Up-regulation of estrogen receptor by tamoxifen in human breast cancer

Role of Estrogen Receptor-Positive/Negative Ratios in Regulating Breast Cancer

The alpha estrogen receptor (ERα) contributes to breast cancer progression and recent guidelines define ER positivity as ≥1% stained cells, and a few tumor tissues show no ERα expression at all or are at 100%. Although ER and aromatase inhibitors are widely used to treat hormone receptor-positive (HR+) breast cancer, their effect on tumor activity at different ERα levels remains unclear. Therefore, we investigated the role of ERα+/ERα− ratios in determining the ERα level. We used ERα stably transfected and wild-type MDA-MB-231 cells (MDA-MB-231^Trans−ER and MDA-MB-231^WT, respectively) as represented ER+ and ER− cells, respectively, and MCF-7 cells were the positive control. MDA-MB-231^Trans−ER and MDA-MB-231^WT cells were mixed and cocultured at a ratio of 0%, 20%, 40%, 70%, and 100%. Migration and invasion functions at different cell ratios were evaluated in vitro using the Transwell and scratch test. In a xenograft mouse model, the polarization of the tumor-associated (M2) macrophage and the expression of breast cancer gene 1 (BRCA1), human epidermal growth factor receptor 2 (HER2), vascular endothelial growth factor (VEGF), and tumor necrosis factor (TNF)-α were measured. The results showed that the cell invasion and migration were significantly higher at 40% and 70% than they were at other ratios. Additionally, in vivo, the 70% ERα+/ERα-ratio was a critical indicator of cell activity and cytokine expression. The highest M2 level and expression of VEGR, TNF-α, BRCA1, and HER2 were shown at a ratio of 70%. Moreover, the effects of ERα were not linear in breast cancer, indicating that the ERα status requires continuous monitoring during long-term endocrine treatment. These results indicate that during HR+ breast cancer treatment, the ERα+/ERα− ratio may be a useful predictor and should be evaluated further.

Can estrogen receptor overexpression in normal tissues due to previous estrogen deprivation explain the fulvestrant efficacy in breast cancer therapy?

Fulvestrant is a down-regulator of estrogen receptors (ERs) with still evolving optimal dosage for ER-positive breast cancer patients. The CONFIRM phase III trial in women with advanced breast cancer proved fulvestrant 500-mg to be associated with a longer time till progression (TTP) than the 250-mg schedule. Detailed results suggest that the fulvestrant in both schedules depended on the previous endocrine therapy. All complete responses and the only significant TTP difference between the two schedules was found among women previously treated with tamoxifen (TAM) and not in women after aromatase inhibitors (AIs). Noting that TAM competes with estrogen binding to ERs is important, so the optimal TAM dosage produces drug concentrations comparable to concentrations of available ER ligands. All AIs diminish production of the main ER ligand, so the optimal AI dosage depends on the overall pool of aromatase molecules in the body. Both treatments are not directly related to the pool of available ERs in the body. Here proposed interpretation is that estrogen deprivation due to years of endocrine breast cancer therapy increases ER expression in breast cancer cells and in other healthy estrogen target tissues. The breast cancer exposure to fulvestrant depends on the presence of all ERs in the body. Only when this overall pool is sufficiently saturated with fulvestrant, we can expect to achieve some breast cancer response due to down-regulation of ER in cancer tissue. The CONFIRM data suggest that among patients switching from TAM to fulvestrant, only the 500-mg schedule could down-regulate the moderately enlarged total body ER pool and thus induce breast cancer regression. In patients switching from previous AI treatments, both 250 and 500-mg schedules were unable to prolong the TTP, suggesting that in both doses, fulvestrant showed no efficacy since the overall ER pool was more enlarged after AIs. Fulvestrant might be more effective before TAM and AIs, in the first line endocrine therapy of metastatic breast cancer, since an unaltered ER pool in normal tissues is expected in this setting.

Comparison of the effects of the PI3K/mTOR inhibitors NVP-BEZ235 and GSK2126458 on tamoxifen-resistant breast cancer cells

BACKGROUND

Treatment with anti-estrogens or aromatase inhibitors is commonly used for patients with estrogen receptor-positive (ER+) breast cancers; however resistant disease develops almost inevitably, requiring a choice of secondary therapy. One possibility is to use inhibitors of the PI3K/mTOR pathway and several candidate drugs are in development. We examined the in vitro effects of two inhibitors of the PI3K/mTOR pathway on resistant MCF-7 cells.

METHODS

We cultured MCF-7 cells for prolonged periods either in the presence of the anti-estrogen tamoxifen (3 sub-lines) or in estrogen free medium (2 sub-lines) to mimic the effects of clinical treatment. We then analyzed the effects of two dual PI3K/mTOR phosphoinositide-3-kinase inhibitors, NVP-BEZ235 and GSK2126458, on the growth and signaling pathways of these MCF-7 sub-lines. The functional status of the PI3K, mTOR and ERK pathways was analyzed by measuring phosphorylation of AKT, p70S6K, rpS6 and ERK.

RESULTS

The derived sub-lines showed increased resistance to tamoxifen but none exhibited concomitantly increased sensitivity to the PI3K inhibitors. NVP-BEZ235 and GSK2126458 acted mainly by induction of cell cycle arrest, particularly in G1-phase, rather than by induction of apoptosis. The lines varied considerably in their utilization of the AKT, p70S6K and ERK pathways. NVP-BEZ235 and GSK2126458 inhibited AKT signaling but NVP-BEZ235 showed greater effects than GSK2126458 on p70S6K and rpS6 signaling with effects resembling those of rapamycin.

CONCLUSION

Increased resistance to tamoxifen in these MCF-7 sub-lines is not associated with hypersensitivity to PI3K inhibitors. While both drugs inhibited AKT signaling, NVP-BEZ235 resembled rapamycin in inhibiting the mTOR pathway.

Imaging pharmacodynamics in oncology: the potential significance of "flares"

The clinical use of (18)F-fluorodeoxyglucose (FDG) positron emission tomography in monitoring anticancer treatment is expanding. At the same time a number of radiotracers aiming to image different aspects of tumour biology such as proliferation and apoptosis are being developed. However, the factors determining changes of radiotracer uptake parameters in response to treatment are not well understood. In many cases, cellularity may be the primary determinant of changes of FDG uptake and may confound the interpretation of metabolic changes. Early imaging assessments have in some cases showed transient increases of uptake parameters, commonly termed "flares", which are likely to be unaffected by cellularity and directly reflect pharmacodynamics at a cellular level. In this review a number of settings where molecular imaging "flares" have been described are discussed. Such changes may often be clinically informative and warrant careful study as potential predictive biomarkers.

Relationship of cellular immunity, cytokines and CRP with clinical course in breast cancer patients with endocrine-dependent distant metastases treated with immunotherapy

We have reported important benefits and survival with an immunotherapy schedule in patients with endocrine-dependent breast cancer and distant metastases. Here clinical outcome is updated and its correlation with new immunological data is shown. In 32 evaluated breast cancer patients with endocrine-dependent distant metastases treated with a new immunotherapy schedule (cyclic administration of beta-interferon and interleukin-2), cellular immunity, cytokines and CRP were related to the clinical course. Estimated and true 5-10 year overall survival rates from first line antiestrogen and distant metastases were higher than previously reported in a similar population. Interleukin-2 administration was followed by a significant increase in total lymphocytes, CD4+, CD8+, CD16+56+ (NK) cells, IL-6, IL-12, and CRP (from P<0.04 to P<0.000) but no change in IL-10 and TGFbeta1 during clinical benefit. During progressive disease no change was observed in the former parameters, concomitant with a significant increase in IL-10 (P=0.020) and a significant decrease in TGFbeta1 (P=0.023). These findings confirm that cellular immunity is significantly stimulated by IL-2 only during clinical benefit. Furthermore, these results demonstrate that different changes of proinflammatory cytokines, CRP and inhibiting factors are consistent with associated clinical benefit or with disease progression, respectively.

Beta-interferon and interleukin-2 prolong more than three times the survival of 26 consecutive endocrine dependent breast cancer patients with distant metastases: an exploratory trial

Distant metastases from breast cancer are incurable. In endocrine-responsive patients antiestrogens are commonly administered as first and second line therapy. Regrettably, tumor growth becomes resistant to this relatively innocuous therapy. Beta-interferon was unsuccessfully added to tamoxifen to induce estrogen receptor enhancement. In mice, interleukin-2 added to tamoxifen increased their mutual anti-tumor activities. Nevertheless, no effective clinical application has been developed. We started an exploratory clinical trial based on the association of these immunostimulating cytokines with antiestrogens for first line salvage therapy of hormone dependent breast cancer with distant metastases. Twenty-six consecutive breast cancer patients with distant metastases, 23 of which had metastases at multiple sites, were studied for responsiveness to treatment with first line salvage antiestrogen therapy, combined with beta-interferon and interleukin-2 immuno-therapy. Clinical response and survival were compared with that of 30 consecutive historical control patients treated with antiestrogen therapy alone. Controls showed, as expected, a median duration of response, a median survival time after treatment, and after diagnosis of distant metastases, of 16, 31 and 34 months, respectively. After a mean follow-up of 62+/-36 months (range 17-155), the interval times in the non-control patients were 61 (P<0.001), 101 (P<0.000001) and 106 (P<0.000001) months. Two long-term survivors appeared to be cured after 155 and 94 months from the time of diagnosis with multiple bone metastases. Nineteen of the patients treated with beta-interferon and interleukin-2 have survived. Hormone immuno-therapy was given in an outpatient setting and was very well tolerated. These data suggest that immuno-therapy plays an important role in endocrine-dependent metastatic breast cancer.

Positron emission tomography in the staging and management of breast cancer

Background

Breast cancer is the commonest cause of cancer death in women in the Western world, and imaging is essential in its diagnosis and staging. Metabolic imaging is a novel approach to improving the detection of cancers, as malignant transformation of cells is often associated with increased metabolic activity. This review assesses the possible role of positron emission tomography (PET) as a single non-invasive imaging modality to replace or complement current imaging and surgical practices in the diagnosis and staging of breast cancer.

Methods and results

A Medline search was performed and articles were cross-referenced with other relevant material. Evaluation of primary breast cancer with PET has shown a sensitivity of between 64 and 100 per cent and a specificity of 33–100 per cent; diagnostic accuracy appears to be related to tumour size. Difficulties arise in altered fluorodeoxyglucose uptake in lobular carcinoma, carcinoma in situ and benign inflammatory breast disease. In axillary staging, sensitivities of between 25 and 100 per cent have been reported, but with a false-negative of up to 20 per cent. In the assessment of distant metastasis and asymptomatic patients with raised levels of tumour markers, PET was superior to conventional imaging modalities.

Conclusion

PET is not a single diagnostic and staging tool that can replace current surgical, histological and radiological staging. Its main role in breast cancer lies in the investigation of metastatic disease and the evaluation of pathological response to various chemotherapeutic regimens.

Metabolic flare: indicator of hormone responsiveness in advanced breast cancer

PURPOSE

The purpose of this study was to investigate whether positron emission tomography (PET) with the glucose analog [(18)F]fluorodeoxyglucose (FDG) and the estrogen analog 16 alpha-[(18)F]fluoroestradiol-17 beta (FES), performed before and after treatment with tamoxifen, could be used to detect hormone-induced changes in tumor metabolism (metabolic flare) and changes in available levels of estrogen receptor (ER). In addition, we investigated whether these PET findings would predict hormonally responsive breast cancer.

PATIENTS AND METHODS

Forty women with biopsy-proved advanced ER-positive (ER(+)) breast cancer underwent PET with FDG and FES before and 7 to 10 days after initiation of tamoxifen therapy; 70 lesions were evaluated. Tumor FDG and FES uptake were assessed semiquantitatively by the standardized uptake value (SUV) method. The PET results were correlated with response to hormonal therapy.

RESULTS

In the responders, the tumor FDG uptake increased after tamoxifen by 28.4% +/- 23.3% (mean +/- SD); only five of these patients had evidence of a clinical flare reaction. In nonresponders, there was no significant change in tumor FDG uptake from baseline (mean change, 10.1% +/- 16.2%; P =.0002 v responders). Lesions of responders had higher baseline FES uptake (SUV, 4.3 +/- 2.4) than those of nonresponders (SUV, 1.8 +/- 1.3; P =.0007). All patients had evidence of blockade of the tumor ERs 7 to 10 days after initiation of tamoxifen therapy; however, the degree of ER blockade was greater in the responders (mean percentage decrease, 54.8% +/- 14.2%) than in the nonresponders (mean percentage decrease, 19.4% +/- 17.3%; P =.0003).

CONCLUSION

The functional status of tumor ERs can be characterized in vivo by PET with FDG and FES. The results of PET are predictive of responsiveness to tamoxifen therapy in patients with advanced ER(+) breast cancer.

Does tamoxifen change oestrogen and progesterone receptor expression in the endometrium and breast?

We studied the expression of oestrogen and progesterone receptors (ER, PR) in postmenopausal women receiving tamoxifen for breast cancer. In addition the literature addressing the question of ER and PR expression in breast tissue during treatment with tamoxifen was reviewed. We demonstrated consistent expression of ER and PR in endometria from patients receiving tamoxifen, with a trend towards a higher proportion of receptor positive specimens during tamoxifen. In breast cancer tissue, the ER content seemed to be reduced following tamoxifen treatment. After short time exposure to tamoxifen, the PR appeared to be increased, longer treatment caused the PR to go down to pretreatment levels or below.

Development and characterization of a tamoxifen-resistant breast carcinoma xenograft

A human tamoxifen-resistant mammary carcinoma, MaCa 3366/TAM, originating from a sensitive parental xenograft 3366 was successfully established by treatment of tumour-bearing nude mice with 1-50 mg kg(-1) tamoxifen for 3 years during routine passaging. Both tumours did not differ significantly in OR- and PR-positivity, however, when compared with the sensitive tumour line, the mean OR content of the TAM-resistant subline is slightly lower. An OR-upregulation following withdrawal of oestradiol treatment was observed in the parental tumours but not in the resistant xenografts. Following long-term treatment with tamoxifen, the histological pattern of the breast carcinoma changed. The more differentiated structures being apparent after treatment with 17beta-oestradiol in the original 3366 tumour were not induced in the resistant line. Tamoxifen failed to induce a tumour growth inhibition in comparison to the tamoxifen-sensitive line. The pure anti-oestrogen, ICI 182 780, revealed cross-resistance. Sequence analysis of the hormone-binding domain of the OR of both lines showed no differences, suggesting that either mutations in other regions of the OR are involved in the TAM-resistance phenotype or that mechanisms outside of this protein induced this phenotype. Oestrogen and anti-oestrogen regulate pS2 and cathepsin D expression in 3366 tumours as in the human breast cancer cell line MCF-7. The resistant 3366/TAM tumours have lost this regulation. The established breast cancer xenografts 3366 and 3366/TAM offer the possibility of investigating mechanisms of anti-oestrogen resistance in an in vivo situation. They can be used to test novel approaches to prevent, or to overcome, this resistance in a clinically related manner.

Antiestrogens--tamoxifen, SERMs and beyond

Estrogens play a central role in reproductive physiology. The cellular effects of estrogens are mediated by binding to nuclear receptors (ER) which activate transcription of genes involved in cellular growth control. At least two such receptors, designated ERalpha and ERbeta, mediate these effects in conjunction with a number of coactivators. These receptors can directly interact with other members of the steroid receptor superfamily. A complex cross-talk exists between the estrogen-signaling pathways and the downstream signaling events initiated by growth factors, such as epidermal growth factor and insulin-like growth factors. Estrogens are also a causative factor in the pathogenesis of a variety of neoplastic and non-neoplastic diseases, including breast cancer, endometrial cancer, endometriosis, and uterine fibroids, among others. Antiestrogens, such as tamoxifen, are widely used for the treatment of breast cancer. Tamoxifen produces objective tumor shrinkage in advanced breast cancer, reduces the risk of relapse in women treated for invasive breast cancer, and prevents breast cancer in high-risk women. Although, initially developed as an antiestrogen, tamoxifen can also prevent postmenopausal osteoporosis as well as reduce cholesterol, due to its estrogen-agonist effects. Its estrogen-agonist activity, however, can lead to significant side-effects such as endometrial cancer and thromboembolic phenomena. This has led to the concept of "ideal" selective estrogen receptor modulators (SERMs), drugs that would have the desired, tissue selective, estrogen-agonist or -antagonist effects. Raloxifene is a SERM which has the desirable mixed agonist/antagonist effects of tamoxifen but does not cause uterine stimulation. "Pure" antiestrogens may provide very potent estrogen-antagonist drugs, but are likely to be devoid of beneficial effects on bone and lipids. Future drug development efforts should focus on developing superior SERMs that have a greater efficacy against ER-positive tumors and do not cause hot flashes or thromboembolism, and explore combination strategies to simultaneously target hormone-dependent as well as hormone-independent breast cancer.

Suppression of parathyroid hormone-related protein messenger RNA expression by medroxyprogesterone acetate in breast cancer tissues

The level of parathyroid hormone-related protein (PTHrP) expressed in breast cancer tissue is closely related to the incidence of bone metastasis. We examined the PTHrP mRNA expression in breast cancer tissues by coamplification polymerase chain reaction (PCR) in mole ratio to internal standard beta-actin mRNA. The PTHrP expression was higher in premenopausal patients than in postmenopausal patients (P < 0.05). More pronounced difference by menopause found in estrogen receptor (ER) positive groups (P < 0.001) indicated that the PTHrP expression in breast cancer tissue is hormonally regulated and might be altered by endocrine agents. To clarify the changes of PTHrP expression by endocrine therapy of breast cancer, we measured PTHrP expression in the breast cancer tissue incubated for 24 h with 1 x 10(-8) M of estradiol (E2), 1 x 10(-6) M of tamoxifen (TAM) and 1 x 10(-5) M of medroxyprogesterone acetate (MPA). The PTHrP expression was decreased significantly by MPA (P < 0.005), while E2 and TAM did not change the PTHrP expression. Progesterone receptor (PgR) mRNA expression was also examined to confirm that the breast cancer tissue responds to E2 and TAM. The results were well compatible with the better therapeutic effect of MPA reported for the treatment of breast cancer with bone metastases. As a potential candidate for the receptor that mediates the suppressive effect of MPA, androgen receptor (AR) is suggested most probable. Present results also demonstrated that the clinical response of individual tumors is closely associated with the early in vitro changes of gene expression detected in the cancer specimen.

Insulin-like growth factors control the regulation of oestrogen and progesterone receptor expression by oestrogens

Ligands for the type I insulin-like growth factor (IGF) receptor interact with oestrogens to control the proliferation of oestrogen responsive breast cancer cells. The aim of this study was to determine the involvement of ligands for the type I IGF receptor in the regulation of oestrogen receptor (OR) expression by oestrogens and antioestrogens in these cells. Oestrogen decreased OR mRNA levels in MCF-7 cells whereas it increased them in T47D, EFM-19 and ZR-75 cells. In MCF-7 cells, IGF-I and insulin lowered further OR expression in the presence of oestrogen. In the presence of IGF-I or insulin, the induction of progesterone receptor mRNA by oestradiol was considerably attenuated in MCF-7 cells, showing that the enhanced down-regulation of OR mRNA levels influenced the expression of oestrogen-regulated genes. The oestrogen agonist activity of the antioestrogens tamoxifen and ICI 182 780 for the down-regulation of OR expression in MCF-7 cells was modulated by type I IGF receptor ligands. Overall these experiments show that OR expression is differentially regulated by oestrogen in individual oestrogen-responsive breast cancer cell lines. Ligands for the type I IGF receptor can modulate regulation of OR expression by oestrogens and antioestrogens principally in cells in which oestrogens down-regulate OR expression.

Study of the action of tamoxifen on the mammary gland epithelium of premenopausal patients by lysosome quantification

Tamoxifen is an antiestrogen drug widely utilized for the adjuvant hormonal treatment of breast carcinoma. Its use in the primary prophylaxis of this disease is currently being proposed. Although the drug has few side effects, its precise action on breast tissue that has not undergone neoplastic transformation has not been fully elucidated. This prospective, randomized study assessed the estrogen activity of tamoxifen on the mammary gland epithelium of premenopausal patients using a quantitative analysis of mammary epithelium lysosome identified by the cytochemical technique of GOMORI for acid phosphatase and by light microscopy. Tamoxifen significantly increased the number of lysosomes only during the secretory phase of the menstrual cycle. We concluded that the early effect of the drug on normal mammary tissue is synergistic with the effect of estrogen during the premenopausal period.

Induction of TGF-beta by an antiprogestin in the human breast cancer cell line T-47D

BACKGROUND

Antiprogestins appear to be a new approach for the endocrine therapy of breast cancer. Most breast cancer cells are growth inhibited by TGF-beta. Any change of tumorcellular TGF-beta secretion could have some impact on tumorcellular growth. We addressed our question to whether the antiprogestin onapristone can induce TGF-beta secretion in breast cancer cells in vitro and whether a possible induction correlates with the antiproliferative effect and the receptor status of the cells.

MATERIALS AND METHODS

We examined the ER and PR positive breast cancer cell lines MCF7 and T-47D and an ER and PR negative variant T-47D/x. Hormone receptor levels were determined by EIA, total (LTGF-beta + active TGF-beta) and active TGF-beta by a radioreceptor assay. All cell biological and antiproliferative effects were measured during basal, not estrogen-stimulated growth.

RESULTS

To our knowledge, we are the first to describe, that the TGF-beta secretion of tumor cells can be increased by an antiprogestin (total: 4.8-fold, active 2.9-fold). A stimulation was found only in the markedly PR positive T-47D cells, in which onapristone proved to have strong antiproliferative potency. In the MCF7 and T-47D/x cells onapristone showed no induction of TGF-beta. Moreover, those cells were not growth inhibited. Whereas onapristone did not influence the ER-content, it dramatically downregulated the PR-content of the T-47D and MCF7 cells (93% and 65%, respectively).

CONCLUSIONS

These observations make it likely, that the antiproliferative potency of the antiprogestin onapristone is at least partly due to the ability of onapristone, to stimulate the strong growth inhibitor TGF-beta. In contrast to the antiprogestin RU 486, onapristone showed no estrogenic activity (stimulation of growth and PR), which could be a decisive advantage in the therapy of breast cancer, taking into account, that many breast carcinomas grow estrogen dependent.

Cell cycle expression of steroid receptors determined by image analysis on human breast cancer cell line: a hypothesis on the effects of antiestrogens

Tamoxifen is the widespread anti-hormonal compound used for the treatment of human breast cancer. It is admitted that its effects are mediated via estrogen receptors (ER) but the molecular basis of its activity has yet to be clearly defined. In this work, we have developed a new image cytometry procedure in order to clarify the interactions between steroid receptors and tamoxifen at the cell cycle kinetic level. On untreated cells, an increase of ER level and a decrease of progesterone receptor (PR) level during the G0/G1 phase were demonstrated. Then, the ER and PR levels fell during the S-phase until the beginning of G2/M phase, where an increase was observed, especially for PR. These results suggest that ER is synthesized preferentially during the G0/G1 transition and PR during the S/G2 transition. After short-term tamoxifen treatment an augmentation of ER level was observed which was not dose-dependent, suggesting an increase in receptor translation rather than an augmentation of ER synthesis. PR level declined in the majority of the population leading to a selection of a subset of proliferating PR negative cells after treatment. These data demonstrate that the synthesis of steroid receptors is linked with the progression of cells through the cell cycle and indicate that tamoxifen blocks MCF-7 cells in G1 via its interactions with ER. Our multifluorescence imaging procedure appears to provide a rapid and quantitative approach which is useful for investigating alterations in steroid receptors after endocrine treatment.

A phase II chemoprevention trial design to identify surrogate endpoint biomarkers in breast cancer

Surrogate biomarkers for risk assessment and efficacy of potential chemopreventive agents are needed to improve the efficiency and reduce the cost of conducting chemoprevention trials. In addition to criteria of sensitivity, specificity, quantifiability, and reproducibility applicable to most potential biomarkers, there are additional specific constraints in developing biomarkers for specific organ sites. In the case of breast tissue, these difficulties include lack of a consensus on the nature of premalignant lesions and the histologic criteria used to define them; even when such a consensus can be evolved, there are limitations in visualizing such lesions without invasive biopsies. Also, knowledge of specific genetic and biochemical changes in premalignant lesions is limited. In addition, the physiology of breast tissue is cyclic, no proven, relevant markers can be studied in a randomly obtained needle aspirate. The earliest determinate lesion that can be recognized in breast tissue is ductal carcinoma in situ (DCIS). At the University of Texas M.D. Anderson Cancer Center, we have initiated a study to develop biomarkers for tamoxifen and 4-hydroxyphenylretinamide by administering one or both of these drugs to women with DCIS or small invasive lesions in the interval between the initial diagnostic core biopsy and definitive surgery. The treatment is to be administered for 2-4 weeks. Proposed biomarkers to be studied include: (a) markers associated with neoplastic phenotypes, e.g., excessive proliferation, alternations of nuclear morphology and angiogenesis; (b) proteins likely to be required for response to the putative chemopreventive agents, e.g., estrogen receptor, nuclear retinoid receptors; (c) markers indicative of intact downstream response pathways, e.g., progesterone receptors; (d) oncogenes and tumor suppressor genes regulated by the proposed chemopreventive agents, e.g., neu, TGF-beta; and (e) potential novel markers of genetic instability that could be studied in randomly obtained needle aspirates, i.e., random chromosomal gains and losses in high risk mammary epithelium. The experience gained in designing and conducting this trial is expected to facilitate development of future chemoprevention trials of breast, as well as other organ site cancers.

Fourteenth Gaddum Memorial Lecture. A current view of tamoxifen for the treatment and prevention of breast cancer

Tamoxifen has been found to be a safe and effective treatment for all stages of breast cancer. Long term tamoxifen therapy is associated with some rare, but potentially serious, side effects so patients should be carefully monitored. However, long term tamoxifen therapy is also associated with a number of physiological benefits over and above its tumouristatic action. These benefits include a decrease in the development of contralateral breast cancer, the maintenance of bone density in postmenopausal women and a decrease in cardiovascular disease. The successful application of tamoxifen to treat breast cancer has increased enthusiasm to test its worth to prevent breast cancer. Although there are individual requests by patients for tamoxifen to prevent breast cancer, individual treatment is inappropriate. Tamoxifen can only be adequately evaluated as a preventive in randomized, double-blind clinical trials. These trials are in place and physicians should encourage women to participate and establish a new therapeutic option as rapidly as possible.

Strategies for the application of biomarkers for risk assessment and efficacy in breast cancer chemoprevention trials

Current chemoprevention trial designs based on epidemiological risk assessment and occurrence of cancer as an endpoint are inefficient and expensive. Novel biomarkers are needed to facilitate the development of chemopreventive interventions. The following four categories of biomarkers may be useful in prevention trials: histologic and morphometric markers; phenotypic markers of dysregulated proliferation, differentiation, and cell loss; specific oncogenes and growth regulators which are qualitatively or quantitatively altered in breast cancers; and markers of genetic and epigenetic instability. Some of these markers will be generally useful regardless of the chemopreventive approach used, whereas others may be uniquely useful in trials of specific chemopreventive agents [e.g., upregulation of progesterone receptor (PR) expression in response to tamoxifen]. The development of these markers requires three phases of study: "Phase I": assessing the prevalence of the putative marker in malignant and premalignant tissue from individuals who have developed breast cancer; "Phase II": assessing in vivo modulation of the biomarker by the proposed chemopreventive agent; and "Phase III": applying the proposed biomarker in larger-scale trials of chemopreventive agent in high-risk populations, either before or after the development of a primary breast malignancy. The use of these biomarkers may also allow identification of novel targets for chemoprevention.