The idea of breast cancer prevention by hormonal means stemmed from the results of treatment trials, many of them carried out by the National Surgical Adjuvant Breast and Bowel Project (NSABP). Over the years, a number of NSABP treatment studies demonstrated that breast cancer recurrence was reduced in women with the disease who were given tamoxifen, a selective estrogen receptor (ER) modulator (SERM). Five subsequent tamoxifen prevention trials with this agent have shown a 48% reduction in ER-positive cancers, but no effect for ER-negative cancers, and an increase in endometrial cancer and thromboembolic events. The drug raloxifene, another SERM, originally examined as an osteoporosis agent, has also shown promise for the prevention of breast cancer, although, as with tamoxifen, the drug carries a risk for thromboembolic events. There is recent evidence in a large treatment trial that the aromastase inhibitor anastrazole, a 'pure anti-estrogen', holds promise as a breast cancer preventive agent. Longer follow-up and the testing of additional agents is required before these drugs can be used widely for prevention. In addition, future research should focus on the identification of at-risk women who can perhaps be targeted for specific prevention agents.
Stephen Hiscox, Nicola J Jordan, Wen Jiang, Maureen Harper, Richard McClelland, Chris Smith, and Robert I Nicholson
Our previous investigations using cell models of tamoxifen resistance have shown that the acquisition of an endocrine-insensitive state is accompanied by an invasive in vitro phenotype. In this study, we wished to determine whether this was specifically related to partial oestrogen receptor agonists or whether similar phenomena arise with the newer ‘pure’ anti-oestrogens, exemplified by fulvestrant. Our data demonstrate that the development of fulvestrant resistance in two breast cancer cell lines, MCF7 and T47D, is accompanied by an augmented migratory and invasive phenotype in vitro and overexpression of the HGF/SF receptor, c-Met. Importantly, upregulated c-Met expression in these cells facilitates their stimulation by HGF/SF-secreting stromal fibroblasts, leading to the activation of Src, Akt and ERK1/2 and a profound enhancement of their aggressive phenotype in vitro. These effects could be specifically attributable to activation of the c-Met receptor since the inclusion of neutralising antibodies to c-Met, or siRNA-mediated knockdown of c-Met expression, suppressed both invasion and migration stimulated by either exogenous HGF/SF, fibroblast-conditioned medium or following co-culture with fibroblast cells. Together, these in vitro data suggest that the development of fulvestrant resistance in vivo may confer a metastatic advantage to the cells by allowing their migratory and invasive behaviour to be augmented by surrounding stromal cells.
R I Nicholson, I R Hutcheson, S E Hiscox, J M Knowlden, M Giles, D Barrow, and J M W Gee
De novo insensitivity and acquired resistance to the selective oestrogen receptor modulator tamoxifen and the pure anti-oestrogen fulvestrant (faslodex) severely limit their effectiveness in breast cancer patients. This is a major clinical problem, since each year upward of 1 million women are dispensed anti-oestrogenic drugs. In order to investigate the phenomenon of anti-oestrogen resistance and to rapidly screen drugs that target the resistance mechanism(s), we have previously established several in vitro breast cancer models that have acquired resistance to anti-hormones. Such cells commonly develop an ability to proliferate after approximately 3 months of exposure to 4-hydroxytamoxifen or fulvestrant, despite an initial endocrine-responsive (i.e. growth-suppressive) phase. The current paper explores the role that growth factor signalling plays in the transition of oestrogen receptor-positive endocrine-responsive breast cancer cells to anti-oestrogen resistance or insensitivity and how we might, in the future, most effectively use anti-growth factor therapies to treat or delay endocrine-resistant states.
Felicity E B May and Bruce R Westley
The stratification of breast cancer patients for endocrine therapies by oestrogen or progesterone receptor expression is effective but imperfect. The present study aims were to validate microarray studies that demonstrate TFF3 regulation by oestrogen and its association with oestrogen receptors in breast cancer, to evaluate TFF3 as a biomarker of endocrine response, and to investigate TFF3 function. Microarray data were validated by quantitative RT-PCR and northern and western transfer analyses. TFF3 was induced by oestrogen, and its induction was inhibited by antioestrogens, tamoxifen, 4-hydroxytamoxifen and fulvestrant in oestrogen-responsive breast cancer cells. The expression of TFF3 mRNA was associated with oestrogen receptor mRNA in breast tumours (Pearson's coefficient=0.762, P=0.000). Monoclonal antibodies raised against the TFF3 protein detected TFF3 by immunohistochemistry in oesophageal submucosal glands, intestinal goblet and neuroendocrine cells, Barrett's metaplasia and intestinal metaplasia. TFF3 protein expression was associated with oestrogen receptor, progesterone receptor and TFF1 expression in malignant breast cells. TFF3 is a specific and sensitive predictive biomarker of response to endocrine therapy, degree of response and duration of response in unstratified metastatic breast cancer patients (P=0.000, P=0.002 and P=0.002 respectively). Multivariate binary logistic regression analysis demonstrated that TFF3 is an independent biomarker of endocrine response and degree of response, and this was confirmed in a validation cohort. TFF3 stimulated migration and invasion of breast cancer cells. In conclusion, TFF3 expression is associated with response to endocrine therapy, and outperforms oestrogen receptor, progesterone receptor and TFF1 as an independent biomarker, possibly because it mediates the malign effects of oestrogen on invasion and metastasis.
S A Khan, D Bhandare, and R T Chatterton Jr
Recent developments in breast epithelial sampling techniques (nipple fluid aspiration, ductal lavage, and random fine needle aspiration) provide new opportunities for the acquisition of hormonal and cellular biomarker data in asymptomatic women, and thereby the possibility of developing a unified vision of how the hormonal environment of the breast may interact with the cellular expression of proteins, and with other evolving candidate markers of breast cancer risk. The purpose of this review is to integrate available information regarding cellular and breast fluid biomarkers of hormone action on the breast, to identify candidate biomarkers for studies of breast cancer risk and prevention. These include the estrogen receptors α andβ, markers of proliferative and apoptotic response, and protein markers of estrogen action in breast cells and nipple fluid. Studies of breast hormone levels in nipple aspiration fluid (NAF) show that estrone sulphate is present in large quantities in the normal breast, while the differences in serum ovarian steroids that are seen in pre- and postmenopausal women are blunted in NAF. The variability of several estradiol precursors in NAF over time is relatively small, a useful attribute of potential biomarkers of breast cancer risk, particularly if they are reversible with intervention in Phase 2 prevention trials. These studies are already providing new insights into the hormonal etiology of breast cancer, and should lead to the identification of robust, reversible biomarkers for use in breast cancer prevention studies.
S Chen, D Zhou, T Okubo, Y C Kao, and C Yang
Aromatase has been shown to be expressed at a higher level in human breast cancer tissue than in normal breast tissue, by means of enzyme activity measurement, immunocytochemistry, and RT-PCR analysis. Cell culture including MCF-7 breast cancer cells, animal experiments using aromatase-transfected breast cancer cells, and transgenic mouse studies have demonstrated that estrogen production in situ plays a more important role than circulating estrogens in breast tumor promotion. In addition, tumor aromatase is believed to be able to stimulate breast cancer growth through both autocrine and paracrine pathways, as demonstrated by a three-dimensional cell culture study. RT-PCR and gene transcriptional studies have revealed that the aromatase promoter is switched from a glucocorticoid-stimulated promoter, I.4, in normal tissue to cAMP-stimulated promoters, I.3 and II, in cancerous tissue. Recently, we identified and characterized a cAMP-responsive element (CREaro) upstream from promoter I.3 by DNA deletion and mutational analyses. Our results from promoter functional analysis also demonstrated an interaction between the CREaro and the silencer element (S1) that was identified previously in our laboratory. In the presence of cAMP, the positive regulatory CREaro can overcome the action of the silencer on the function of promoter I.3. On the basis of results generated from our own and other laboratories, we propose that, in normal breast adipose stromal cells and fibroblasts, aromatase expression is driven by promoter I.4 (glucocorticoid dependent), and that the action of promoters I.3 and II is suppressed by the silencer negative regulatory element. However, in cancer cells and surrounding adipose stromal cells, the cAMP level increases, and aromatase promoters are switched to cAMP-dependent promoters - I.3 and II. Furthermore, we applied the yeast one-hybrid screening method to search for proteins interacting with the silencer element, S1. The major protein identified was ERRalpha-1; however, SF-1, which is present in the ovary, is not detected in breast cancer tissue. Using a reporter plasmid with the aromatase genomic fragment containing promoter I.3 and S1, in breast cancer SK-BR-3 cells, ERRalpha-1 was found to have a positive regulatory function. It is believed that the silencer element in the human aromatase gene may function differently in different tissues, as a result of distinct expression patterns of transcription factors.
N Brünner, M D Johnson, C Holst-Hansen, J F Kiilgaard, E W Thompson, and R Clarke
T M Penning
B R Rao and B J Slotman
Ovarian cancer has a poor prognosis. At the time of diagnosis, in the majority of cases, the disease has progressed to a stage where intra-abdominal dissemination has already taken place. The pathogenesis of ovarian cancer is still unknown. However, epidemiologic studies have demonstrated that endocrine factors may play an important role. Elevated steroid hormone levels have been detected in ovarian cancer patients. The use of endocrine therapy, frequently consisting of progestins and/or tamoxifen, given on an empirical basis and as a last resort, has shown a modest response rate of 10-15%. About 50% of the tumors are positive for estrogen and progesterone receptors (PR). The PR status is a prognostic indicator, independent of the stage of disease, histology and patient's age. The majority of ovarian cancers (>70%) are positive for androgen receptors. Anti-androgens inhibit the growth of ovarian cancer cells in vitro in a majority of cases tested. Clinical trials to evaluate the efficacy of anti-androgen are recommended.
Endocrine-Related Cancer (1996) 3 309-326
Ann M Dorward, Kathryn L Shultz, and Wesley G Beamer
The reproductive hormone environment is an important influence upon spontaneous ovarian granulosa cell (GC) tumor development in genetically susceptible (SWR × SWXJ-9) F1 female mice: androgenic support during puberty stimulates tumorigenesis, while exposure to 17β-estradiol (E2) suppresses tumor initiation. We sought to determine whether gonadotropic stimulation was sufficient to initiate GC tumors in a grafted model system, and to determine the potential for dietary isoflavones (genistein and daidzein) as alternatives to E2 for tumor chemoprevention in vivo. Isolated ovaries from pre-pubertal (SWR × SWXJ-9) F1 females were transferred to the kidney capsule of host mice homozygous for the hypogonadal (hpg/hpg) and severe combined immunodeficiency (scid/scid) mutations. CB17; HPG-Prkdc scid Gnrh1 hpg/Bm host mice received either follicle-stimulating hormone (FSH), or a functional analog for LH human chorionic gonadotropin for 2 consecutive weeks, at which time the ovary grafts were examined for evidence of tumor initiation. LH analog administration, but not FSH, initiated GC tumorigenesis in the graft system, suggesting that the LH surge at puberty initiates GC tumor development in genetically susceptible female mice. To assess the chemopreventive potential of phytoestrogens, GC tumor frequency was compared between (SWR × SWXJ-9) F1 females reared on an isoflavone-free diet versus a diet supplemented with 125 μg/g each of the isoflavones daidzein and genistein. It was observed that (SWR × SWXJ-9) F1 females reared on isoflavone-supplemented diet maintained significantly higher GC tumor frequency (22%) than females reared on isoflavone-free diet (11%), and that non-tumor-bearing siblings reared on the isoflavones had significantly increased ovarian weight, indicative of an overall stimulation of the reproductive hormone axis. The stimulation of GC tumorigenesis by isoflavones, which contrasts with the chemopreventive action of E2 (2.5 mg/kg) administration during pubertal maturation, may result from general stimulation of ovarian growth, and the inability of the genistein and daidzein supplements to suppress LH secretion.