Estrogen replacement therapy withdrawal and regression of metastatic breast cancer

Hormone Replacement Therapy in Breast Cancer Survivors

With recent emphasis toward early detection and with improved therapies, breast cancer is, increasingly, being diagnosed at a localised and curable stage More women, are therefore, entering menopause after successful treatment for breast cancer. In these former patients hormone replacement therapy (HRT) is generally avoided because of clinical concerns that oestrogen may reactivate the disease. Observational data on breast cancer survivors who have elected to use HRT do not indicate that it has a pronounced adverse effect. At the same time, data from prospective, randomised studies are not available to prove the safety of HRT in this population. Until such time, HRT should be considered with great caution in breast cancer survivors.

Occult breast tumor reservoir: biological properties and clinical significance

Small, occult, undiagnosed breast cancers are found at autopsy in up to 15.6 % of women dying from unrelated causes with an average of 7 % from eight separate studies. The mammographic detection threshold of breast tumors ranges from 0.88 to 1.66 cm in diameter based on the patient's age. Tumor growth rates, expressed as "effective doubling times," vary from 10 to >700 days. We previously reported two models, based on iterative analysis of these parameters, to describe the biologic behavior of undiagnosed, occult breast tumors. Our models facilitate interpretation of the Women's Health Initiative (WHI) and antiestrogen breast cancer prevention studies. A nude mouse xenograft model was used to validate our assumption that breast tumors grow in a log-linear fashion. We then used our previously reported occult tumor growth (OTG) and computer-simulated tumor growth models to analyze various clinical trial data. Parameters used in the OTG model included a 200-day effective doubling time, 7 % prevalence of occult tumors, and 1.16 cm detection threshold. These models had been validated by comparing predicted with observed incidence of breast cancer in eight different populations of women. Our model suggests that menopausal hormone therapy with estrogens plus a progestogen (E + P) in the WHI trial primarily promoted the growth of pre-existing, occult lesions and minimally initiated de novo tumors. We provide a potential explanation for the lack of an increase in breast cancer incidence in the subgroup of women in the WHI who had not received E + P prior to randomization. This result may have reflected a leftward skew in the distribution of occult tumor doublings and insufficient time for stimulated tumors to reach the detection threshold. Our model predicted that estrogen alone reduced the incidence of breast cancer as a result of apoptosis. Understanding of the biology of occult tumors suggests that breast cancer "prevention" with antiestrogens or aromatase inhibitors represents early treatment rather than a reduction in de novo tumor formation. Our models suggest that occult, undiagnosed tumors are prevalent, grow slowly, and are the biologic targets of a hormone therapy in menopausal women and of antiestrogen therapy for prevention.

Hormone replacement therapy and the risk of breast cancer

Hormone replacement therapy (HRT) is given to relieve the climacteric symptoms of menopause. Use of HRT reduced after a report from the Women's Health Initiative linked it to an increased risk of breast cancer. This association has been confirmed in several other studies, including the Million Women Study. The risk of breast cancer is greater for formulations that contain both estrogen and progesterone, compared with estrogen alone. The breast cancer risk associated with HRT is higher for estrogen receptor-positive cancers than for estrogen receptor-negative cancers, and for low-grade cancers compared with high-grade cancers. After cessation of HRT the increased risk of breast cancer dissipates within 2 years. The rapidity of the decline suggests that a proportion of breast cancers that are hormone dependent will regress if the hormonal stimulation is removed. In evaluating a woman who is considering HRT, factors that have been associated with an increased risk include the initiation of hormone use immediately after menopause, a lean body mass and high mammographic breast density.

Hormone replacement therapy and breast cancer

There is evidence that hormone replacement therapy (HRT) may both stimulate and inhibit breast cancers, giving rise to a spectrum of activities, which are frequently hard to understand. Here we summarise the evidence for these paradoxical effects and, given the current data, attempt to give an indication where it may or may not be appropriate to prescribe HRT.It is clear that administration of oestrogen-progestin (E-P) and oestrogen alone (E) HRT is sufficient to stimulate the growth of overt breast tumours in women since withdrawal of HRT results in reduction of proliferation of primary tumours and withdrawal responses in metastatic tumours. E-P, E including tibolone are associated with increased local and distant relapse when given after surgery for breast cancer. For women given HRT who do not have breast cancer the only large randomised trial (WHI) of E-P or E versus placebo has produced some expected and also paradoxical results. E-P increases breast cancer risk as previously shown in observational studies. Risk is increased, particularly in women known to be compliant. Conversely, E either has no effect or reduces breast cancer risk consistent with some but not all observational studies. Two observational studies report a decrease or at least no increase in risk when E-P or E are given after oophorectomy in young women with BRCA1/2 mutations. Early oophorectomy increases death rates from cardiovascular and other conditions and there is evidence that this may be reversed by the use of E post-oophorectomy. HRT may thus reduce the risk of breast cancer and other diseases (e.g., cardiovascular) in young women and increase or decrease them in older women.

Second consensus on medical treatment of metastatic breast cancer

The present consensus manuscript defines evidence-based recommendations for state-of-the-art treatment of metastatic breast cancer depending on disease-associated and biologic variables.

Immunoreactive estrogen receptor in breast tumor and adjacent tissue: association with clinicopathological characteristics in Indian population

BACKGROUND AND OBJECTIVES

Estrogen receptor (ER) status serves as an important prognostic marker in the management of breast cancer. The level of ER in breast tumor is different in different racial and ethnic groups. In the present study, we have compared the ER levels in breast tumor and adjacent normal tissue in Indian sub-population.

METHODS

Immunoreactive ER was measured by enzyme immunoassay in breast tumors (ERt) and adjacent area (ERa) derived from 45 breast cancer patients from North India. Clinical parameters like age, menopausal status, tumor stage, recurrence and treatment status were recorded.

RESULTS

A significant positive correlation was observed between the levels of ERt and ERa (r = 0.386, P = 0.009). While the ERt levels increased with advancing age (P = 0.087), the ERa levels did not change in different age groups. The ERt levels negatively correlated with tumor stage and recurrence (r = -0.263, P = 0.110 and r = -0.202, P = 0.189). A significant negative correlation was also observed between the ERa levels and tumor recurrence (r = -0.337, P = 0.025). Further, the ERt positivity was higher than the ERa positivity. The clinical characteristics like age, tumor stage, metastasis, recurrence, and treatment status did not correlate with ERt and ERa positivity.

CONCLUSIONS

The present study shows that the levels of ERt and ERa positively correlate and both ERt and ERa show negative correlation with tumor recurrence.

Therapy for Menopausal Symptoms During and After Treatment for Breast Cancer

Breast cancer is the most common newly diagnosed cancer in women. Life-time risk in the US is 1 in 8 (13.2%), in the UK it is 1 in 9 and in Australia it affects 1 in 11 women, of whom approximately 27% will be premenopausal at the time of their diagnosis. Many of these women will experience a sudden menopause as a result of chemotherapy, endocrine therapy or surgical interventions. For these women, the onset of menopausal symptoms is often sudden and severe. The management of such symptoms remains controversial. Women experiencing menopausal symptoms after breast cancer should be encouraged to avoid identifiable triggers for their symptoms and to consider lifestyle modification as a means of controlling those symptoms. When such measures fail, non-hormonal treatments may also be considered. These include clonidine, gabapentin and some antidepressants. Randomised trials have shown a significant difference in the symptom relief associated with various selective serotonin reuptake inhibitors and selective serotonin and noradrenaline (norepinephrine) reuptake inhibitors compared with placebo. Many women elect to use non-prescription complementary therapies to alleviate their menopausal symptoms. Systematic reviews of phytoestrogens have, however, failed to demonstrate significant relief of menopausal symptoms. More than 20 clinical trials have been conducted examining the relationship between postmenopausal hormone replacement therapy and breast cancer recurrence. The majority of these have been observational and have shown no increased risk of recurrence. However, the largest randomised trial that has thus far been conducted was recently halted because of a reported increase in the risk of recurrence amongst users of hormone replacement therapy. Tibolone, a selective tissue estrogen activity regulator, is a compound that exerts clinical effects both by receptor-mediated actions and tissue selective enzyme inhibition, and has been shown in preclinical studies to have different effects to estrogen on the breast. Although tibolone may prove safer than estrogen for long-term use in breast cancer survivors, the results of a large randomised trial are awaited to confirm this.The decision on how best to manage menopausal symptoms must thus be made on an individual basis and after thorough discussion and evaluation of the risks and benefits of each potential intervention.

Raloxifene rebound regression

The first case of clinical remission of metastatic breast after the withdrawal of raloxifene is reported. A postmenopausal woman was treated for stage II breast cancer with a modified radical mastectomy and adjuvant cyclophosphamide, doxorubicin, and 5-flurouracil followed by tamoxifen for 5 years. One year following the cessation of tamoxifen, osteopenia was noted and raloxifene was begun. Two years following the start of raloxifene, supraclavicular adenopathy and lung metastases developed, which regressed after discontinuation of raloxifene. Although raloxifene is not frequently given to women with previous breast cancer, increasing use in osteopenic women may lead to cancer developing in these raloxifene-treated women; this despite the major reduction in the incidence of breast cancer in raloxifene-treated versus placebo-treated women. A clinically significant response to the withdrawal of a hormone, used either for the treatment of breast cancer or for some other reason, is not a rare event, and the therapeutic usefulness of observation only for a rebound regression is a frequently overlooked strategy in the treatment of breast cancer.

Short-term biologic response to withdrawal of hormone replacement therapy in patients with invasive breast carcinoma

BACKGROUND

The biologic effect of continuing hormone replacement therapy (HRT) after a diagnosis of breast carcinoma is unclear. The goal of rhe current study was to determine the short-term effect of HRT withdrawal on invasive breast carcinoma using biologic surrogate markers of tumor response.

METHODS

The study was performed between 1996 and 2000 and comprised 140 women who had been using HRT at the time of breast carcinoma diagnosis by core needle biopsy. The breast tumors were removed a median of 17 days later (range, 2-31 days). Of these women, 125 women stopped HRT at the time of core needle biopsy and 15 continued to receive HRT until surgery. In addition, 55 women with breast carcinoma from the same time period, who were not receiving HRT at diagnosis, were studied. Changes in expression of Ki-67 (a measure of epithelial cell proliferation), progesterone receptor (PR), p27KIP-1 (a cyclin-dependent kinase inhibitor), and cyclin D1 (a cell cycle-related protein) were determined by immunohistochemistry on paired sections of the core needle biopsy and surgical specimens from each patient.

RESULTS

In women who stopped HRT, a significant decrease in Ki-67 expression was observed between core needle biopsy and surgery in estrogen receptor (ER)-positive (n = 106; P < 0.001), but not in ER-negative tumors (n = 19; P = 0.58), with an associated reduction in PR (P < 0.001) and cyclin D1 expression (P < 0.001) and an increase in p27KIP-1 (P = 0.03). These changes in Ki-67 and PR expression occurred irrespective of c-erb-B2 status. No change was observed in any parameter in the other groups of patients.

CONCLUSIONS

ER-positive invasive breast carcinomas demonstrated a favorable biologic response to withdrawal of HRT. Therefore, HRT should be stopped at the time of diagnosis and was subsequently contraindicated.

Hormone-replacement therapy and breast cancer

Hormone-replacement therapy (HRT) has been available for many years, but the important question of its place in development and progression of breast cancer remains controversial; provision of reliable risk estimates has been hampered by a lack of controlled data. Observational evidence suggests that the risk of breast cancer may be increased only if HRT is used long term (ie, for longer than 10 years) and that the risk falls when use ceases. Systematic bias and the lack of adequately powered studies prevent any firm clinical recommendations about the prescription of differing HRT regimens and risk, or the effect of HRT on breast-cancer proliferation and mortality. This review aims to summarise current clinical data, justifying the need for prospective controlled trials in healthy women as well as those at higher risk of breast cancer or with a personal history of the disease.

Estrogen as therapy for breast cancer

High-dose estrogen was generally considered the endocrine therapy of choice for postmenopausal women with breast cancer prior to the introduction of tamoxifen. Subsequently, the use of estrogen was largely abandoned. Recent clinical trial data have shown clinically meaningful efficacy for high-dose estrogen even in patients with extensive prior endocrine therapy. Preclinical research has demonstrated that the estrogen dose-response curve for breast cancer cells can be shifted by modification of the estrogen environment. Clinical and laboratory data together provide the basis for developing testable hypotheses of management strategies, with the potential of increasing the value of endocrine therapy in women with breast cancer.

Hormone replacement in women with a history of breast cancer

Estrogen used alone (estrogen replacement therapy [ERT]) or with the addition of progesterone (hormone replacement therapy [HRT]) is known to be effective in reducing menopausal symptoms including hot flashes, vaginal dryness and urinary symptoms. It has been traditionally contraindicated, however, in women with a previous diagnosis of breast cancer because of fear that it may increase the risk of recurrence. There are considerable basic scientific data but little methodologically strong observational data and none from randomized studies concerning the use of ERT in women with a prior diagnosis of breast cancer. From our knowledge of the physiology of breast cancer, however, estrogen and/or progestational agents should be used with caution in women with a previous diagnosis of breast cancer. There are currently many alternatives to ERT/HRT in the prevention of menopausal symptoms such as vitamin E, clonidine and selective serotonin reuptake inhibitor antidepressants such as venlafaxine. There are also a variety of other approaches to the prevention of osteoporosis and cardiovascular disease including bisphosphonates, diet, and exercise; and diet, exercise, and statins, respectively. Other suggested beneficial effects of estrogen such as colon cancer prevention can be approached by the use of aspirin or the non-steroidals. Several trials of ERT/HRT used for 2 years versus no therapy in menopausal women with a previous diagnosis of breast cancer are ongoing in Europe and Britain, and should give us stronger data as to the role of HRT in this setting.

Prognosis of breast cancers detected in women receiving hormone replacement therapy

OBJECTIVE

To determine the influence of hormone replacement therapy (HRT) on various prognostic factors of breast cancer (BC).

METHODS

A multi-centre case-control study was conducted, in which a comparison was made of the differences between various histological and biological clinical variables of BC detected in 121 women undergoing HRT at the time of diagnosis, and those cancers detected in 121 women of similar age not undergoing HRT. The variables were also analysed in function of the type of HRT and the length of time treated.

RESULTS

The tumours detected in patients receiving HRT presented significantly lower tumoural stages, a lower degree of affected axillary lymph node dissemination, and a greater percentage of well-differentiated tumours and positive estrogen receptors than those detected in women not under HRT. Most of these results due principally to those patients who were undergoing

CONCLUSIONS

Although the better prognosis of tumours detected in women receiving HRT may be due largely to their diagnosis at earlier stages, there is an increasing body of data leading one to think that these tumours present certain histological and biological characteristics that make such cancers less aggressive.

The role of hormone replacement therapy in women with a previous diagnosis of breast cancer and a review of possible alternatives

Estrogen replacement therapy either with (HRT) or without (ERT) accompanying progesterone is routinely offered to well women at the time of menopause, in order to relieve vasomotor symptoms, (hot flashes), reduce urogenital atrophy and reduce the risks of cardiovascular disease, osteoporosis and perhaps colon cancer and Alzheimer's disease. It is generally felt however, that women with a previous diagnosis of breast cancer are not suitable candidates for such therapy since either estrogen or progesterone may be associated with an increased risk of cancer recurrence. There are however, a variety of approaches to menopausal therapy in such women. A careful history must first be taken in order to identify the symptoms or conditions of concern. Vasomotor symptoms can be reduced by the use of other medications such as the antidepressant venlafaxine (Effexor). Estring, a vaginal estrogen ring can be used to reduce genitourinary symptoms, with little systemic estrogen absorption. Osteoporosis can be prevented or treated with calcium supplements, exercise, improved diet, bisphosphonates and/or selective estrogen receptor modulators (SERMs) while cardiovascular risk can be reduced by diet and exercise, as well as the appropriate use of lipid lowering and antihypertensive medications.

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 and breast cancer

There is considerable evidence that the risk of breast cancer is related to ovarian function. However, the effect of postmenopausal hormone replacement therapy (HRT) on breast cancer risk continues to be debated in the absence of data from randomised controlled trials. Observational studies suggest that HRT probably promotes the growth of pre-existing breast cancers rather than initiating malignant transformation of breast epithelial cells but without exerting an obviously detrimental effect on disease-specific mortality. The controversy surrounding HRT and breast cancer has become additionally more complex as a result of the dilemma faced by clinicians advising women rendered oestrogen-deficient by breast cancer therapy. Whilst HRT is currently contra-indicated due to theoretical concerns that it will promote disease recurrence, its increasing, ad hoc prescription to symptomatic breast cancer patients has not been associated with an increase in disease recurrence. Large-scale randomised trials of HRT in healthy women and breast cancer survivors are now ongoing but it will be some years before useful clinical information becomes available. Until then, the limitations and biases implicit as a result of the design of observational studies must be borne in mind when interpreting such studies.

Special considerations in breast cancer risk and survival

Experimental and clinical evidence suggests that breast neoplasia appears to be a hormone-dependent process that may also be influenced by dietary factors in many women. Conflicting reports on the relationship between exogenous hormones and the development, progression, and recurrence of breast cancer are critically examined in this report. The absolute breast cancer risk associated with either hormone replacement therapy or oral contraceptive use has not been clearly defined. Data from some large prospective studies have actually documented lower mortality rates for women taking hormone replacement compared with those for women who did not have hormone replacement therapy. In this regard, age, duration of use, and preexisting breast cancer risk factors must be taken into account. Although the results of two major prospective clinical trials addressing the role of timing of surgery within the menstrual cycle are forthcoming, the majority of studies have found no consistent association between timing of surgery and breast cancer survival. Recently reported prospective randomized data showing that selective-estrogen-receptor-modulators can act as effective chemoprevention agents in women at increased risk for breast cancer development are presented. Finally, information regarding the effect of dietary manipulation on breast cancer risk and survival is reviewed.

Iatrogenic acute estrogen deficiency and psychiatric syndromes in breast cancer patients

The change of estrogen function, represented by amenorrhea or hot flashes, that results from breast cancer treatment may increase the risk of major depressive disorder in those women undergoing treatment for breast cancer. This pilot study describes the course of menopausal symptoms and the incidence of depression in 21 patients who were likely to become acutely estrogen deficient during treatment for breast cancer. These included women who lost menses during chemotherapy, who suddenly stopped estrogen replacement therapy (ERT), or who started tamoxifen. Eight patients (38%) developed major depressive disorder, the majority within 6 months of starting treatment. Twenty patients (95%) had dysphoria and/or insomnia. Fourteen patients (66%) had hot flashes. While this is only pilot data, these data suggest that breast cancer patients whose treatment precipitates menopausal symptoms should be targeted for diagnosis of depression and treated if diagnosed.

Hormone replacement therapy and breast cancer

The use of hormone replacement therapy by postmenopausal women with a history of breast cancer is a subject of considerable controversy. There are no scientific studies that have appropriately examined the issue, and current practice is often based on inferences from indirect evidence, anecdotal experience, and personal bias. Our understanding of the effects of exogenous, as well as endogenous, hormones on normal and neoplastic breast tissue provides some insights but is not an appropriate basis for clinical practice. The effects of exogenous hormone replacement on the overall health of postmenopausal women, including psychosocial issues, cardiovascular risks, and the morbidity of osteoporosis, must be understood before patients can be counseled appropriately. Treatment of patients must be individualized. The rapidly expanding area of nonhormonal therapies for the treatment of postmenopausal health risks and the treatment of symptomatic complaints in postmenopausal women has already led to a reevaluation of the use of exogenous hormones among all women. A prospective randomized trial that examines the effects of hormone replacement on women with a history of breast cancer is currently underway and will provide valuable data to address these issues. The aim of this review is to outline the scientific basis for the association between estrogen and breast cancer and to provide a framework in which individualized recommendations concerning the use of hormone replacement therapy can be made for patients with breast cancer.

Nordic trials of adjuvant therapy in primary breast cancer

The Scandinavian Breast Group (SBG), established in 1989, has members representing research, diagnosis, and treatment of breast cancer. In 1992 the SBG analyzed ongoing adjuvant trials in the Scandinavian countries. Many trials were analyzing similar questions, but a substantial proportion recruited an insufficient number of patients to enable valid conclusions within a reasonable time. As a result the SBG Clinical Trials Group was established to coordinate and organize trials in primary and advanced disease. Present activities include a study in premenopausal patients with node-positive, receptor-positive disease (CMF vs castration), a study in pre- and postmenopausal patients with node-positive, receptor-negative disease (CMF vs CEF), and a study in high-risk patients aged < 60 years (dose-escalating CEF vs three cycles of CEF followed by high-dose chemotherapy and autologous stem cell support). All these studies are planned to close during 1998. Another study has recently been activated. This enrolls patients with climacteric symptoms given previous treatment for in situ or invasive breast cancer, who are randomized to observation vs hormone replacement therapy for 2 years. Other groups are strongly encouraged to participate. Potential future activities are briefly described. Some of these will be undertaken in international collaboration.

Tyrosine kinase inhibitors as antiproliferative agents against an estrogen-dependent breast cancer cell line in vitro

BACKGROUND AND OBJECTIVES

Receptor tyrosine kinase (RTK) activation is critical for growth factor-mediated cell proliferation. Blockade of RTK activation inhibits growth factor-induced cell proliferation. A panel of RTK inhibitors (tyrphostins) have been tested and compared for their antiproliferative effects on the hormone-dependent human breast cancer cell line, MCF-7, in vitro.

METHODS

MCF-7 cells (10(4)/well) were seeded into 96 well plates and maintained in DMEM with 1% bovine serum albumin (BSA), 200-pg/mL estrogen, or 10% fetal bovine serum. After a defined time interval, the cells were exposed to RTK inhibitors and a non-RTK-inhibitory analog of tyrphostins (0 to 400 microM). After 3 days, the number of viable cells in each well was estimated by an MTT assay and the results expressed as percent of controls. Using a representative tyrphostin, A47, the validity of MTT assay as a measure of cell proliferation was tested by a colony formation assay and by immunostaining with Ki-67 antibodies.

RESULTS

MCF-7 cells maintained in DMEM containing 1% BSA without E2 or serum showed a minimal increase in cell number. Supplementation with E2 stimulated cell proliferation in a dose-dependent manner. This E2-mediated growth stimulation was completely inhibited (cytostatic effects) by the epidermal growth factor receptor (EGFR)-selective tyrphostins A47, B48, RG13022, and B50. These same tyrphostins also decreased the cell numbers to below control numbers in cultures maintained in 1% BSA or in serum containing medium (cytostatic/cytotoxic effects). B44 (EGFR-selective tyrphostin), AG1295 (platelet-derived growth factor receptor [PDGFR]-selective tyrphostin), and A1 had no inhibitory effects on cells with or without E2 treatments. However, A1 inhibited cell growth under serum supplementation. Genistein, a phytoestrogen, stimulated the autonomous, E2-induced as well as serum-induced growth of MCF-7 cells. Cell proliferation results derived from the MTT assay were corroborated by both the colony formation assay as well as the Ki-67 assay.

CONCLUSIONS

Of the agents tested, only EGFR-selective tyrphostins blocked E2-stimulated tumor cell proliferation, as opposed to the PDGFR-selective tyrphostin, RTK noninhibitory agent, or the phytoestrogen, genistein, which did not exert such an effect. These findings suggest that epidermal growth factor (EGF) is an important mediator of E2-induced proliferation of MCF-7 cells. Thus, tyrphostins may be selectively used to prevent the growth of hormone-dependent breast cancers, particularly regrowth of residual tumor in postmenopausal breast cancer survivors receiving estrogen replacement therapy.

Hormone replacement therapy in women with previous breast cancer

As breast cancer is known to be a tumour sensitive to the effects of endogenous oestrogens, clinicians are reluctant to prescribe hormone replacement therapy (HRT) to women with a history of previous breast cancer for fear of stimulating disease recurrence, and it is currently contraindicated in this group of women. However, an increasing proportion of breast cancer patients are requesting the use of HRT to relieve the symptoms of oestrogen deficiency, which are also a common side-effect of adjuvant therapy for breast cancer. Observational data on the use of HRT in breast cancer survivors has not demonstrated an increase in disease recurrence, but uncertainty will continue in the absence of data from prospective, randomized trials. This review aims to demonstrate why it is ethical and scientifically important to undertake such studies.