Hormone replacement therapy and breast cancer morbidity, mortality and recurrence

Current Status of Combined Hormone Replacement Therapy in Clinical Practice

Approximately 20 million women worldwide use hormone replacement therapy (HRT). Formerly, it was thought to confer beneficial cardiac protection and reduce osteoporosis in addition to relieving the symptoms of menopause. However, many recent trials have contradicted these beliefs. The risk of breast cancer associated with HRT use has been well documented but underestimated. Many recent trials have reported higher than expected breast cancer incidence rates, particularly associated with combined HRT. Although it was believed estrogen conferred cardiac protection and reduced the incidence of myocardial ischemic events and cerebrovascular accidents, the more recent literature indicates that this is not true and that HRT users have a higher risk of cardiac and cerebral events. The role of HRT in clinical practice has been redefined. It is no longer an acceptable form of treatment for most women. The evidence indicates that the use of long-term HRT is no longer clinically justifiable.

Breast cancer and post-menopausal hormone therapy

From the introduction of post-menopausal hormone replacement therapy (HRT) there has been great concern that HRT could possibly increase the risk of breast cancer. Prolonged exposure to endogenous oestrogens undeniably increases the risk of breast cancer. Questions that are important and until now only partly answered, are the following. Are oestrogens tumour promoters, as they induce mitosis, lead to proliferation and, therefore, accelerated growth of clinically occult pre-existing tumours? In addition to this, are they genotoxic mutagenic carcinogens, or could they initiate tumours by way of accumulation of incessant DNA-replication damage mechanism? Opinions vary as to the effect of the addition of a progestogen. There is a multitude of different progestogens which could bind with differing affinity to progesterone receptor PR-A or PR-B, and which have different physiological functions via differential gene regulation. The action of a progestogen on the oestrogen-induced cellular mitotic activity could be synergistic or antagonistic (by different pathways: oestrogen receptor downregulation, activating of metabolic pathways within the breast or stimulation of apoptosis)? Over 60 observational studies and two randomized trials provide evidence that the small but significant increase in risk appears with long-term current post-menopausal hormone use. The addition of a progestogen does not decrease the risk as seen with oestrogens alone and might increase the risk further. It is not clear whether there is a difference in risk with sequentially combined versus continuously combined HRT. Many questions nevertheless still remain. Is the risk increase limited to lean women only? What about risk-modifying factors such as alcohol use and a positive family history for breast cancer? Are tumours detected under HRT less aggressive, is there a better prognosis and is the mortality not increased while morbidity is? And is HRT contraindicated for women with a positive family history for breast cancer or in those women who have been treated for breast cancer? And finally, are there alternative options for these women?

Effects of tibolone and hormone replacement therapy on the breast of cynomolgus monkeys

OBJECTIVE

To measure the effects of 2 years of treatment with tibolone on the breasts of cynomolgus macaques (Macaca fascicularis) in comparison with conventional hormone replacement therapy.

DESIGN

Ovariectomized cynomolgus macaques were randomized into five groups and treated for 2 years. Groups included controls (n = 31) and four drug treatments, including tibolone at 0.05 mg/kg (LoTIB, n = 30) or 0.2 mg/kg (HiTIB, n = 31), conjugated equine estrogens at 0.042 mg/kg (CEE, n = 28), or CEE + medroxyprogesterone acetate (MPA) at 0.167 mg/kg (CEE + MPA, n = 29). Endpoints included histologic, histomorphometric, and immunohistochemical assessment of the mammary gland.

RESULTS

Tibolone did not cause stimulation of the breast in contrast to distinct proliferative responses of the breast to CEE and CEE + MPA, as measured by increases in breast epithelial tissue area and expression of the proliferation marker Ki67 in breast epithelial cells. Tibolone at the higher dose increased progesterone receptor expression in the breast relative to controls, indicating partial estrogen-agonist activity, but without induction of proliferation. Progesterone receptor expression was also induced by CEE.

CONCLUSIONS

Tibolone may have an advantage over conventional hormone replacement therapy because it does not stimulate proliferation in the breast. This lack of mammotrophic effect may reflect a lower risk for promotion of breast cancer.

Comparative effects of tibolone and conjugated equine estrogens with and without medroxyprogesterone acetate on the reproductive tract of female cynomolgus monkeys

OBJECTIVE

To measure the effects of 2 years' treatment with tibolone on the reproductive tract of female monkeys (Macaca fascicularis) in comparison with conventional hormone replacement therapy.

DESIGN

Ovariectomized adult female monkeys were randomized for 2 years of treatment into five groups: controls (n = 31); tibolone at 0.05 mg/kg (LoTIB group; n = 30); tibolone at 0.2 mg/kg (HiTIB group; n = 31); conjugated equine estrogens (CEE) at 0.042 mg/kg (CEE group; n = 28); or CEE + medroxyprogesterone acetate (MPA) at 0.167 mg/kg (CEE + MPA group; n = 29). Endpoints included vaginal cytology; uterine weight; histopathologic evaluation of the uterus, vagina, and cervix; histomorphometry of the endometrium; and immunohistochemical detection of the proliferation marker Ki67 and progesterone receptor in endometrial tissue.

RESULTS

Endometrial atrophy was found in 29 of 30 and 23 of 31 animals in the LoTIB and HiTIB groups, respectively, compared with 0 of 28 and 11 of 29 in the CEE and CEE + MPA groups, respectively. All ovariectomized control animals had atrophic endometria. No complex or atypical hyperplasia was seen. Simple endometrial hyperplasia of a significant degree was seen in 3 of 31 HiTIB-treated animals, 1 of 30 LoTIB-treated animals, 26 of 28 CEE-treated animals, and 16 of 29 CEE + MPA-treated animals, and in none of the control animals. Marked simple endometrial hyperplasia and Ki-67 expression was induced by CEE and partially antagonized by MPA. LoTIB and HiTIB slightly increased endometrial thickness, whereas CEE and CEE + MPA induced a marked increase of 350% and 200%, respectively. Neither LoTIB nor HiTIB increased endometrial proliferation (Ki67 labeling) or induced vaginal keratinization. Endometrial bleeding was not seen in tibolone-treated animals but was present in 10 of 29 animals given CEE + MPA.

CONCLUSIONS

The effect of tibolone on the uterus and lower reproductive tract was minimal. The lack of a proliferative response of the endometrium to tibolone, coupled with the lower incidence of endometrial bleeding, suggests that tibolone may have advantages over CEE and CEE + MPA regarding endometrial safety and efficacy.

Use of the progestin challenge test in nonhuman primates (Macaca fascicularis)

OBJECTIVE

To determine whether the progestin challenge test (PCT) would provide a reliable, noninvasive indicator of endometrial stimulation in nonhuman primates. DESIGN; Randomized, 2x2, crossover study. SETTING; Nonhuman primates (Macaca fascicularis) in an academic research environment.

PATIENT(S)

Adult, surgically postmenopausal, female cynomolgous macaques (n = 27) were studied.

INTERVENTION(S)

Females were randomly assigned to receive estradiol (n = 14; 0.028 mg/kg body weight) or vehicle (n = 13) daily. All animals were administered two PCTs in a crossover study design using two doses (0.28 mg/kg or 0.56 mg/kg body weight) of medroxyprogesterone acetate (MPA).

MAIN OUTCOME MEASURE(S)

Incidence and severity of withdrawal bleeding and serum estradiol (E(2)) and progesterone (P(4)) levels were evaluated.

RESULT(S)

Estradiol treatment resulted in endometrial "withdrawal" bleeding in all but one instance. Females receiving daily doses of E(2) exhibited a significantly greater (P<.01) incidence, severity, and duration of withdrawal bleeding compared to control animals. Of the five positive responses observed in the control females, four occurred when the higher dose of MPA was administered.

CONCLUSION(S)

These results indicate that the PCT is a useful, noninvasive method for determining the presence of endometrial stimulation in nonhuman primates.

Effects of estrogens and hormone replacement therapy on breast cancer risk and on efficacy of breast cancer therapies

This review summarises preclinical and clinical data on effects of endogenous and exogenous estrogens on probability of breast cancer diagnosis, and on the course and efficacy of breast cancer therapies. The data indicate that higher endogenous estrogen exposure (e.g. pregnancy, early menarche and late menopause, estrogen levels in future breast cancer patients, obesity) or exogenous estrogens (oral contraceptives; hormone replacement therapies) may be associated with an increased probability of breast cancer diagnosis. However, there is little evidence that estrogens have deleterious effects on the course of breast cancer. Moreover, increased incidence of breast cancer diagnosis after prolonged hormone replacement therapy (HRT) use seems to be associated with clinically less advanced disease. In studies assessing both diagnosis and mortality, HRT is frequently associated with reduced mortality compared to never users. The interaction of progestagens and estrogens on the probability of breast cancer diagnosis is complex and dependent on type of progestagens and regimens employed. Efficacy of current treatment modalities for breast cancer (surgery, irradiation, adjuvant therapy or chemotherapy) is not negatively influenced by estrogens at concentrations considerably higher than those attained with current HRT preparations. Although it cannot be excluded that estrogens increase the probability of breast cancer diagnosis, available data fail to demonstrate that, once breast cancer has been diagnosed, estrogens worsen prognosis, accelerate the course of the disease, reduce survival or interfere with the management of breast cancer. It may therefore be concluded that the prevalent opinion that estrogens and estrogen treatment are deleterious for breast cancer, needs to be revisited. However, results of ongoing prospective, randomised clinical trials with different HRT regimens in healthy women or breast cancer survivors are needed to provide more definite conclusions about risks and benefits of HRT.

Hormone replacement therapy in women treated for gynaecological malignancy

Can we prescribe hormone replacement therapy (HRT) safely for women, with postmenopausal complaints who were treated for a gynaecological malignancy? Only three retrospective studies have investigated this issue in endometrial cancer patients. No recurrences or deaths occurred in these treated groups. However, the physician introduced bias through the selection of favourable groups. At present, combined estrogen and progestogen therapy is probably not contra-indicated in endometrial cancer stage I and probably also not in stage II, although so far there is only circumstantial evidence. Squamous cell cancers of the cervix, vulva, and vagina are unlikely to be influenced by HRT. In the only study available of women with ovarian cancer, < or = 50 years, estrogen replacement therapy did not have a negative influence on (disease-free) survival. According to the data currently available, no evidence exists that HRT adversely influences survival and overall survival after treatment for ovarian cancer. In general, adenocarcinomas of the cervix and leiomyosarcomas of the uterus may be managed such as the adenocarcinomas of the uterus. During the last 25 years, HRT has been shown to substantially reduce the risk of cardiovascular diseases, osteoporotic fractures and colon carcinoma. On the other hand there is a significant increase of the risk in breast cancer with prolonged use of > 5 years. Re-evaluation of the current view that HRT should no be given to women treated for a gynaecological malignancy is strongly warranted after evaluating the advantages and the disadvantages of HRT use in each individual patient. Long-term HRT in women treated for a gynaecological cancer must be based on the medical history of the individual patient (and her family).

Hormone replacement therapy: the perspectives for the 21st century

Nowadays different lines of evidence demonstrate the benefits of postmenopausal hormone replacement therapy (HRT). HRT is extremely effective in treating subjective symptoms and can really improve the quality of life of climacteric women. HRT and dementia: Estrogens are potentially relevant to the pathogenesis and treatment of Alzheimer's disease. The effects of different progestogens on cognitive functions and Alzheimer's disease are largely unknown. The prevention of Alzheimer disease might be a major indication to long term HRT. Large prospective, randomized trials will confirm these preliminary data. HRT and osteoporosis: HRT has been strongly correlated with higher bone mineral density and lower fracture incidence. Definite answers in terms of minimum effective dosages, timing and duration of HRT for fracture prevention are needed. HRT and cardiovascular disease: Different lines of evidence suggest that HRT can exert cardioprotective effects with substantial reduction of morbidity and mortality for cardiovascular disease in postmenopausal women. The effects and the role of progestogens in cardiovascular disease prevention are still debated. Prospective, randomized, controlled studies are needed to assess the impact of different HRT regimens on cardiovascular events. HRT and cancer: The major issue in the relationship between HRT and cancer is breast cancer. Long-term and current HRT use are followed by a slight, though significant increase in the risk of breast cancer. Progestogens can modify the cellular response of normal as well as cancer breasts. The possible protective effect of continuous progestogen addition is very interesting and needs further investigation. Alternative to classical HRT: Selective estrogen receptor modulators (SERM). SERMs such as raloxifene (RAL) are a new class of drugs that exert site specific estrogenic or antiestrogenic effects in different target tissues. RAL prevents bone loss and reduces serum cholesterol in postmenopausal women. In contrast to estrogen RAL does not stimulate breast or uterine tissues. In vitro RAL is highly effective at inhibiting the growth of estrogen-dependent breast adenocarcinoma cells. SERMs are expected to represent a major breakthrough for postmenopausal health.

CONCLUSION

HRT can be offered either as a preventive tool or as individualized care on the basis of personal needs. New therapeutic options like the SERMs will offer a substantial medical advancement for the treatment of postmenopausal women.

Postmenopausal hormone replacement therapy and cancer of the female genital tract and breast

Taking into account data from recent case-control and cohort studies, this review addresses anew the controversial issue of a possible relationship between hormone replacement therapy and an increased risk of female cancer. The adequate addition of a progestogen reduces considerably the significantly increased risk of endometrial cancer seen in current and in past long-term estrogen replacement therapy (ERT) users. However, a small risk increase might still be present with combined estrogen-progestogen replacement therapy (EPRT), and with low-dose continuous combined treatment. Whether long-term hormone replacement therapy increases the risk of breast cancer remains controversial. All four recent case-control studies report a small, marginally significant risk increase of about 20-30%, while two recent cohort studies are very reassuring. Sequential addition of a progestogen does not seem to influence breast cancer risk. Unfortunately, no data are available on the both practically and theoretically interesting option of continuous combined hormone replacement therapy. It can be concluded from the present data that hormone replacement therapy can be safely prescribed for periods of less than five years to women with climacteric symptoms. Short-term hormone replacement therapy for climacteric complaints in women who have been treated for the above-mentioned cancers should not be considered to be absolutely contraindicated as the available but scanty new data do not indicate any detrimental effect in such women.