Effects of Estrogen Plus Progestin on Gynecologic Cancers and Associated Diagnostic Procedures:  The Women's Health Initiative Randomized Trial FREE

For years, there has been concern about possible associations of gynecologic malignancies with postmenopausal hormone therapy. The development of endometrial hyperplasia and endometrial cancer with unopposed estrogen is well recognized. To reduce or avoid this complication, progestin has been added,^1- 3 although results from randomized trials are extremely limited. These concerns have created a need for reasonable monitoring guidelines to follow-up women who experience vaginal bleeding while taking estrogen plus progestin.

The Women's Health Initiative (WHI) trial of estrogen plus progestin provides the first opportunity to examine possible associations of gynecologic malignancies with continuous combined postmenopausal hormone therapy in a large, randomized, double-blind, placebo-controlled setting. The trial was stopped early at the recommendation of the independent data and safety monitoring board on the basis of an increased risk of breast cancer supported by a summary measure of effects indicating risks exceeded benefits over an average of 5.2 years of follow-up. The initial report provided interim, locally adjudicated outcomes for endometrial cancer reported through April 30, 2002. This article summarizes centrally coded gynecologic cancer outcomes and related diagnostic procedures occurring prior to the announcement of the trial closure and participant unblinding (July 8, 2002).

Women were recruited at 40 clinical centers in the United States between September 1993 and October 1998, largely through direct mail. Eligibility required women to be between age 50 and 79 years, to be postmenopausal, and to provide written informed consent. Women were excluded if they had preexisting conditions that contraindicated use of hormones, had health conditions that suggested a predicted survival of less than 3 years, or were considered likely to be poor adherers to the study protocol. Only women who had not had a hysterectomy were considered for this trial. Eligible women were randomized in equal proportions using a stratified permuted block algorithm to either placebo or to 0.625 mg/d of conjugated equine estrogens plus 2.5 mg/d of medroxyprogesterone acetate, which was administered in a single tablet (Prempro, Wyeth, St Davids, Pa). Women who had a prior hysterectomy were randomized to a parallel trial of estrogen alone and are not included in these results. Study design details have been published.^4- 5

All WHI participants provided demographic, medical, reproductive, and family history information using self-administered questionnaires at baseline. Prior postmenopausal hormone use was ascertained through a structured interview asking women to describe the strength, schedule, and duration of each hormone preparation.

Endometrial Evaluation. For safety, endometrial biopsies were performed on every woman interested in the estrogen plus progestin trial prior to randomization. A 5% cohort of women was randomly selected at enrollment to undergo routine biopsies at follow-up years 3, 6, and 9. This cohort was intended to provide a valid comparison of the rates of endometrial pathological findings.

The WHI procedures called for endometrial biopsies to be performed by WHI trained and certified staff, who were licensed physicians, nurse practitioners, or physician assistants, using plastic endometrial suction curettes.^6- 7 Readings were obtained from local pathologists blinded to randomization assignment.

During follow-up, women with persistent or heavy bleeding were evaluated by the clinic gynecologist. If a nonroutine biopsy was indicated, study guidelines permitted the clinic gynecologist to then be unblinded to assist in further safety evaluation. Women selected for routine biopsies who had a biopsy in the last 12 months to evaluate bleeding problems were not required to repeat the procedure. When biopsies could not be accomplished, vaginal ultrasounds of the endometrium were performed.

At baseline, biopsy evidence of endometrial cancer, complex or adenomatous hyperplasia, or atypia disqualified women from participating, whereas findings of simple hyperplasia resulted in temporary exclusion pending resolution. During study follow-up, evidence of endometrial cancer, complex or adenomatous hyperplasia, or atypia required permanent discontinuation of study medicines. Simple hyperplasia identified during follow-up led to unblinding of the consulting gynecologist. Those participants assigned to placebo had study medications discontinued and were referred to their health care clinicians for further management. Those assigned to active therapy continued study medications supplemented with 20 mg/d of medroxyprogesterone acetate. In such women, the biopsy was repeated in 3 to 6 months.

An endometrial wall thickness of greater than 0.5 cm on vaginal ultrasound was considered evidence of an endometrial pathological finding⁸ and resulted in exclusion (at baseline) or discontinuation of study pills unless further evaluation ruled out malignancy.

Cervical Cytology. In all participants, Papanicolaou tests were performed at 3-year intervals in conjunction with routine pelvic examinations. Absent an a priori hypothesis of association between estrogen plus progestin and cervical cancer, these tests were performed by WHI staff as a courtesy, in conjunction with a required pelvic examination. Pathological analysis was obtained locally. During follow-up, the protocol was modified to accept Papanicolaou test results from a participant's health care clinician.

Abnormal test results were referred to the participant's health care clinician for further diagnostic evaluation and treatment, except when a change in use of study medicines was required.

Outcome ascertainment procedures have been described.⁵ Briefly, semiannual self-reports of new diagnoses were recorded and all associated medical records were obtained from local health care clinicians and classified by blinded physician adjudicators at each clinical center. The documents from all gynecologic cancer cases were forwarded to the WHI clinical coordinating center for centralized review by cancer coding specialists who were also blinded to randomization assignment and reported symptoms. Histological codes were based on the International Classification of Diseases for Oncology, 2nd Edition.⁹ Histological analysis was available from pathology reports for all ovarian and endometrial cancers. Stage and grade were coded using Surveillance, Epidemiology, and End Results guidelines.¹⁰ In this system, local-stage ovarian cancer refers to a tumor confined to the ovary with no tumor on the ovarian surface. A regional stage ovarian cancer represents a tumor that is present on the ovarian surface, or has evidence of spread to ascites, peritoneal washings, or other locations within the pelvis. Tumors that spread beyond the pelvis are considered distant stage. For endometrial cancers, local stage refers to cancers confined to the endometrium or myometrium/serosa. Regional-stage tumors have spread only to the pelvis, vagina, and/or the wall of the rectum or bladder. Information could not be obtained for ovarian cancer stage in 1 woman and ovarian cancer grade in 9 women. Because the number of primary peritoneal and fallopian tube cancers was small, these are reported together as other gynecologic cancers.

Tests for differences between groups in the distribution of pathological features of diseases, and rates and results of endometrial biopsies and Papanicolaou tests are based on Fisher exact tests. When a diagnostic procedure was performed multiple times for a woman, her most severe result is reported.

Cancer incidence rate comparisons are presented as hazard ratios (HRs) and 95% confidence intervals (CIs) from Cox proportional hazards models, stratified by age and randomization to the WHI dietary trial. Kaplan-Meier estimates of cumulative hazards are shown as 1 minus the disease-specific failure time estimates. For the primary results, adjusted 95% CIs are corrected for the 7 outcomes that contributed to the global index, which is consistent with our initial report.⁵ This adjustment may not completely account for the variability in these estimates, given the multiple outcomes that will be examined in this trial. No adjustments were made for multiple tests over time because these outcomes make only a minor contribution to early stopping considerations under WHI monitoring guidelines.¹¹

The primary analyses are based on the intent-to-treat principle. In the original design, women who had not had a hysterectomy were randomized to either unopposed estrogen, estrogen plus progestin, or placebo. After information from the Postmenopausal Estrogen/Progestin Interventions (PEPI) trial¹² indicated that it was not feasible to include an unopposed estrogen group in a long-term prevention study in women who had not had a hysterectomy, the estrogen group was closed and the 331 women previously randomized to unopposed estrogen were unblinded and switched to combined hormone therapy. Mean (SD) duration of exposure to unopposed estrogen in these women was 5.4 (3.1) months. When appropriate, analyses were performed separating out the women randomized during this phase to account for the exposure to unopposed estrogen. Several other sensitivity analyses were conducted. In per protocol analyses, events and follow-up time occurring more than 6 months after the participant became nonadherent to study medicines or initiated use of nonstudy hormones were censored. This analysis preserves the randomization assignment and attempts to limit the dilution of effects that nonadherence may entail. As treated analyses (attributing events to the woman's use of hormones, either study pills or those provided by her health care clinician, 6 months prior to the event) were also performed. Analyses censoring women at the time of surgical removal of the organs of interest (total hysterectomy for endometrial cancer and bilateral oophorectomy for ovarian cancer) were also conducted.

Potential effect modification with known gynecologic cancer risk factors was assessed in expanded proportional hazards models that included the designated risk factor and randomization assignment as main effects and the interaction between these. Participants with missing values were excluded only from the analyses using the relevant variables.

Throughout this article, we report unadjusted 2-sided P values to indicate the relative strength of evidence in these secondary analyses. Seventeen tests for interactions with selected baseline characteristics were examined and accordingly 1 test would be expected to be significant at the P = .05 level by chance alone. All analyses were performed using SAS statistical software (version 8.2, SAS Institute Inc, Cary, NC).

Many subject characteristics have been presented.⁵ Use of unopposed estrogen prior to enrollment was limited (11%), was generally of short duration (<5 years), and had not taken place recently (Table 1). Prior use of combined hormones was more common (18%) and also more recent.

The average follow-up time for this report is 5.6 years. At the time of our interim report, 42% of women randomized to estrogen plus progestin and 38% of women randomized to placebo had stopped taking their study medications.⁵ A total of 485 deaths (3%) occurred before July 8, 2002 (Figure 1).

The observed annual incidence rate of ovarian cancer was 34 per 100 000 person-years, somewhat lower than the population-based rate of 45 per 100 000 person-years reported by the Surveillance, Epidemiology, and End Results for women of this age distribution.¹³ The rate in the estrogen plus progestin group was elevated (20 vs 12; HR, 1.58; 95% CI, 0.77-3.24 [adjusted 95% CI, 0.59-4.23]), but not statistically significant. Limiting the analyses to invasive epithelial cancers did not change the results substantially (HR, 1.64; 95% CI, 0.78-3.45). The possibility of an increasing effect over time is suggested by the Kaplan-Meier estimates of cumulative hazards (Figure 2A) but likewise did not reach statistical significance. Controlling for family history of colorectal cancer, the only baseline risk factor exhibiting a noticeable degree of imbalance, produced a modest increase in the estimated effect (HR, 2.11; 95% CI, 0.96-4.60). No substantial changes were found in analyses conducted per protocol (HR, 1.51; 95% CI, 0.64-3.55), as treated (HR, 1.76; 95% CI, 0.87-3.55), or censoring at the time of bilateral oophorectomy (HR, 1.59; 95% CI, 0.78-3.25).

There was no evidence of a difference between treatment groups in the distribution of histological classes, morphological grade, or stage of disease at diagnosis (Table 2). No significant interactions were found with age, race/ethnicity, body mass index, family history of breast or ovarian cancer, family history of colorectal cancer, prior use of oral contraceptives, prior exposure to unopposed estrogen, or prior use of combined hormones. However, power for these tests was limited because the number of events was small. None of the women reporting a history of ovarian cancer at baseline experienced a new diagnosis of ovarian cancer. Ovarian cancer was the reported cause of death in 9 women taking estrogen plus progestin and 3 women taking placebo (HR, 2.70; 95% CI, 0.73-10.0).

The observed incidence rate of endometrial cancer was 62 per 100 000 person-years, which was also lower than the Surveillance, Epidemiology, and End Results rate of 83 per 100 000 person-years.¹³ A small, nonsignificant reduction in endometrial cancer risk was observed with estrogen plus progestin use (27 vs 31; HR, 0.81; 95% CI, 0.48-1.36 [adjusted 95% CI, 0.40-1.64]). A similar reduction was observed in cancers arising from the epithelium (all reported histological classes except stromal sarcoma and mixed mullerian) (23 vs 30; HR, 0.71; 95% CI, 0.41-1.22). Kaplan Meier estimates of the cumulative hazards reveal no differences in rates throughout follow-up beyond what could be readily explained by chance alone (Figure 2B). Three (0.9%) endometrial cancers were diagnosed among the 331 women originally randomized to estrogen alone compared with 3 (0.5%) cases among the 573 women randomized to combined hormones and 2 (0.4%) cases among the 522 women randomized to placebo during this same period. Removing these cases had a limited impact on the results (21 vs 29; HR, 0.72; 95% CI, 0.41-1.26). The per protocol and as treated analyses for endometrial cancer also did not yield important differences in overall findings (HR, 0.83; 95% CI, 0.42-1.64 and HR, 0.80; 95% CI, 0.45-1.43, respectively). Censoring at the time of hysterectomy provided a similar result (HR, 0.81; 95% CI, 0.49-1.36).

There was no evidence of a difference in the distributions of histological class, morphological grade, or stage at diagnosis of endometrial cancer by randomization assignment. No significant interactions were found with age, race/ethnicity, body mass index, hypertension, smoking status, pack-years of smoking, prior use of unopposed estrogen, or prior use of estrogen plus progestin. The possibility of an interaction with diabetes could not be tested because of the sparseness of these data. One death in the placebo group was attributed to endometrial cancer.

The numbers of borderline ovarian tumors (1 vs 3) and other gynecologic cancers (6 vs 1) were too small to provide meaningful comparisons. Using a combined outcome of invasive ovarian, primary peritoneal, and fallopian tube cancers resulted in an estimated HR that was slightly higher than invasive ovarian cancer alone (26 vs 13; HR, 1.92; 95% CI, 0.99-3.74). We note that one primary peritoneal cancer in the estrogen plus progestin group was detected by an ultrasound performed to evaluate the endometrium. One leiomyosarcoma of the uterus was also reported. No difference was detected in cervical cancer incidence (8 vs 5; HR, 1.44; 95% CI, 0.47-4.42).

Estrogen plus progestin reduced the percentage of unsuccessful biopsies relative to placebo in the cohort randomly selected for routine surveillance (21% vs 36%, P<.001), but no difference was observed in the distribution of findings among women with results available (P = .28) (Table 3). This comparison may be confounded by a higher proportion of women having multiple biopsies in the estrogen plus progestin group (47% vs 27%; P<.001) because it is impossible to accurately attribute biopsies in these women to those conducted in response to reports of bleeding vs those done routinely.

Among women selected for usual care, the fraction of women taking combined hormones and requiring diagnostic biopsies increased more than 5-fold over placebo (33% vs 6%; P<.001) and twice as many women required multiple biopsies (38% vs 17%; P<.001). Among women having successful biopsies, a higher proportion taking estrogen plus progestin had normal findings (85% vs 68%), reflecting increased bleeding not arising from malignant or premalignant lesions. While the proportion of biopsies yielding abnormal findings in women taking estrogen plus progestin was low, the proportion of women having these abnormalities in the estrogen plus progestin group was not reduced relative to placebo. More simple and adenomatous hyperplasias and atypias were found in the estrogen plus progestin group, although this increase may be an artifact of the higher biopsy rate.

More women in the estrogen plus progestin group were examined with ultrasound; the fraction with repeat ultrasounds was also elevated (Table 4). No significant differences were found in the endometrial findings of these examinations, but some small differences were noted in the proportion with other pelvic abnormalities.

Follow-up Papanicolaou test results were available for 94% of trial participants (Table 5). The distribution of findings varied significantly (P<.001) with the estrogen plus progestin group yielding slightly more mild dysplasia, low grade squamous intraepithelial lesions, or atypia than the placebo group (7.8% vs 5.5%) and fewer normal results (92% vs 94%).

During 5.6 years of follow-up, 111 women were diagnosed as having invasive gynecologic cancers (invasive ovarian, 32; endometrial, 58; nonendometrial uterine, 1; cervical, 13; and other gynecologic, 7). In women randomized to estrogen plus progestin, a nonsignificant 1.58-fold increase in ovarian cancer and a nonsignificant 19% reduction in endometrial cancer were observed, relative to placebo. Data for other gynecologic malignancies were too sparse to provide meaningful comparisons but were included for completeness. Women randomized to continuous combined hormones were subjected to more endometrial biopsies and vaginal ultrasounds and were more frequently found to have mild abnormalities in routine Papanicolaou tests.

In this trial, women taking estrogen plus progestin were diagnosed as having invasive ovarian cancer at a rate of 42 per 100 000 person-years, 15 per 100 000 person-years more than the placebo group rate. The possibility of an increase in ovarian cancer mortality was also noted. Many, but not all, observational studies have found a modest increased risk of ovarian cancer or ovarian cancer mortality associated with postmenopausal estrogen use,^14- 19 but few studies have reported results specifically on combined hormones. In a recently reported US cohort study,²⁰ an association was found with estrogen alone (odds ratio [OR], 1.6; 95% CI, 1.2-2.0) but not with combined hormones (OR, 1.1; 95% CI, 0.64-1.7), except possibly in women previously exposed to estrogen alone (OR, 1.5; 95% CI, 0.91-2.4). That study did not address the schedule of progestin use. A recent Swedish case-control study²¹ (the only currently available study known to distinguish between continuous combined hormone therapy and sequential progestin treatment) found an increased risk associated with use of unopposed estrogen (OR, 1.43; 95% CI, 1.02-2.00) and sequential preparations (OR, 1.54; 95% CI, 1.15-2.05), but not with use of continuous progestin regimens (OR, 1.02; 95% CI, 0.73-1.43). However, the majority of women in this latter study used a progestin derived from 19-nortestosterone rather than the 17-hydroxyprogesterone derivative medroxyprogesterone acetate used in the current trial.

While the etiologies of ovarian cancer are poorly understood, a role for estrogen and progestin is biologically plausible.²² For example, the gonadotropin hypothesis asserts that the many reproductive history risk factors having a modest association with ovarian cancer risk act indirectly by increasing exposure of the ovarian epithelium to estrogen^23- 24 and consequently to proliferation and malignant transformation.²⁵ Other hypotheses regarding inflammation of the ovarian epithelium²⁶ and retrograde bleeding²⁷ have been introduced and allow for an increased risk with hormones through an indirect pathway. The WHI data do not relate directly to the incessant ovulation hypothesis²⁸ because all participants were menopausal at entry.

Progestins have been hypothesized to have a favorable effect on ovarian cancer incidence²² based on generally consistent findings of lower risk associated with increasing parity and the use of oral contraceptives,²⁹ and on animal data describing a role for progestins in promoting apoptosis.³⁰ The current WHI trial cannot address this question directly, but the eventual comparison with the parallel trial of estrogen alone in women with prior hysterectomy may provide some insight. The WHI data suggest that the continuous combined estrogen and progestin preparation examined in the trial will have no role in ovarian cancer prevention.

In women taking estrogen plus progestin, the incidence of endometrial cancer during the 5.6 years of follow-up was 56 per 100 000 person-years or 13 fewer cases per 100 000 person-years than observed in women taking placebo. This difference cannot be distinguished from chance.

This is the first randomized, double-blind, placebo-controlled trial to demonstrate that endometrial cancer rates for women taking continuous combined hormones are similar to placebo group rates, indicating that progestin protects against the increased risk of endometrial cancer associated with unopposed estrogen. Several reasonably sized, randomized, placebo-controlled trials of combined hormones have reported a substantial reduction in the formation of endometrial hyperplasia, the presumed precursor to many endometrial carcinomas compared with women given estrogen-only therapy.^12,31- 32 The results of the present study are also consistent with one smaller randomized trial³³ and 3 observational studies reporting no increase in endometrial cancer risk associated with continuous combined estrogen plus progestin therapy of at least 3 years' duration.^1- 3

Uterine bleeding was a frequent adverse effect of this regimen, leading to much more frequent biopsies and ultrasounds in women taking combined hormones than taking placebo. This increase in bleeding and the gynecologic procedures needed to diagnose and resolve the ensuing concerns (including hysterectomy) continue to be a major drawback of combined hormone therapy, including continuous progestins.

The WHI data on cervical cancer are too limited to suggest there is any association between incidence and estrogen plus progestin therapy. The statistically significant increase in mild abnormalities detected on Papanicolaou tests is interesting and warrants further investigation.

The WHI estrogen plus progestin trial is the largest, randomized, double-blind, placebo-controlled trial of continuous combined hormones that has been conducted, yet some limitations must be acknowledged. The number of gynecologic cancers observed was small, yielding wide CIs for the overall effects and limited power to examine possible differential effects in disease subtypes or in subgroups of women. Use of community-based diagnoses rather than central reading of pathological specimens constrains our ability to provide detailed subclassification of disease. As gynecologic cancers were secondary end points of the trial, issues of multiple testing apply. Adjusted CIs are provided to suggest the additional conservatism needed in interpreting these results. The trial was stopped early, which limited the precision of these results and precluded the examination of longer-term exposure. Finally, this trial tested one means of administering a single hormone regimen. We do not know the extent to which these results apply to other postmenopausal hormones. The effects of estrogen alone will be examined in the parallel trial that is ongoing.

In assessing the overall merit of estrogen plus progestin therapy, the low rates of gynecologic cancers in the population and the limited precision in the estimated effects from this trial suggest that these results should not have an appreciable influence on most women's decision making when seeking relief for moderate to severe vasomotor symptoms, nor can they resolve questions of etiology. The possibility of an increased risk of ovarian cancer incidence and mortality remains worrisome, however, and needs confirmation. The increased need for diagnostic procedures in response to bleeding is an added burden and could reasonably affect a woman's decision to use these medicines. These data provide further support for the recently revised guidelines for the use of continuous combined estrogen plus progestin therapy.^34- 35