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Use of Different Postmenopausal Hormone Therapies and Risk of Histology- and Hormone Receptor–Defined Invasive Breast Cancer

Agnès Fournier, Alban Fabre, Sylvie Mesrine, Marie-Christine Boutron-Ruault, Franco Berrino, Françoise Clavel-Chapelon

From the Institut National de la Santé et de la Recherche Médicale, Villejuif, France; Institut Gustave Roussy, Villejuif; EA4045, Universite Paris-Sud, Paris, France; and Istituto Nazionale Tumori, Department of Preventive and Predictive Medicine, Milan, Italy

Corresponding author: Françoise Clavel-Chapelon, PhD, Institut National de la Santé et de la Recherche Médicale, ERI 20, EA 4045, Institut Gustave Roussy, 94805 Villejuif Cedex, France; e-mail: clavel{at}igr.fr

	ABSTRACT

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Purpose We previously found that the risk of invasive breast cancer varied according to the progestagen component of combined postmenopausal hormone therapy (CHT): progesterone, dydrogesterone, or other progestagens. We conducted the present study to assess how these CHTs were associated with histology- and hormone receptor-defined breast cancer.

Patients and Methods We used data from the French E3N cohort study, with 80,391 postmenopausal women followed for a mean duration of 8.1 years; 2,265 histologically confirmed invasive breast cancers were identified through biennial self-administered questionnaires completed from 1990 to 2002. The relative risks (RRs) were estimated using Cox proportional hazards models.

Results Compared with postmenopausal hormone therapy (HT) never-use, ever-use of estrogen+progesterone was not significantly associated with the risk of any breast cancer subtype, but increasing duration of estrogen+progesterone was associated with increasing risks of lobular (P = .06) and estrogen receptor–positive/progesterone receptor–negative (ER+/PR–; P = .02). Estrogen+dydrogesterone was associated with a significant increase in risk of lobular carcinoma (RR, 1.7; 95% CI, 1.1 to 2.6). Estrogen+other progestagens was associated with significant increases in risk of ductal and lobular carcinomas (RR, 1.6; 95% CI, 1.3 to 1.8; and 2.0; 95% CI, 1.5 to 2.7, respectively), of ER+/PR+ and ER+/PR– carcinomas (RR, 1.8; 95% CI, 1.5 to 2.1; and 2.6; 95% CI, 1.9 to 3.5, respectively), but not of ER–/PR+ or ER–/PR– carcinomas (RR, 1.0; 95% CI, 0.5 to 2.1; and 1.4; 95% CI, 0.9 to 2.0, respectively).

Conclusion The increase in risk of breast cancer observed with the use of CHTs other than estrogen+progesterone and estrogen+dydrogesterone seems to apply preferentially to ER+ carcinomas, especially those ER+/PR–, and to affect both ductal and lobular carcinomas.

	INTRODUCTION

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The relationship between postmenopausal hormone therapy (HT) use and breast cancer risk has been investigated in many epidemiological studies whose results have led to the conclusion that estrogen-progestagen menopausal treatments (combined HTs [CHTs]) are carcinogenic to the human breast.¹ However, first, breast cancer is not a single entity, and it has been suggested that tumors with different histological or hormone receptor (estrogen receptor/progesterone receptor [ER/PR]) profiles are etiologically distinct.^2-4 Second, CHT is also not a single entity, since various doses, routes of administration, regimens and molecules used throughout the world may differentially affect breast cancer risk.^5,6

The mechanisms underlying the link observed between use of some HTs and breast cancer risk are not clear. Knowing how different HTs affect the risk of different types of breast cancer would provide a useful insight into the mechanisms by which HTs act in the carcinogenic process.

The particular interest in studying the relation between HT use and the risk of different histological types of breast cancer was stimulated by the observations that, in the United States, as the number of CHT users steadily increased, there was a marked increase in lobular but not ductal breast cancer incidence in women older than 50 years.⁷ Later ecological studies from the United States and Switzerland confirmed these observations.^8-11 Improved diagnostic techniques, increased diagnostic activity, and changes in criteria for pathological classification of lobular, ductal, as well as mixed ductal-lobular carcinomas may have played a role. However, epidemiological studies showed that CHT was associated with more elevated relative risks for lobular than for ductal cancer,^3,12-24 with only two exceptions.^19,20

Studies of the relationship between HT use and the risk of different receptor-defined breast cancers began to be carried out earlier,^{13,14,18-20,24-36} with the assumption that if HTs act through hormonal mechanisms, they should differentially affect the risk of cancers with different hormone receptor profiles. However, their results have been mixed.³⁷

In an earlier report we examined the relationship between different types of HT and breast cancer risk, considered as a single disease, in the French E3N cohort.⁶ We found that the risk was significantly lower with CHTs containing progesterone or dydrogesterone rather than other progestagens. We also observed a significant increase in risk with unopposed estrogens. We now examine whether the associations of these four types of HTs with breast cancer risk vary across different types of carcinomas, characterized by histological type and hormone receptor status.

	PATIENTS AND METHODS

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The E3N Cohort
E3N is a prospective cohort initiated in 1990 that consists of 98,995 French women born between 1925 and 1950 and insured by a health insurance plan covering mostly teachers. Participants, who gave written informed consent, completed biennial self-administered questionnaires addressing medical history, menopausal status, and a variety of lifestyle characteristics. The study was approved by the French National Commission for Data Protection and Privacy. E3N is the French component of the European Prospective Investigation into Cancer and Nutrition.³⁸

Identification of Breast Cancer Cases
Occurrence of cancer was self-reported, and a small number of cases were further identified from the insurance files or information on deaths. Pathology reports were obtained for 96% of the identified incident cases. Information on ER and PR status and histological type was extracted from these reports, and the invasive breast cancer cases were classified by histological type into ductal, lobular (including mixed ductal-lobular), or other; and by receptor status into ER+/PR+, ER+/PR–, ER–/PR+, ER–/PR–, or missing.

Identification of HT Use
Information on lifetime use of hormonal treatments was first recorded in the 1992 questionnaire. It requested the start date, brand names, and duration of each episode of hormone use. Women were given a booklet with color photographs listing the HTs marketed in France. The information was updated in each of the subsequent questionnaires sent in 1993, 1995, 1997, 2000, and 2002. The complete history of HT use was established using data from all the questionnaires. Unopposed HT consisted almost exclusively in estradiol compounds (1.3% of women ever-used conjugated equine estrogens). CHTs were classified as estrogen+progesterone, estrogen+dydrogesterone, or estrogen+other progestagens, following our previous finding that associations with breast cancer risk varied significantly across these different treatments.⁶

Population for Analysis and Follow-Up
Analysis was limited to postmenopausal women. Women were considered postmenopausal if they had had 12 consecutive months without menstrual periods (unless due to hysterectomy), had undergone bilateral oophorectomy, had ever used HT, or self-reported that they were postmenopausal. Age at menopause was defined as age at last menstrual period (unless due to hysterectomy and if the last menstrual period occurred before HT use); age at bilateral oophorectomy; or, in decreasing order of priority, self-reported age at menopause, age at start of HT, age at start of menopausal symptoms; or, if no information was available, age 47 years if menopause was artificial, and age 51 years otherwise, ages which corresponded to the median ages for artificial and natural menopause in the cohort, respectively.

Follow-up started either at the date of return of the baseline questionnaire for the women who were already postmenopausal, or at the date of menopause. Participants contributed person-years of follow-up until the date of cancer diagnosis, the date of the last completed questionnaire, or July 2002, whichever occurred first. Among the postmenopausal women (n = 87,936), we excluded those who had reported a cancer other than a basal cell carcinoma before the start of follow-up (n = 5,849), and women for whom no age at first HT use was available (n = 1,696). This left us with 80,391 women for analysis.

Statistical Analysis
Relative risks (RRs) for breast cancer were estimated using Cox proportional hazards models, with time since menopause as the time scale. For each specific type of breast cancer, separate models were used, and cases with an invasive cancer other than that under study were censored at the date of diagnosis. Cases with missing information on histological type or hormone receptor status were excluded from the corresponding analyses.

Potential confounding variables included in the models are indicated in the footnotes of the tables. When fewer than 5% of the values of a covariate were missing, they were replaced with the mode or the median values observed among the subjects with complete data.

HT use was included as a time-dependent variable, and the "healthy screenee" bias (due to mammograms usually being performed before HT is started) was dealt with by not considering women as exposed to HT until 1 year following the start of treatment; from the start of treatment and until one year had elapsed, they contributed person-years of follow-up to a separate category.³⁹ Women who changed HT during follow-up contributed person-years to the appropriate category until they changed, and thereafter to a "mixed use" category. Tests of homogeneity in the effect of a given HT on the risk of different types of breast cancer were based on Wald ² statistics.⁴⁰ All tests of statistical significance were two-sided, and significance was set at the .05 level. We performed all analyses using SAS software, version 9.1 (SAS Institute Inc, Cary, NC).

	RESULTS

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The average age at start of follow-up was 53.1 years (standard deviation [SD], 4.5; range, 40.0 to 66.1 years). A total of 2,355 primary invasive breast cancers were diagnosed during 653,125 person-years of follow-up (mean duration: 8.1 years; SD, 3.9). Those confirmed by pathology reports (n = 2,265) were included in the analyses of the risk of histology-defined cancer. Among them, 473 (20.9%) had missing information on combined ER and PR status, so that 1,792 cases were included in the analyses of the risk of receptor-defined breast cancer. Table 1 presents the distribution of joint ER and PR status and histological types of the cases.

The RRs of invasive breast cancer associated with HT ever-use did not vary significantly according to histological type (Table 3). Lobular breast cancer risk was significantly increased in women in the estrogen+dydrogesterone and estrogen+other progestagens groups, and the risk of ductal carcinoma was significantly increased in women in the estrogen+other progestagens group. When analyses were conducted separately for pure lobular and mixed ductal-lobular carcinomas, risks associated with HT use were still stronger for pure lobular than for ductal carcinomas, and even stronger for mixed ductal-lobular carcinomas (Table 3).

As age at menopause may be an important confounder in the analyses of the relationship between postmenopausal HT use and breast cancer risk,^42,43 we performed a sensitivity analysis restricted to women with the most precise age at menopause (ie, derived from information on age at last menstrual period, and/or self-reported age at menopause, n = 65,096). Our conclusions remained unchanged except that the differences between ductal and lobular breast cancer risks appeared more marked and reached statistical significance for estrogen+dydrogesterone (P = .03) and estrogen+other progestagens (P = .02).

	DISCUSSION

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We previously reported that the risk of invasive breast cancer, considered as a single disease, was significantly lower among users of estrogen+progesterone or users of estrogen+dydrogesterone than in users of estrogen+other progestagens.⁶ In the present analysis, the use of estrogen+progesterone was not significantly associated with the risk of any breast cancer subtype, though we found trends of increasing risks with increasing duration of use for lobular and ER+/PR– carcinomas. The RR associated with estrogen+dydrogesterone was significantly above one for lobular breast cancer. Use of estrogen+other progestagens was associated with increases in risk of both ductal and lobular carcinomas, and of ER+/PR+ and ER+/PR– carcinomas.

Widespread use of progesterone is a French peculiarity.⁴⁴ In our analyses, the "other progestagens" category encompasses a variety of progestins, the most used being promegestone and nomegestrol acetate.⁶

Progestagens may act on breast tissue through their interactions with steroid receptors, growth factors, and oncogenes, and with the cell-cycle and estrogen-metabolizing enzymes.⁴⁵ Because they differ in their chemical structure, metabolism, pharmacokinetics, and potency, it is reasonable to expect them to induce different responses in the breast.⁴⁶ However, in vitro data are conflicting, possibly because of variations in the experimental conditions.^45,47 Therefore, in vivo studies are of particular interest. Some studies found that the proliferation of breast epithelium increased during the luteal phase of the menstrual cycle.^48,49 However, in vivo, progesterone has been found to oppose the proliferative effects of estradiol on breast tissue of pre- and postmenopausal women.^50,51 The contrary has been found for medroxyprogesterone acetate (MPA) in postmenopausal women⁵² or surgically postmenopausal macaques.⁵³ In such a study on macaques, compared to placebo, estradiol+MPA resulted in significantly greater proliferation in lobular and ductal breast epithelium, while estradiol+micronized progesterone did not.⁵⁴ These studies support our findings suggesting that, when combined with an estrogen, progesterone may have a safer risk profile in the breast than some other progestagens. Our results regarding estrogen+dydrogesterone combinations are also plausible since the retroprogesterone dydrogesterone is the progestin with the chemical structure and pharmacologic effects closest to those of progesterone.

There is a strong suggestion in the literature that CHTs are more markedly related to risk of lobular than ductal carcinoma.²³ Our results do not contradict this observation, which is biologically plausible, as studies on PR– knockedout mice suggest that progesterone induces lobuloalveolar development, whereas estradiol stimulates ductal elongation and PR expression.⁵⁵ The lack of significant difference between ductal and lobular breast cancer risk in the estrogen+progesterone category may be due to a lack of statistical power.

Our findings that some CHTs primarily increase ER+ breast cancer risk is consistent with that of other epidemiological studies,^{13,18,20,30,33} with two exceptions.^24,36 In the Women's Health Initiative trial, the increase in risk in the CHT group did not appear to be limited to ER+ breast cancer,¹⁹ but the number of cases was quite small. Recently, parallel to the drop in HT use, incidence of breast cancer decreased in the United States in women who were 50 years of age or older; this decrease was confined to ER+ cancers.⁵⁶ In human breast ER+ tumorigenesis, estrogens directly drive cell proliferation.⁵⁷ Biologic and epidemiological data therefore suggest that some HTs exert direct and rapid hormonal effects on pre-existing ER+ breast cancers; this does not exclude that there may be a longer-term impact on ER– tumors. In our study, the low number of ER– tumors may have limited our power to detect moderate increases in ER– breast cancer risk.

We found that the use of some CHTs was more markedly associated with the risk of ER+/PR– than with the risk of ER+/PR+ carcinomas. However, in other studies that have investigated the relationship between CHTs and different receptor-defined breast cancers, two found increases in risk that tended to be more marked for ER+/PR+ than for ER+/PR– carcinomas,^18,20 and one found comparable increases in risk for both types of carcinoma.³⁶ Technical issues are unlikely to explain our results. Indeed, PR expression decreases after withdrawal of HT, and surgery is often performed several days after HT has been stopped; this decrease is however too weak to fully explain our results.⁵⁸ Progestins also induce a PR down-regulation,⁵⁹ but this down-regulation disappears 48 hours after the progestin withdrawal.⁶⁰ Absence of PR while ER is present may be due to overexpression of human epidermal growth factor receptor 2 (HER-2).⁶¹ One study, based on very small numbers, found that CHT was markedly associated with HER-2–amplified tumors.²⁴ Three other studies failed to find a significantly more frequent HER-2 overexpression in breast cancers diagnosed in HT users versus nonusers, but they too were based on small numbers of cases.^62-64 Absence of PR may also indicate high insulin-like growth factor (IGF), epidermal growth factor (EGF), and heregulin activities, which downregulate PR independently of ER status.⁶¹ Progestins such as MPA and promegestone upregulate IGF and EGF receptors⁶⁵; progesterone may also potentiate EGF pathway signaling in breast cancer cell lines,⁶⁶ perhaps to a lesser extent than other progestagens.⁶⁷ Progestagens might thus increase the potency of growth factors and hence preferentially affect the risk of ER+/PR– tumors.

The main strengths of our study have been discussed previously.⁶ They include the large population and regular updating of exposure during follow-up. Also, careful adjustment for various potential confounders decreased the probability that the differences we found on risk between different CHTs are explained by confounding. Lastly, there was no marked difference between users of the different types of CHTs regarding established breast cancer risk factors (data not shown).

Our study had several limitations. Firstly, data on hormone receptors were taken from various laboratories; ER and PR results were scored as positive or negative using techniques and cutoffs that may not have been standardized. Histological classification may have varied over time or between laboratories. However, any resulting outcome misclassification was unlikely to be related to the HT exposure, and would have tended to weaken and obscure any real differences in the association of HTs with different types of breast cancer. Another potential limitation is that the joint ER and PR status was not available for 20.9% of the histologically confirmed cases. However, we verified that HT use was not associated with hormone receptor status measurement, when the period of diagnosis was taken into account (before 1994, 1994 to 1996, 1997 or later, as introduced in the multivariate models presented in the current analysis; data not shown). Therefore, the lack of data on hormone receptor status for some breast cancer cases is unlikely to bias the estimates substantially. Finally, the relatively small numbers of cases in some subgroups (especially ER–/PR+ carcinomas, lobular carcinomas, or estrogen alone users) may have limited our ability to detect significant associations. We also had insufficient power to further split the "estrogen+other progestagens" category and present meaningful data according to the exact progestagen molecule used, which are numerous in France. Longer follow-up and additional cases will make it possible.

In conclusion, the present study suggests that CHTs, when related to breast cancer risk, preferentially affect the risk of ER+ carcinomas, and especially those ER+/PR–. Our study also suggests that the progestagen component of CHT may be of importance regarding breast cancer risk. Given the major public health implications associated with the use of postmenopausal HT, further research is needed on CHTs containing progesterone or dydrogesterone, which might be less harmful regarding breast cancer risk than those containing other progestagens.

	AUTHORS’ DISCLOSURES OF POTENTIAL CONFLICTS OF INTEREST

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Although all authors completed the disclosure declaration, the following author(s) indicated a financial or other interest that is relevant to the subject matter under consideration in this article. Certain relationships marked with a "U" are those for which no compensation was received; those relationships marked with a "C" were compensated. For a detailed description of the disclosure categories, or for more information about ASCO's conflict of interest policy, please refer to the Author Disclosure Declaration and the Disclosures of Potential Conflicts of Interest section in Information for Contributors.

Employment or Leadership Position: None Consultant or Advisory Role: None Stock Ownership: None Honoraria: Françoise Clavel-Chapelon, Besins, Effik Research Funding: None Expert Testimony: None Other Remuneration: None

	AUTHOR CONTRIBUTIONS

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Conception and design: Agnès Fournier, Françoise Clavel-Chapelon

Collection and assembly of data: Agnès Fournier, Françoise Clavel-Chapelon

Data analysis and interpretation: Agnès Fournier, Alban Fabre, Sylvie Mesrine, Marie-Christine Boutron-Ruault, Franco Berrino, Françoise Clavel-Chapelon

Manuscript writing: Agnès Fournier, Sylvie Mesrine, Franco Berrino, Françoise Clavel-Chapelon

Final approval of manuscript: Agnès Fournier, Alban Fabre, Sylvie Mesrine, Marie-Christine Boutron-Ruault, Franco Berrino, Françoise Clavel-Chapelon

	ACKNOWLEDGMENTS

 
We thank R. Chaït, M. Fangon, L. Hoang and M. Niravong for their technical assistance; the E3N group; and C. Holmes for assistance in English. The authors are also grateful to all participants for providing the data and to practitioners for providing pathology reports.

	NOTES

 
Supported by Mutuelle Générale de l’Education Nationale; European Community; French League against Cancer; Gustave Roussy Institute; French Institute of Health and Medical Research; 3M Company; several General Councils of France; Fondation pour la Recherche Médicale; Cancéropôle Région Ile-de-France; Direction Générale de la Santé; Agence Française de Sécurité Sanitaire des Produits de Santé.

Authors’ disclosures of potential conflicts of interest and author contributions are found at the end of this article.

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Submitted July 9, 2007; accepted November 27, 2007.

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