Long-term effects of tibolone on the endometrium as assessed by bleeding episodes, transvaginal scan and endometrial biopsy

Tissue selective estrogen complex (TSEC): a review

Objective:

This review describes historical development of selective estrogen receptor modulators (SERMs) and their combination with estrogens, termed a tissue selective estrogen complex (TSEC), and considers the potential for future TSEC development.

Methods:

This narrative review is based on literature identified on PubMed and the TSEC research and development experience of the authors.

Results:

SERMs have estrogenic and antiestrogenic effects in various tissues; however, no single agent has achieved an optimal balance of agonist and antagonist effects for the treatment of menopausal symptoms. Clinically, a number of SERMs protect against osteoporosis and breast cancer but can exacerbate vasomotor symptoms. Estrogens alleviate menopausal hot flushes and genitourinary symptoms as well as reduce bone loss, but the addition of a progestogen to menopausal hormone therapy to protect against endometrial cancer increases vaginal bleeding risk, breast tenderness, and potentially breast cancer. The search for an effective menopausal therapy with better tolerability led to the investigation of TSECs. Clinical development of a TSEC consisting of conjugated estrogens/bazedoxifene increased understanding of the importance of a careful consideration of the combination's components and their respective doses to balance safety and efficacy. Bazedoxifene is an estrogen receptor agonist in bone but an antagonist/degrader in the endometrium, which has contributed to its success as a TSEC component. Other oral TSEC combinations studied thus far have not demonstrated similar endometrial safety.

Conclusions:

Choice of SERM, selection of doses, and clinical trial data evaluating safety and efficacy are key to ensuring safety and adequate therapeutic effect of TSECs for addressing menopausal symptoms.

Clinical effects of tibolone in postmenopausal women after 5 years of tamoxifen therapy for breast cancer

OBJECTIVES

This observational, prospective, open, non-randomized study was designed to assess the safety and efficacy of tibolone for the treatment of climacteric symptoms in women with a history of breast cancer.

METHODS

A total of 156 women who had been treated for breast cancer and had received tamoxifen for 5 years participated in the study. One month after stopping tamoxifen, 52 women started taking tibolone while the rest served as untreated controls (n = 104). They were followed up (mean duration 61 months) for climacteric symptoms, cancer recurrence rate, breast density, endometrial thickness and adverse events.

RESULTS

There was no difference in cancer recurrence rate between the two groups. Breast density was not affected. Tibolone treatment alleviated climacteric symptoms and positively affected sexual problems. Endometrial thickness was not adversely affected by treatment and there was a low incidence of adverse events.

CONCLUSIONS

Tibolone was effective in the treatment of climacteric symptoms and well tolerated in a group of 52 women with a history of breast cancer. The cancer recurrence rate in the tibolone group was comparable to that of untreated controls. It should be noted that the limitations of the study design and the small number of events preclude any definitive conclusions about the effects of tibolone on breast cancer recurrence in general clinical practice. There were no breast-related adverse effects, and overall safety and tolerance were similar to those of the general population of postmenopausal women treated with tibolone.

Effects of tibolone metabolites on human endometrial cell lines in co-culture

In human endometrium, cell proliferation is regulated by ovarian steroids through heterotypic interactions between stromal and epithelial cells populating this tissue. The authors test the proliferative effects of tibolone and its metabolites using endometrial co-cultures that mimic the normal proliferative response to hormones. They found that both the Delta(4)-tibolone metabolite and the pure progestin ORG2058 counteract estradiol-driven epithelial cell proliferation. Surprisingly, the estrogen receptor binding 3-hydroxyl-metabolites of tibolone also counteracted estradiol-driven proliferation. Inhibition of proliferation by 3beta-OH-tibolone was abrogated by low doses of the progesterone receptor antagonist mifepristone. This suggests that 3beta-OH-tibolone is converted to a progestagenic metabolite. The authors found that the stromal cells used in the co-cultures express high levels of the ketosteroid dehydrogenase AKR1C2, which is able to oxidize 3beta-OH-tibolone back to tibolone. Thus, the unexpected progestagenic effect of 3beta-OH-tibolone in these co-cultures may be due to metabolic activity present in the stromal cells of the co-cultures.

Endometrial safety and bleeding with HRT: what's new?

There have been few additional published data concerning the effects of hormone replacement therapy (HRT) on the endometrium since December 2003. The Million Women Study has confirmed the known protective effect of progestogen with both sequential and continuous combined regimens, although also reporting an increased risk of endometrial cancer with tibolone. This finding has not been found in any other study previously or in the recently reported OPAL 3-year study. Bleeding during HRT remains an important issue for patient acceptability as well as physician concern about the implications. The incidence of bleeding is related to the dose of estrogen and the development of new low-dose therapies containing 0.5 mg oral estradiol, 0.3 mg oral conjugated equine estrogens or 14 microg estradiol daily by transdermal patch is associated with less bleeding and thus greater patient acceptability as well as minimal endometrial stimulation. Intrauterine delivery of progestogen is the most logical route of administration and provides a high level of progestogen directly to the endometrium, with good endometrial suppression and lower circulating levels than by other routes. The protective effect of progestogen on the endometrium has to be balanced against the apparent adverse effect on breast cancer risk.

Role of androgens, progestins and tibolone in the treatment of menopausal symptoms: a review of the clinical evidence

Estrogen-containing hormone therapy (HT) is the most widely prescribed and well-established treatment for menopausal symptoms. High quality evidence confirms that estrogen effectively treats hot flushes, night sweats and vaginal dryness. Progestins are combined with estrogen to prevent endometrial hyperplasia and are sometimes used alone for hot flushes, but are less effective than estrogen for this purpose. Data are conflicting regarding the role of androgens for improving libido and well-being. The synthetic steroid tibolone is widely used in Europe and Australasia and effectively treats hot flushes and vaginal dryness. Tibolone may improve libido more effectively than estrogen containing HT in some women. We summarize the data from studies addressing the efficacy, benefits, and risks of androgens, progestins and tibolone in the treatment of menopausal symptoms.

Tibolone histology of the endometrium and breast endpoints study: design of the trial and endometrial histology at baseline in postmenopausal women

OBJECTIVE

To address the endometrial safety of tibolone.

DESIGN

The Tibolone Histology of the Endometrium and Breast Endpoints Study (THEBES) is a randomized, double-blind, parallel-group trial of tibolone compared with continuous combined conjugated equine estrogen (CEE) and medroxyprogesterone acetate (MPA).

SETTING

Multi-country, multi-center ambulatory care setting.

PATIENT(S)

A total of 5,185 subjects were screened, and biopsies were obtained from 4,446 women.

INTERVENTION(S)

Participants were randomized in a 1:1:2 ratio, to tibolone (1.25 or 2.5 mg/d) or CEE-MPA.

MAIN OUTCOME MEASURE(S)

The one-sided 95% confidence intervals for the incidence of hyperplasia or cancer were evaluated for tibolone compared with CEE-MPA.

RESULT(S)

Endometrial biopsy results at baseline: atrophic (87.29%), inactive (0.25%), proliferative (6.12%), secretory (2.86%), menstrual type (0.40%), and hyperplasia (0.18%). Only subjects with atrophic or inactive endometrium were eligible for this study, and 3% of the women at screening either had no tissue (0.18%) or had an amount of tissue that was insufficient for diagnosis (2.72%). Three thousand two hundred forty postmenopausal women with a mean (+/-SD) age of 54.4 +/- 4.4 years and a mean time since menopause of 4.5 +/- 3.6 years were randomized.

CONCLUSION(S)

The Tibolone Histology of the Endometrium and Breast Endpoints Study is a prospective, randomized clinical trial, designed to provide evidence of the endometrial safety of tibolone compared with estrogen and progestogen. Screening endometrial histology shows a low prevalence of endometrial hyperplasia (0.18%) and no carcinoma.

The incidence and characteristics of uterine bleeding during postoperative GnRH agonist treatment combined with tibolone add-back therapy in endometriosis patients of reproductive age

OBJECTIVES

This study was undertaken to evaluate the incidence and the factors associated with uterine bleeding while taking GnRH agonist treatment combined with tibolone add-back therapy in endometriosis patients of reproductive age.

STUDY DESIGN

The medical records of 188 endometriosis (stages III-IV) patients of reproductive age receiving postoperative GnRH agonist treatment combined with tibolone add-back therapy for 6 months were reviewed. Clinical features were analyzed and compared between the two groups: Group A, patients without an episode of uterine bleeding (n=137) and Group B, patients that had experienced uterine bleeding (n=51).

RESULTS

Demographic profiles were not different in the two groups. The incidence of uterine bleeding was 27.1% and irregular spotting was the most frequent bleeding pattern. The proportion of patients who received ovarian surgery during pelviscopy was higher in Group B (p<0.05), but other clinical characteristics were not different between two groups.

CONCLUSIONS

The incidence of uterine bleeding was 27.1%. And, the proportion of patients who received ovarian surgery was higher in patients with uterine bleeding.

Effects of tibolone and continuous combined conjugated equine estrogen/medroxyprogesterone acetate on the endometrium and vaginal bleeding: results of the OPAL study

OBJECTIVES

The primary objective of the Osteoporosis Prevention and Arterial effects of tiboLone study was to compare the effect of tibolone and placebo on the progression of the common carotid artery intima-medial thickness; the common carotid artery intima-medial thickness and bone data will be presented elsewhere. A secondary objective was to assess the effects of tibolone (2.5 mg), continuous combined conjugated equine estrogen/medroxyprogesterone acetate [0.625/2.5 mg], and placebo on the endometrium and vaginal bleeding; these results are the subject of this report.

STUDY DESIGN

This 3-year, three-arm, international, randomized, double-blind, parallel group, placebo-controlled clinical trial enrolled 866 postmenopausal women (aged 45-79 years). The endometrium was assessed by annual transvaginal ultrasound scans and end-of-study biopsies (United States/United Kingdom centers only). Vaginal bleeding was recorded in daily diaries.

RESULTS

Endometrial thickness measured by transvaginal ultrasound scan increased slightly during the first year with tibolone and conjugated equine estrogen/medroxyprogesterone acetate, without any further progression. After 3 years, there were no significant differences between the tibolone, conjugated equine estrogen/medroxyprogesterone acetate, and placebo groups in the incidence of proliferation (1.4%, 4.8%, and 0%, respectively), endometrial hyperplasia (0% in all groups), or cancer (1, 0, and 1 case, respectively). During the first 3 months, bleeding/spotting rates were greater with conjugated equine estrogen/medroxyprogesterone acetate (48%) than with tibolone (18%; P < .001) or placebo (3%; P < .001). During 3 years of treatment, the incidence of bleeding/spotting was 66%, 48%, and 23% for conjugated equine estrogen/medroxyprogesterone acetate, tibolone, and placebo, respectively. The mean number of bleeding/spotting days was greater in the conjugated equine estrogen/medroxyprogesterone acetate than the tibolone or placebo groups (61, 28, and 7 days, respectively; P = .023 vs tibolone; P < .0001 vs placebo). The mean number of bleeding/spotting episodes was also greater in the conjugated equine estrogen/medroxyprogesterone acetate group (13 episodes) compared with the tibolone group (six episodes; P < .001) and placebo group (four episodes; P < .001). Vaginal bleeding was more commonly reported as an adverse event with conjugated equine estrogen/medroxyprogesterone acetate than tibolone (26.4% vs 10.8%, P < .0001) and as the reason for premature discontinuation (9% vs 2%, P = .001).

CONCLUSION

Compared with conjugated equine estrogen/medroxyprogesterone acetate, tibolone has a better tolerability profile with respect to vaginal bleeding but with a similar endometrial safety. These results reinforce the endometrial safety profile of tibolone.

[The benefits and risks of hormonal replacement therapy--an update]

Hormonal replacement therapy (HRT) with estrogens and gestagens has been used for more than 40 years in the treatment of menopausal complaints and can be considered an effective treatment for vaso-vegetative symptoms and urogenital atrophy. During the past few years many women and doctors have revised their opinions of HRT. The reasons for this change of view are mainly three large international studies: the Heart and Estrogen/Progestin Study, the Women's Health Initiative Study and the One Million Women Study. In this review we summarize the data from the most important studies and point out the actual status of the controversial discussion on the benefits and risks of HRT.

A 5-year study on the effect of hormone therapy, tibolone and raloxifene on vaginal bleeding and endometrial thickness

OBJECTIVES

To study the effect of standard and low-dose estrogen-progestin therapy (EPT), tibolone and raloxifene on the incidence of vaginal spotting/bleeding and endometrial thickness over a 5-year period.

METHODS

Seven hundred eighty-six postmenopausal women were studied in an open prospective design. Vaginal spotting/bleeding and endometrial thickness as assessed by transvaginal ultrasonography was compared between six categories of women over a 5-year period: three categories in women on continuous combined estrogen-progestin therapy, one category under tibolone, one category under raloxifene and one under no treatment. More specifically, women received tibolone 2.5 mg (N = 204), raloxifene HCl 60 mg (N = 137), conjugated equine estrogens 0.625 mg/medroxyprogesterone acetate 5mg (N = 122), 17beta-estradiol 2mg/norethisterone acetate 1mg (N = 58), 17beta-estradiol 1mg/norethisterone acetate 0.5mg (N = 76) or no therapy (controls, N = 189). Women with suspected endometrial pathology were referred for hysteroscopy.

RESULTS

Bleeding/spotting incidence was highest among standard dose EPT users (conjugated equine estrogens 0.625 mg/medroxyprogesterone acetate 5mg: 40.1%, 17beta-estradiol 2mg/norethisterone acetate 1mg: 44.8%, p < 0.001 compared to controls). Low-dose EPT associated with lower incidence of spotting/bleeding (34.1%). The incidence under tibolone and raloxifene was 22.5% and 2.9%, respectively, while 3.2% of women not receiving therapy reported vaginal spotting/bleeding. Mean endometrial thickness was not significantly affected in any of the groups studied. The drop-out rate due to spotting/bleeding was higher in the two higher dose EPT regimens. After logistic regression analysis, age at baseline was the only significant predictor of subsequent spotting/bleeding (b = -0.25, S.E. = 0.09, p = 0.006), while menopausal age and pre-treatment serum FSH had marginal significance.

CONCLUSIONS

EPT, tibolone and raloxifene do not appear to associate with significant changes in endometrial thickness in the majority of cases. The low-dose EPT regimen associated with a decreased incidence of unscheduled spotting/bleeding compared to the standard dose regimens. Tibolone expressed a favorable endometrial profile, as seen in its effect on unscheduled spotting/bleeding and mean endometrial thickness. Raloxifene associated with the lowest incidence in S/B and the lowest drop-out rate.s.

Treatment of menopausal symptoms: what shall we do now?

During the past few years, many women and doctors have revised their opinions of hormone replacement therapy (HRT) for menopausal symptoms, and a substantial number of individuals have discontinued its use because of concerns about side-effects. Numerous alternatives to HRT are promoted, and assessment of the quality of evidence about the safety and effectiveness of these compounds can be difficult. In this Review, we summarise the data from studies addressing the efficacy, risks, and benefits of frequently prescribed treatments, and offer evidence-based clinical guidelines for the management of menopausal symptoms. Although few comparative studies exist, oestrogen alone or combinations of oestrogen and progestagen are likely to be the most effective treatments for menopausal hot flushes and vaginal dryness. Tibolone is as effective as HRT, however, and might also improve libido. For those who wish to avoid hormonal treatments, there are few effective options. Selective serotonin reuptake inhibitors might be effective in the very short term (less than 12 weeks) and are well tolerated. There is not enough evidence that any of the complementary therapies available are any better than placebo for menopausal vasomotor symptoms, and few safety data exist.