women with BBD. This excess persisted regardless of the number of years from first biopsy for BBD to diagnosis of breast cancer, suggesting a permanent alternation in risk with BBD. Significant variations of the BBD--breast cancer association were noted with several factors. The excess risk of breast cancer among women with BBD was enhanced by having a later age at menarche, a later age at first birth, or lower parity. The usual protective effect of late age at menarche was seen only among women without BBD, and was supplanted by a 4-fold elevated risk among women with BBD. The deleterious effects of later age at first birth and nulliparity were greater among women with BBD. These patterns generally support the notion that hormonal factors mediate the relation between BBD and the development of breast cancer.

Access to data and the information explosion: oral contraceptives and risk of cancer

This report describes a technically feasible method to deal with the enormous volume of literature published regarding oral contraceptives. This subject was discussed in 3735 publications during the period from November 1977 through October 1980. Our findings showed that those papers reporting original, numeric relationships involving risk of cancer and use of oral contraceptives were one percent of the total 3735 publications. However, only seven of the 27 articles involved were authored by individuals from departments of obstetrics and gynecology. Further, only four of the 27 were published in journals devoted to obstetrics and gynecology. The analyses suggest a form of censorship taking place, in that the obstetrics/gynecology specialists do not have ready access to the primary data.

Oral contraceptive use and early abortion as risk factors for breast cancer in young women

A case-control study was conducted in Los Angeles County, California, of 163 very young breast-cancer cases (all aged 32 or less at diagnosis) to investigate the role, if any, of oral contraceptives (OC) in the development of the disease. OC use before first full-term pregnancy (FFTP) was associated with an elevated risk, which increased with duration of OC use (relative risk approximately 2.2 at 6 years of use, P < 0.01). This increased risk could not be explained by other risk factors. OC use after FFTP was not associated with any change in risk. A first-trimester abortion before FFTP, whether spontaneous or induced, was associated with a 2.4-fold increase in breast-cancer risk (P < 0.005).

Family history and oral contraceptives: unique relationships in breast cancer patients

The relative frequency of a history of breast cancer among specific blood relatives was determined for breast cancer patients according to their prior use of oral contraceptives (OC). These data were compared with those derived from patients having various types of noninvasive breast lesions and from control women. It was found that a history of breast cancer among grandmothers or aunts was significantly more frequent among breast cancer patients who had used OC for one or more years continuously than among OC-negative breast cancer patients, and among patients with noninvasive breast lesions and control women, regardless of OC usage. Breast cancer patients whose grandmothers or aunts had breast cancer used OC significantly more frequently than did family history (FH)-negative breast cancer patients and breast cancer patients having a history of breast cancer limited to relatives other than grandmothers and aunts (mothers, sisters, cousins). It appears that the family history is a significant covariable in the relationship between OC usage and breast cancer. There is a need for specific studies to test the possibilities that OC usage increases the risk of breast cancer among women whose grandmothers or aunts had breast cancer, and reduces the risk of breast cancer in FH-negative women.