Abstract
Objectives:
To compare the effect of oral estradiol (E2) plus vaginal progesterone (P4) against placebo on endometrial thickness, endometrial biopsy pathology, cervical cytology and total cancer incidence among healthy postmenopausal women.
Study design:
This study is a sub-analysis of the Early versus Late Intervention Trial with Estradiol (ELITE), a randomized, double-blinded, placebo-controlled trial that previously demonstrated that hormone therapy (HT) was associated with less progression of subclinical atherosclerosis than placebo when therapy was initiated within 6 years after menopause but not when it was initiated 10 or more years after menopause. This sub-analysis included only ELITE participants with an intact uterus, who were randomized to either daily oral micronized 17-beta-E2 1 mg/day with 4% vaginal micronized P4 gel 45 mg/day for 10 days each month or placebo.
Main outcome measures:
Participants were evaluated at baseline and annually during a median follow-up of 4.8 years for endometrial thickness as determined by pelvic transvaginal ultrasound followed by an endometrial biopsy when indicated, and cervical cytology and cancer incidence.
Results:
Over up to 80 months of follow-up, participants randomized to oral E2 plus vaginal P4 had progressive and statistically significant increases in endometrial thickness (p<0.001), underwent more endometrial biopsies and had a higher rate of endometrial hyperplasia on endometrial biopsy compared with the placebo group. Due to the close follow-up of participants in the trial protocol, these abnormal findings were effectively treated.
Conclusion:
Our results suggest that 10 days of vaginal P4 45 mg/day is insufficient to completely oppose the effect of oral E2 1 mg/day on the endometrium. Further studies are needed to test alternative doses or frequencies of administration of vaginal P4 for adequate endometrial protection from E2 therapy among postmenopausal women.
ClinicalTrials.gov registration:
Keywords: vaginal progesterone, estradiol, postmenopause, endometrium, cervical cytology
Introduction
Data strongly suggest that estrogen replacement therapy is associated with beneficial effects on cardiovascular disease (CVD) when initiated within 10 years of the menopause [1, 2]. Growing evidence for the timing hypothesis supports the effects of postmenopausal estrogen therapy on atherosclerosis and CVD depending on the timing of the initiation of hormone therapy (HT) relative to menopause, age, or both [3–5]. Estrogen hormone replacement most effectively slows atherosclerosis when underlying vascular tissue is healthy and maintains up-regulated estrogen receptors [5–8].
Despite the importance of timing of HT initiation, there is concern that combined estrogen-progestogen therapy may attenuate estrogen’s beneficial effects on cardiovascular health [9–11]. It is likely that the effects of progestins are mediated through progesterone receptors that are present in the arterial wall as well as effecting down-regulation of estrogen receptors. To minimize any possible negative progestogen effect on estrogen receptors in the arterial wall while testing for a beneficial effect of estradiol (E2) effects on atherosclerosis progression, the Early versus Late Intervention Trial with Estradiol (ELITE) protocol selected a low-dose vaginal micronized P4, 10 days each month in women with a uterus. The purpose of this post-hoc analysis is to evaluate the effect of oral E2 plus vaginal P4 on endometrial thickness, endometrial biopsy results, cervical cytology and overall cancer incidence among healthy postmenopausal women during the ELITE follow-up.
Material and Methods
Study population
ELITE was a single center, randomized, double-blinded, placebo-controlled trial of HT administered to women stratified into one of 2 groups based on whether they were within 6 years of menopause or 10 years or more after menopause [12]. The trial was conducted from July 2005 to February 2013. Healthy postmenopausal women were randomly assigned to receive either HT or placebo according to time since menopause strata using a 1:1 ratio of stratified blocked randomization. The HT regimen for women with an intact uterus was daily oral micronized 17-beta-estradiol (oral E2) 1 mg/d with 4% vaginal micronized progesterone gel (vaginal P4) 45 mg/d for 10 days each month [13]. Women without an intact uterus were given 1 mg/d of oral micronized 17-beta-estradiol daily without the P4 or placebo and were not included in this analysis. The trial was approved by the Institutional Review Board of the University of Southern California. ELITE was registered at ClinicalTrials.gov (NCT00114517) and was funded by the National Institute on Aging, National Institutes of Health (R01AG024154). This analysis included ELITE participants with an intact uterus who underwent randomization to daily oral E2 plus vaginal P4 for 10 days each month compared with placebo for each product.
Gynecologic and cancer surveillance
Gynecological examinations among ELITE participants with a uterus included pelvic examination, pap smear and transvaginal uterine ultrasound (TVUS); these examinations were performed at baseline and every year during trial follow-up. An endometrial biopsy was obtained if endometrial thickness was > 5 mm on TVUS or if any postmenopausal bleeding was reported. The endometrial biopsy procedure was performed in a standard manner with a sterile Pipelle or similar uterine biopsy device; the biopsy tissue was sent for pathological examination at Labcorp, San Diego. Mammography was performed at baseline and annually at the USC Norris Breast Center. The occurrence of cancer was documented by medical records and pathology reports. Skin cancers were excluded from this analysis.
Outcomes
The outcomes of interest in this post hoc evaluation of oral E2 plus vaginal P4 were endometrial thickness measured by TVUS, need for endometrial biopsy and biopsy results, abnormal cervical cytology and cancer by site. Median follow up duration of ELITE was 4.8 years.
Statistical analysis
Based on the longitudinal annual data collection throughout the trial, more than 1 occurrence of outcome per participant was examined. The analysis was conducted in the intent to treat (ITT) and per protocol (PP) samples. ITT analysis included all participants with an intact uterus who were randomized to oral E2 plus vaginal P4 or placebo. The PP analysis censored follow-up observations for participants who had discontinued study vaginal P4 use for more than 30 days before the evaluated outcome.
Descriptive statistics were compared between treatment groups as mean (SD), t-test or median (IQR), Wilcoxon rank sum for continuous variables, and as frequency (%), chi square test for categorical variables. The median (range) of endometrial thickness was reported in active treatment versus placebo by years of follow-up. A mixed effects linear model evaluated whether log-transformed endometrial thickness differed by randomized treatment. Random effects were specified for participant-specific intercept (baseline endometrial thickness at 1-year visit). Time since randomization (year) was treated as a series of indicator variables, specifying the 1-year visit as the reference (the baseline measures at randomization to less than 1 year were excluded). Treatment by time since randomization (year) evaluated whether the effect of treatment versus placebo on endometrial thickness differed by years of follow-up.
The number of women with endometrial thickness > 5 mm, women undergoing endometrial biopsy, experiencing each endometrial biopsy outcome, abnormal cervical cytology, and all cancers (except skin cancer) were reported by treatment group. If a woman had more than one outcome, she was counted for each outcome category. The proportion of women in each treatment group experiencing each outcome and the difference of proportions between treatment groups with exact 95% confidence intervals are presented. A log rank test was used to compare the time until the first cancer (in months) by treatment group.
Results
Baseline demographics
From the total of 643 postmenopausal women randomized in ELITE, 526 women had an intact uterus at baseline. Among these women, 262 women were randomized to daily oral E2 plus vaginal P4 10 days per month and 264 women were randomized to double placebo. The mean (SD) age of women randomized to oral E2 plus vaginal P4 and placebo was similar (60.2 (6.5) years vs. 59.6 (6.7) years, respectively, p=0.26). The mean (SD) time since menopause was comparable between women randomized to oral E2 plus vaginal P4 and placebo (9.5 (7.1) years vs. 9.2 (6.6) years, respectively, p=0.56). Prior use of hormone therapy was reported in similar proportions in vaginal P4 (66.0%) and placebo (66.7%) groups (p=0.88).
Endometrial thickness
Baseline endometrial thickness was evaluated in 515 women among 526 with an intact uterus. Eleven women did not have baseline and post-randomization endometrial thickness evaluations (8 women ended trial participation before the 1 year follow up visit when the gynecological examination was scheduled, and endometrial thickness was not evaluable in 3 women) and were therefore not included in this analysis. Baseline endometrial thickness did not differ between women who were treated with oral E2 plus vaginal P4 and placebo. The median (IQR) baseline endometrial thickness was 1.7 (1.0–2.4) mm in the oral E2 plus vaginal P4 group and 1.5 (1.0–2.2) mm in the placebo group (Wilcoxon rank sum p=0.18).
The on-trial endometrial thickness increased from baseline among women treated with oral E2 plus vaginal P4 (Figure 1, Supplementary Table 1). Endometrial thickness over the trial follow-up was significantly greater among women receiving oral E2 plus vaginal P4 compared to placebo (p<0.001, Table 1). These findings were evident in both ITT and PP analyses. In the ITT population, the mean on-trial endometrial thickness was 1.86 (95%CI, 1.72, 2.05) mm greater in oral E2 plus vaginal P4 compared to placebo treated women; this difference was 1.97 (95%CI, 1.80, 2.18) mm in the PP population. The effect of HT on endometrial thickness did not differ by year of follow-up (time*treatment interaction p=0.17 for ITT population and p=0.29 for PP population).
Figure 1. Median (interquartile range) endometrial thickness by year and treatment group.
1A. Intention to treat population
1B. Per protocol population
Table 1.
Mean on-trial endometrial thickness (mm) by treatment group in intention to treat population and per protocol population
| Population | Least square mean (95% CI) | Time p | Treatment p | |
|---|---|---|---|---|
| Oral E2 plus Vaginal P4 | Placebo | |||
|
Intention to treat population (430 women N=2105) |
3.03 (2.83, 3.22) | 1.60 (1.52, 1.72) | 0.54 | <0.001 |
|
Per protocol population (366 women N=1619) |
3.13 (2.89,3.35) | 1.57 (1.46, 3.35) | 0.67 | <0.001 |
Least square means were estimated from a mixed effect linear model, including post-randomization values.
Time*Treatment interaction in ITT population p=0.17, PP population p=0.29
N=number of endometrial thickness measures, CI=confidence interval, E2=estradiol, P4=progesterone
Among the 515 women who had undergone transvaginal ultrasound to evaluate endometrial thickness, 153 (29.7%) had endometrial thickness > 5 mm at least once during follow-up. A higher proportion of women randomized to oral E2 plus vaginal P4 (115 women, 44.9%) than women randomized to placebo (38 women, 14.7%) had endometrial thickness >5mm on at least one follow-up TVUS (p<0.001).
Among 153 women with endometrial thickness > 5 mm, 78 women (50.9%) had more than one occurrence of endometrial thickness > 5 mm. A higher proportion of women randomized to oral E2 plus vaginal P4 (65 women, 56.5%) than women randomized to placebo (13 women, 34.2%) had more than one occurrence of endometrial thickness > 5mm (p=0.02).
Endometrial biopsy
In the ITT population, a total of 198 of 526 women (37.6%) had an endometrial biopsy at least once during the trial due to endometrial thickness > 5 mm on TVUS or postmenopausal bleeding. The proportion of women with at least one endometrial biopsy in the oral E2 plus vaginal P4 (134 women; 51.2%) treatment group was higher than placebo (64 women; 24.2%) with a treatment group difference of 27.0% (95%CI: 18.9%, 34.9%) (Table 2). Among the PP population, the proportion of women with at least one endometrial biopsy in the oral E2 plus vaginal P4 (111 women; 43.5%) treatment group was higher than placebo (52 women; 20.1%) with a treatment group difference of 23.4% (95%CI: 15.7%, 31.3%).
Table 2.
Endometrial biopsy findings by treatment group in intention to treat and per protocol populations
| Intention to treat population (198 women) | Per protocol population (163 women) | |||||
|---|---|---|---|---|---|---|
| Oral E2 plus Vaginal P4 (134 women) | Placebo (64 women) | Proportion Difference | Oral E2 plus Vaginal P4 (111 women) | Placebo (52 women) | Proportion Difference | |
| Endometrial malignancy or hyperplasia | 17, 12.7% (7.6%, 19.5%) | 2, 3.1% (0.4%, 10.8%) | 9.6% (2.5%, 16.6%) | 15, 13.5% (7.8%, 21.3%) | 1, 1.9% (0%, 10.3%) | 11.6% (4.2%, 19.0%) |
| Endometrial malignancy | 1, 0.7% (0%, 4.1%) | 2, 3.1% (0.4%, 10.8%) | −2.4% (−6.9%, 2.1%) | 0, 0% (0%, 3.3%) | 1, 1.9% (0%, 10.3%) | −1.9% (−5.7%, 1.8%) |
| Complex hyperplasia with atypia | 4, 3.0% (0.8%, 7.5%) | 0, 0% (0%, 5.6%) | 3.0% (0.1%, 5.9%) | 4, 3.6% (1.0%, 9.0%) | 0, 0% (0%, 6.8%) | 3.6% (0.1%, 7.1%) |
| Simple hyperplasia with atypia | 1, 0.7% (0%, 4.1%) | 0, 0% (0%, 5.6%) | 0.7% (−0.7%, 2.2%) | 1, 0.9% (0%, 4.9%) | 0, 0% (0%, 6.8%) | 0.9% (−0.9%, 2.7%) |
| Complex hyperplasia without atypia | 7, 5.2% (2.1%, 10.5%) | 0, 0% (0%, 5.6%) | 5.2% (1.5%, 9.0%) | 6, 5.4% (2.0%, 11.4%) | 0, 0% (0%, 6.8%) | 5.4% (1.2%, 9.6%) |
| Simple hyperplasia without atypia | 4, 3.0% (0.8%, 7.5%) | 0, 0% (0%, 5.6%) | 3.0% (0.1%, 5.9%) | 4, 3.6% (1.0%, 9.0%) | 0, 0% (0%, 6.8%) | 3.6% (0.1%, 7.1%) |
| Secretory endometrium | 2, 1.5% (0.2%, 5.3%) | 1, 1.6% (0%, 8.4%) | −0.1% (−3.7%, 3.6%) | 2, 1.8% (0.2%, 6.4%) | 1, 1.9% (0%, 10.3%) | −0.1% (−4.6%, 4.4%) |
| Proliferative endometrium | 96, 71.6% (63.2%, 79.1%) | 7, 10.9% (4.5%, 21.2%) | 60.7% (49.9%, 71.5%) | 79, 71.2% (61.8%, 79.4%) | 6, 11.5% (4.3%, 23.4%) | 59.6% (47.5%, 71.7%) |
| Atrophic endometrium | 37, 27.6% (20.2%, 36.0%) | 26, 40.6% (28.5%, 53.6%) | −13.0% (−27.2%, 1.2%) | 27, 24.3% (16.7%, 33.4%) | 22, 42.3% (28.7%, 56.8%) | −18.0% (−33.6%, −2.4%) |
| Other benign results | 65, 48.5% (39.8%, 57.3%) | 41, 64.1% (51.1%, 75.7%) | −15.6% (−30.0%, 1.1%) | 48, 43.2% (33.9%, 53.0%) | 32, 61.5% (47.0%, 74.7%) | −18.3% (−34.4%, −2.2%) |
Data reported as number of women, proportion, 95%confidence interval of proportion
E2=estradiol, P4=progesterone
Findings on endometrial biopsy were examined by treatment group. Among women having endometrial biopsy, the proportion of women with endometrial malignancy or hyperplasia was higher among women treated with oral E2 plus vaginal P4 (12.7%, 95% CI: 7.6%, 19.5%) compared with women treated with placebo (3.1%, 95% CI: 0.4%, 10.8%), with a treatment group difference of 9.6% (95%CI: 2.5%, 16.6%). Among endometrial biopsies, proportions of women showing complex hyperplasia with atypia, complex hyperplasia without atypia and simple hyperplasia without atypia were higher in women treated with oral E2 plus vaginal P4 compared to placebo. Proliferative endometrium was evident in a higher proportion of women treated with oral E2 plus vaginal P4 (71.6%, 95% CI: 63.2%, 79.1%) compared with women treated with placebo (10.9%, 95% CI: 4.5%, 21.2%), with a treatment group difference of 60.7% (95%CI: 49.9%, 71.5%) (Table 2). Similar endometrial biopsy results were found in the PP population.
Endometrial malignancy on endometrial biopsy that was subsequently diagnosed as endometrial cancer from a surgical specimen was reported in one woman receiving oral E2 plus vaginal P4 (well-differentiated endometrioid adenocarcinoma, FIGO grade 1) and in one woman receiving placebo (endometrial adenocarcinoma, endometrioid type, FIGO grade 1). One other woman receiving placebo who had an endometrial biopsy showing endometrial malignancy (scant detached high grade degenerated malignant cells) was diagnosed after surgery with advanced ovarian cancer without endometrial cancer on the surgical specimen.
Cervical cytology
Cervical cytology was evaluated in 517 women among 526 with an intact uterus. Nine women did not have cervical cytology reports (8 women ended trial participation before the 1 year follow up visit when the gynecological examination was scheduled, and one woman had vaginal bleeding so cervical cytology was not evaluable before dropping out of the study). A total of 96 women (18.6%) had abnormal cervical cytology on at least one examination during trial follow-up. Among women within the ITT population who had cervical cytology examination, the proportion of women with abnormal cervical cytology was similar between women receiving oral E2 plus vaginal P4 (51 women; 19.8%, 95% CI: 15.1%, 25.2%) and women receiving placebo (45 women; 17.4%, 95% CI: 13.0%, 22.5%) (Table 3). In the PP population having cervical cytology examination, the proportion with abnormal cervical cytology was also similar among women receiving oral E2 plus vaginal P4 (35 women; 13.6%, 95% CI: 9.6%, 18.4%) and women receiving placebo (36 women; 13.9%, 95% CI: 9.9%, 18.7%) (Table 3).
Table 3.
Cervical cytology findings by treatment group in intention to treat and per protocol populations
| Intention to treat population (517 women) | Per protocol population (517 women) | |||||
|---|---|---|---|---|---|---|
| Oral E2 plus Vaginal P4 (258 women) | Placebo (259 women) | Proportion Difference | Oral E2 plus Vaginal P4 (258 women) | Placebo (259 women) | Proportion Difference | |
| Total abnormal cervical cytology | 51, 19.8% (15.1%, 25.2%) | 45, 17.4% (13.0%, 22.5%) | 2.4% (−4.3%, 9.1%) | 35, 13.6% (9.6%, 18.4%) | 36, 13.9% (9.9%, 18.7%) | −0.3% (−6.2%, 5.6%) |
| Atypical squamous cells of undetermined significance | 37, 14.3% (10.3%, 19.2%) | 35, 13.5% (9.6%, 18.3%) | 0.8% (−5.1%, 6.8%) | 28, 10.8% (7.3%, 15.2%) | 28, 10.8% (7.3%, 15.2%) | 0% (−5.3%, 5.3%) |
| Atypical squamous cells cannot rule out high grade squamous intraepithelial cells | 3, 1.2% (0.2%, 3.4%) | 3, 1.2% (0.2%, 3.4%) | 0% (−1.8%, 1.8%) | 1, 0.4% (0%, 2.1%) | 3, 1.1% (0.2%, 3.3%) | −0.8% (−2.3%, 0.7%) |
| Low grade squamous intraepithelial lesion | 3, 1.2% (0.2%, 3.4%) | 0, 0% (0%, 1.4%) | 1.2% (−0.1%, 2.5%) | 2, 0.8, (0%, 2.8%) | 0, 0% (0%, 1.4%) | 0.7% (−0.3%, 1.8%) |
| High grade squamous intraepithelial lesion | 3, 1.2% (0.2%, 3.4%) | 6, 2.3% (0.9%, 5.0%) | −1.1% (−3.4%, 1.1%) | 1, 0.4% (0%, 2.1%) | 4, 1.5% (0.4%, 3.9%) | −1.1% (−2.8%, 0.5%) |
| Atypical endocervical glandular cells of undetermined significance | 9, 3.5% (1.6%, 6.5%) | 2, 0.8% (0%, 2.8%) | 2.7% (0.2%, 5.2%) | 7, 2.7% (1.1%, 5.5%) | 2, 0.8% (0%, 2.8%) | 1.9% (−0.3%, 4.2%) |
Data reported as number of women, proportion, 95%confidence interval of proportion
E2=estradiol, P4=progesterone
The number and proportion of women with each type of abnormal cervical cytology were similar between women treated with oral E2 plus vaginal P4 and placebo. The results were consistent in the ITT and PP populations. The most common abnormal squamous cervical cytology was atypical squamous cells of undetermined significance. A higher proportion of atypical endocervical glandular cells of undetermined significance was found in women treated with oral E2 plus vaginal P4 (3.5%, 95% CI: 1.6%, 6.5%) compared with placebo (0.8%, 95% CI: 0%, 2.8%), with a treatment group difference of 2.7% (95%CI: 0.2%, 5.2%) (Table 3).
Cancers
Total incident cancers did not differ in women treated with oral E2 plus vaginal P4 and placebo (Table 4). A total of 11 cancer diagnoses occurred among 11 (4.2%) women treated with oral E2 plus vaginal P4 and 13 cancer diagnoses occurred among 12 (4.5%) women treated with placebo. One placebo-treated woman was diagnosed with both uterine and lung cancer synchronously. The median time to first cancer diagnosis was 40 months among oral E2 plus vaginal P4 treated women and 17 months among placebo treated women (log rank test p=0.93).
Table 4.
Incident cancers by treatment group in intention to treat population
| Oral E2 plus Vaginal P4 (262 women) | Placebo (264 women) | Proportion Difference | |
|---|---|---|---|
| Total cancer (N women) | 11, 4.2% (2.1%, 7.4%) | 12, 4.5% (2.4%, 7.8%) | −0.3% (−3.8%, 3.1%) |
| Breast cancer | 6, 2.3% (0.8%, 4.9%) | 6, 2.3% (0.8%, 4.9%) | 0% (−2.5%, 2.5%) |
| Colorectal cancer | 3, 1.1% (0.2%, 3.3%) | 1, 0.3% (0%, 2.1%) | −0.8% (−0.7%, 2.3%) |
| Endometrial cancer | 2, 0.8% (0.1%, 2.7%) | 1, 0.4% (0%, 2.1%) | 0.4% (−0.9%, 1.7%) |
| Ovarian cancer | 0, 0% (0%, 1.4%) | 1, 0.4% (0%, 2.1%) | −0.4% (−1.1%, 0.4%) |
| Pancreatic cancer | 0, 0% (0%, 1.4%) | 1, 0.4% (0%, 2.1%) | −0.4% (−1.1%, 0.4%) |
| Stomach cancer | 0, 0% (0%, 1.4%) | 1, 0.4% (0%, 2.1%) | −0.4% (−1.1%, 0.4%) |
| Uterine cancer** | 0, 0% (0%, 1.4%) | 1, 0.4% (0%, 2.1%) | −0.4% (−1.1%, 0.4%) |
| Lung cancer** | 0, 0% (0%, 1.4%) | 1, 0.4% (0%, 2.1%) | −0.4% (−1.1%, 0.4%) |
| Months to first cancer diagnosis, median (IQR) | 40 (34.0–48.0) | 17 (4.5–32.0) | 0.93* |
Data reported as number of women, proportion, 95%confidence interval of proportion
E2=estradiol, P4=progesterone
Log rank test was used to compare the time until the first cancer (in months) by treatment group.
Uterine and lung cancer occurred synchronously within the same participant
The most common site of cancer was breast cancer that was diagnosed in 6 (2.3%) women treated with oral E2 vaginal P4 and 6 (2.3%) women treated with placebo. Endometrial cancer was diagnosed in 2 (0.8%) women treated with oral E2 plus vaginal P4 and 1 (0.4%) woman treated with placebo. All 3 women (2 receiving oral E2 plus vaginal P4 and 1 receiving placebo) who were eventually diagnosed with endometrial cancer had undergone an endometrial biopsy for thickened endometrium and/or postmenopausal bleeding. In the two women receiving oral E2 plus vaginal P4 diagnosed with endometrial cancer, one woman had endometrial malignancy (well-differentiated endometrioid adenocarcinoma, FIGO grade 1) and one woman had complex endometrial hyperplasia with atypia on their endometrial biopsy. One woman receiving placebo with endometrial malignancy (endometrial adenocarcinoma, endometrioid type, FIGO grade 1) on her endometrial biopsy was diagnosed with endometrial cancer after surgery.
Discussion
Our results showed that postmenopausal women taking oral E2 1 mg/d plus 4% vaginal P4 (45 mg/d) for 10 days per month had significantly higher endometrial thickness, underwent more endometrial biopsies and had a higher proportion of biopsies with endometrial hyperplasia compared to women taking placebo. These results were evaluated within a randomized clinical trial with a large sample among postmenopausal women who were continuously treated with oral E2 plus vaginal P4 when compared with placebo for an extended period (median follow-up 4.8 years). Previous studies of postmenopausal use of either oral or transdermal E2 opposed by different doses and regimens of vaginal P4 gel showed various results in endometrial thickness and endometrial hyperplasia compared to our study as discussed below.
A randomized open labeled multicenter clinical study among 127 postmenopausal women receiving either daily 0.625 mg/d CEE or 0.05 mg/d transdermal E2 with 4% (45 mg/d) and 8% (90 mg/d) vaginal P4 gel every other day for 6 doses/month evaluated endometrial biopsies after 3 months of treatment. Among 62 women receiving 4% vaginal P4 gel, 4 women (8%) had proliferative endometrium, simple or atypical hyperplasia; the remainder had progestational changes (secretory, oral contraceptive effect, negative, inactive, menstrual and atrophic) on endometrial biopsy. Among the 65 women receiving 8% vaginal P4 gel, all had progestational changes on endometrial biopsy and no women reported proliferative endometrium or endometrial hyperplasia [14].
An open label study among 69 postmenopausal women using daily oral E2 2 mg/d plus 4% vaginal P4 gel (45 mg/d) for 10 days per month or 4% vaginal P4 gel twice weekly evaluated endometrial thickness after 6–18 months of treatment. Mean endometrial thickness between baseline vs. after treatment was similar (5.1 vs. 4.9 mm among women receiving 4% vaginal P4 gel each day for 10 days per month and from 3.7 vs. 3.9 mm among women receiving 4% vaginal P4 gel twice weekly). The endometrial samples among women with bleeding and endometrial thickness > 5 mm showed no evidence of endometrial hyperplasia or cancer from either vaginal P4 gel regimens [15]. In contrast with our ELITE results showing increased endometrial thickness, this study showed similar endometrial thickness between baseline and at 6–18 months of treatment and did not report number of women with endometrial thickness > 5 mm. However, baseline endometrial thickness was far higher (3.7–5.1 mm) than in the ELITE study (1.7 mm); it is therefore difficult to directly compare findings between ELITE and this study.
Another prospective observational study of 35 postmenopausal women using transdermal E2 0.05 mg with 4% vaginal P4 gel (45 mg/d) twice weekly showed that at 1 year of follow up, endometrial thickness significantly increased from baseline (3.6 to 4.6 mm, p<0.0005). Most women (92.3%) had endometrial atrophy on the endometrial biopsy and the remainder showed decidualized endometrium [16]. As we found a consistent increased endometrial thickness at 1 year follow up in ELITE, the change in endometrial thickness from baseline to 1 year was more prominent (1.7 to 3.1 mm), possibly due to thinner baseline endometrium in our study. In comparison with these previous studies, ELITE used a different dose and regimen of HT, included a placebo comparison, had a far larger sample size and longer follow-up that provided the opportunity to detect long-term effects on the endometrium.
ELITE primary results supported the timing hypothesis that postmenopausal administration of oral E2 therapy was associated with less progression of subclinical atherosclerosis measured as common carotid intima media thickness (CIMT) compared to placebo when therapy was initiated within 6 years after the onset of menopause but not when it was initiated 10 or more years after menopause [12]. The use of 4% vaginal P4 10 days/month was designed to minimize any potential anti-estrogenic actions at the arterial wall level to clearly assess the potentially beneficial cardiovascular impact of oral E2 on CIMT in women with an intact uterus.
Although 4% vaginal P4 was generally well-tolerated, endometrial thickening was not completely inhibited with this dose, resulting in a gradual increase in endometrial thickness, requirement for endometrial biopsies and intervention for endometrial hyperplasia in 51.2% of the participants in the ITT group and 43.5% of the participants in the PP group. As part of the trial safety protocol, participants had very close follow-up and treatment for vaginal bleeding, abnormal endometrial biopsy and evaluation of abnormally thick endometrium. The protocol offered a high degree of safety for participants while suggesting that 4% vaginal P4 10 days/month is not be an ideal dose for routine long-term opposition of oral E2 1 mg/day.
Despite the lack of long-term data on an appropriate dose of vaginal P4 for endometrial protection among postmenopausal women, a large clinical trial reported adequate endometrial protection with oral P4 200 mg/day for 12 days/month. The Postmenopausal Estrogen/Progestin Interventions (PEPI) trial, a multicenter, randomized, double-masked, placebo-controlled trial reported a similar occurrence of endometrial hyperplasia over 3 years to placebo across 3 regimens of daily 0.625 mg conjugated equine estrogens (CEE) with medroxyprogesterone acetate (MPA) 2.5 mg/day, MPA 10 mg/day for 12 days/months or micronized P4 200 mg/day for 12 days/month [17]. Current evidence indicates that either continuous daily combined estrogen/progestogen treatment or daily estrogen with sequential progestogen has decreased endometrial hyperplasia and adenocarcinoma compared to no progestogen [18]. Although several studies have shown that continuous combined treatment was more effective than sequential treatment on endometrial protection, the effect is a function of dose and duration of the progestogen [19]. In our study, we found that 4% vaginal P4 10 days/month is not sufficient for endometrium protection, therefore, there is a need for further study for adequate regimens if vaginal P4 is to be used.
Strengths of this study include use of data from a randomized, double-blinded, placebo-controlled design with long-term longitudinal follow up. Although endometrial thickness was evaluated annually as part of the safety protocol, endometrial biopsy was performed only when clinically indicated to avoid unnecessary invasive procedures. Therefore, information on endometrial changes among all women due to vaginal P4 among all participants could not be determined.
The North American Menopause Society and the International Menopause Society require use of a progestogen to oppose the E2 effect on the endometrium among postmenopausal women with an intact uterus [20–22]. Different routes, doses and regimens of progestogen have varied effects on the endometrium, from no changes to increased endometrial thickness and atrophic to endometrial hyperplasia and endometrial cancer [23, 24]. Since vaginal P4 has a higher local endometrial effect than systemic P4 as determined by endometrial tissue P4 levels [25], vaginal P4 could potentially provide an alternative to systemic P4 with limited systemic effects [26]. However, given our data showing insufficient endometrial protection with the tested regimen, appropriate dose and regimen of vaginal P4 in conjunction with estrogen therapy requires further study to determine the optimal endometrial uterine protection. Our study emphasizes the importance of adequate exposure to progestogen to oppose the effect of estrogen on endometrial proliferation among postmenopausal women using hormone therapy.
Supplementary Material
Hilights.
This study evaluated the use of oral micronized 17-beta-estradiol 1 mg/day plus 4% vaginal micronized progesterone (P4) gel 45 mg/day for 10 days each month in postmenopausal women.
Ten days of vaginal P4 45 mg/day was insufficient to completely oppose the negative effect of oral E2 1 mg/day on the endometrium.
Alternative doses of vaginal P4 for adequate endometrial protection are needed.
Funding
The National Institute on Aging, National Institutes of Health (R01-AG024154 and R01-AG059690) provided grants to Dr. Howard N. Hodis.
Footnotes
Ethical approval
The trial was approved by the Institutional Review Board of the University of Southern California.
Provenance and peer review
This article was not commissioned and was externally peer reviewed.
Research data (data sharing and collaboration)
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