Age-specific differences in the relationship between oral contraceptive use and breast cancer

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

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

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

OBJECTIVE

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

METHODS

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

RESULTS

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

CONCLUSION

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

Previous oral contraceptive use and breast cancer risk according to hormone replacement therapy use among postmenopausal women

OBJECTIVE

To assess postmenopausal breast cancer risk in relation to particular patterns of oral contraceptive (OC) use according to hormone replacement therapy (HRT) exposure.

METHODS

Time-dependent Cox regression models were used to analyse information on postmenopausal women from a large-scale French cohort. Among a total of 68,670 women born between 1925 and 1950, 1405 primary invasive postmenopausal breast cancer cases were identified from 1992 to 2000.

RESULTS

A non-significant decrease in risk of around 10% was associated with ever OC use as compared to never OC use in postmenopausal women. No significant interaction was found between OC and HRT use on postmenopausal breast cancer risk. Breast cancer risk decreased significantly with increasing time since first OC use (test for trend: p=0.01); this was consistent after adjustment for duration of use or for time since last use.

CONCLUSION

No increase in breast cancer risk was associated with previous OC exposure among postmenopausal women, probably because the induction window had closed. Some women may develop breast cancer soon after exposure to OCs, leading to a deficit of cases of older women. Further investigation is therefore required to identify young women at high risk.

Impact of teenage oral contraceptive use in a population-based series of early-onset breast cancer cases who have undergone BRCA mutation testing

Oral contraceptive (OC) use in young women has been associated with an increased risk of breast cancer. This matched case-control study aims to elucidate the combined effects of OC use and genetic factors in a population-based series of BRCA1/2 mutation-tested early-onset breast cancers. A first invasive breast cancer was diagnosed in 259 women aged 40 years between 1990 and 1995 in the South Swedish Health Care Region. A total of 245 women were included in this study. Information on family history of cancer, reproductive factors, smoking and OC use was obtained from questionnaires or patient charts. Three age-matched controls per case were chosen from a prospective South Swedish cohort. Ever OC use and current OC use were not associated with breast cancer. Cases were more likely to have used OCs before age 20 years (adjusted odds ratio (OR) 2.10 (95% CI 1.32-3.33)) and before their first child (adjusted OR 1.63 (95% CI 1.02-2.62)). When stratified by age, the effect of early OC use was limited to women diagnosed prior to age 36 years (OR 1.53 (1.17-1.99) per year of OC use prior to age 20 years). The risks were similar for low-dose and high-dose OCs. The probability of being a BRCA1/2 mutation carrier was three times higher among cases who started OC use prior to age 20 years compared with cases who started at age 20 years or older or who had never used OCs. However, the duration of OC use was similar among cases with and without BRCA1/2 mutations. No association was seen with a first-degree family history of breast cancer. Each year of OC use prior to age 20 years conferred a significantly increased risk for early-onset breast cancer, while there was no risk associated with use after age 20 years.

Hormonal content and potency of oral contraceptives and breast cancer risk among young women

Recent use of oral contraceptive pills is associated with a modest risk of breast cancer among very young women. In this US population-based case-control study, we evaluated whether the excess risk associated with recent oral contraceptive use is ubiquitous for all pill types or attributable to specific oral contraceptive preparations. Hormonal content and potency of combination oral contraceptives used for the longest duration within 5 years of interview for breast cancer cases aged 20-44 years (N=1640) were compared with age-matched community controls (N=1492). Women who recently used oral contraceptives containing more than 35 microg of ethinyl oestradiol per pill were at higher risk of breast cancer than users of lower dose preparations when compared to never users (respective relative risks of 1.99 and 1.27, P(trend)<0.01). This relationship was more marked among women <35 years of age, where risks associated with high- and low-dose ethinyl oestradiol use were 3.62 and 1.91 (P(trend)<0.01), respectively. We also found significant trends of increasing breast cancer risk for pills with higher progestin and oestrogen potencies (P(trend)<0.05), which were most pronounced among women aged <35 years of age (P(trend)<0.01). Risk was similar across recently used progestin types. Our findings suggest that newer low-potency/low oestrogen dose oral contraceptives may impart a lower risk of breast cancer than that associated with earlier high-potency/high-dose preparations.

Statistical inference for familial disease clusters

In many epidemiologic studies, the first indication of an environmental or genetic contribution to the disease is the way in which the diseased cases cluster within the same family units. The concept of clustering is contrasted with incidence. We assume that all individuals are exchangeable except for their disease status. This assumption is used to provide an exact test of the initial hypothesis of no familial link with the disease, conditional on the number of diseased cases and the distribution of the sizes of the various family units. New parametric generalizations of binomial sampling models are described to provide measures of the effect size of the disease clustering. We consider models and an example that takes covariates into account. Ascertainment bias is described and the appropriate sampling distribution is demonstrated. Four numerical examples with real data illustrate these methods.

Long-term oral contraceptive use increases breast cancer risk in women over 55 years of age: the DOM cohort

The role of past oral contraceptive use in the development of breast cancer is unclear, particularly in postmenopausal women. The authors investigated this relationship among pre- and postmenopausal middle-aged women in a nested case-control study within the population-based DOM cohort, Utrecht, the Netherlands. Among a total population of 12,184 women followed up for an average of 7.5 years, 309 breast cancer cases aged 42 to 63 years, diagnosed from November 1982 through May 1996, and 610 controls were examined. Overall, duration of oral contraceptive use was not clearly related to breast cancer. In women older than 55 years, however, oral contraceptive use for more than 10 years was associated with a 2-fold increased risk of breast cancer (odds ratio (OR) 2.1, 95% confidence interval (CI) 1.1-4.0). We conclude that long duration of oral contraceptive use increases the risk of breast cancer in women over 55 years of age but not in younger women.

Tubal sterilization: focus on the U.S. experience

OBJECTIVE

To review the frequency, effectiveness, and clinical sequelae of tubal sterilization with a focus on the U.S. experience.

DESIGN

A review of U.S. health care statistics and English-language literature using a MEDLINE search, bibliographies of key references, and U.S. government publications.

PATIENT(S)

Women seeking tubal sterilization.

INTERVENTION

Tubal sterilization.

MAIN OUTCOME MEASURE(S)

Effectiveness and long-term risks and benefits.

RESULT(S)

Half of the 700,000 annual bilateral tubal sterilizations (TS) are performed postpartum and half as ambulatory interval procedures. Eleven million U.S. women 15-44 years of age rely on TS for contraception. Failure rates vary by method with one third or more resulting in ectopic pregnancy. Reversal is most successful after use of methods that destroy the least tube. Evidence of menstrual or hormonal disturbance after TS is weak, although some studies find higher rates of hysterectomy among previously sterilized women. Decreased risk of subsequent ovarian cancer has been observed among sterilized women.

CONCLUSION(S)

Tubal sterilization is highly effective and safe. Failures, although uncommon, occur at higher rates than previously appreciated. Evidence for hormonal or menstrual changes due to TS is weak. Tubal sterilization is associated with decreased risk of ovarian cancer.

Oral contraceptives and breast cancer risk in Taiwan, a country of low incidence of breast cancer and low use of oral contraceptives

One hundred and seventy four (81% of all) pathologically confirmed new incident cases of female breast cancer identified from a medical center in Taipei from February, 1993 to June, 1994 were selected as the case group. Four hundred and fifty three inpatient controls who were without obstetric-gynecological, breast, or malignant diseases were individually matched for each case by age and date of admission. Information was obtained through direct interview and review of medical records. Conditional logistic regression was used to estimate the effects of each risk factor. After adjusting for education level, body mass index, age at menarche and first full-term pregnancy, parity, menopausal status and age at menopause, lifetime lactation, use of lactation inhibition hormones, and family history of breast cancer, breast cancer risk significantly elevated in use of OC before 25 years old and before 1971. In stratified analysis, significantly higher risk were found in OC use before 25 years old and in duration of use less than one year among post-menopausal subjects. Our results support the notion that OC use in early life for younger women and in early calendar years increase breast cancer risk.

Oral contraceptives and cancer. A review of the evidence

The following review considers epidemiological data published from 1990 onwards on oral contraceptives (OCs) and the risk of cancers of the breast, cervix uteri, endometrium, ovary, liver and skin. In several studies, breast cancer risk was seen to be elevated among women who were current users of an OC, or had recently stopped using an OC, whereas there was no residual risk 5 or more years after stopping OC use. No interaction was observed between type of OC, or with any recognised risk factor for breast cancer, or time-factor, except for some potential excess risk for women who started OC use at a young age. Most studies have confirmed that OCs moderately increase the risk of cervical cancer, particularly in human papilloma virus (HPV)-positive women, thus suggesting that OCs may act as a promoter for HPV-induced carcinogenesis. Recent epidemiological studies have confirmed that combined OCs provide substantial protection against endometrial and ovarian cancers, and results suggest that such protection is long-lasting, and may persist for 15 years or more after stopping OC use. Most case-control studies have shown a relationship between OC use and hepatocellular carcinoma. However, data from cohort studies or analysis of vital statistics indicate that the public health impact of such an association is modest, if not negligible. No association was observed between combined OC use and the incidence of skin melanoma, or any other common skin neoplasm. In terms of clinical and public health implications, the most relevant points regarding OC use are: (i) recent data confirm that OCs confer presistent protection against ovarian cancer; and (ii) any increased risk of breast cancer in OC users is moderate and is restricted to current/recent users. This is reassuring for younger women, whose baseline risk of this disease is extremely low.

Oral contraceptives, menopausal estrogens, and the risk of breast cancer: a case-control study in Greece

In a hospital-based case-control study in Athens, we examined the association between the use of oral contraceptives and menopausal estrogens and the risk of breast cancer. Eight hundred and twenty patients with confirmed breast cancer were compared with 795 orthopedic patient controls and 753 healthy visitor controls, matched to the cases by age and interviewer. The data were modeled through logistic regression, controlling for demographic and reproductive variables. Odds ratio 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 elevated among ever-users of oral contraceptives, regardless of age at diagnosis of breast cancer, duration of oral contraceptive use or timing of use in relation to first full-term pregnancy. Among peri- and post-menopausal women who ever used menopausal estrogens, with never-users as the baseline, a statistically significant elevated odds ratio was found after adjusting for age at menopause.

Oral contraceptives and breast cancer: a cooperative Italian study

The relationship between oral contraceptives (OC) and breast-cancer risk was analysed using data from a case-control study conducted between June 1991 and February 1994 in 6 Italian centres on 1,991 patients below age 65 with histologically confirmed incident breast cancer and 1,899 controls admitted to hospital for a wide range of acute, non-neoplastic, non-hormone-related diseases. "Ever OC use" was reported by 18% of cases versus 14% of controls, corresponding to a multivariate odds ratio (OR) of 1.1 (95%) confidence interval, Cl 0.9 to 1.4). The ORs were 1.3 for use lasting < 1 year, 1.1 for 1 to 4 years, 0.9 for 5 to 8 years, and 1.2 for over 8 years. With reference to age at first use, there was some indication that the OR was elevated in women who had started use before age 30, but not in those starting at a later age. With reference to time since last OC use, the OR was above unity for women who had stopped for less than 10 years (1.6 for 1 to 4 years; 1.7 for 5 to 9 years), but the OR declined to unity for women who had stopped OC use for 10 years or longer. The OR for women who had stopped OC use for less than 10 years was consistently elevated across strata of selected covariates, and was directly related to the duration of use (OR 1.3 for < 5 years, 1.7, for > or = 5 years). In contrast, the OR was 0.6, for use lasting > or = 5 years in women who had stopped for 10 years or more. The elevated OR for women who had recently stopped OC use, together with the absence of association (or the suggestion of some protection) for those who had stopped for 10 years or more is consistent with the pattern of breast-cancer risk observed after a full-term pregnancy, and provides important reassurance on a public health level on the long-term impact of OCs on breast carcinogenesis.

Long-term benefits and risks of alternative methods of fertility control in the United States

A risk-benefit analysis of five alternative approaches to fertility control among US women over the age of 30 was performed: tubal ligation, vasectomy, intrauterine device, barrier method (condom), and combined oral contraceptives. Taken into account were age-specific probabilities of contraceptive failure, fecundability, spontaneous abortion, reproductive mortality (ectopic pregnancy, delivery, or induced abortion), life table mortality, and mortality from specific cancer sites (ovarian, endometrial, breast, and prostate) and cardiovascular disease. Relative to women using no contraceptive precautions, the use of any method of contraception between the ages of 30 and 50 was associated with net benefit in terms of averted deaths. However, when duration of observation was extended up to age 80, we predicted an excess of about 880 deaths from prostate cancer per 100,000 users of vasectomy. Other methods continued to be associated with net benefit, ranging from 130 to 360 deaths averted per 100,000 users. It was concluded that the non-reproductive risks and benefits of contraceptive methods continue to be relevant long after the reproductive years. The balance of risks and benefits may differ in other countries with different cause-specific and life table mortality rates.