Changes in epidermal growth factor receptor expression and response to ligand associated with acquired tamoxifen resistance or oestrogen independence in the ZR-75-1 human breast cancer cell line

Experimental models of endocrine responsive breast cancer: strengths, limitations, and use

Breast cancers characterized by expression of estrogen receptor-alpha (ER; ESR1) represent approximately 70% of all new cases and comprise the largest molecular subtype of this disease. Despite this high prevalence, the number of adequate experimental models of ER+ breast cancer is relatively limited. Nonetheless, these models have proved very useful in advancing understanding of how cells respond to and resist endocrine therapies, and how the ER acts as a transcription factor to regulate cell fate signaling. We discuss the primary experimental models of ER+ breast cancer including 2D and 3D cultures of established cell lines, cell line- and patient-derived xenografts, and chemically induced rodent models, with a consideration of their respective general strengths and limitations. What can and cannot be learned easily from these models is also discussed, and some observations on how these models may be used more effectively are provided. Overall, despite their limitations, the panel of models currently available has enabled major advances in the field, and these models remain central to the ability to study mechanisms of therapy action and resistance and for hypothesis testing that would otherwise be intractable or unethical in human subjects.

Development and characterisation of acquired radioresistant breast cancer cell lines

BACKGROUND

Radiotherapy plays an important role in the multimodal treatment of breast cancer. The response of a breast tumour to radiation depends not only on its innate radiosensitivity but also on tumour repopulation by cells that have developed radioresistance. Development of effective cancer treatments will require further molecular dissection of the processes that contribute to resistance.

METHODS

Radioresistant cell lines were established by exposing MDA-MB-231, MCF-7 and ZR-751 parental cells to increasing weekly doses of radiation. The development of radioresistance was evaluated through proliferation and colony formation assays. Phenotypic characterisation included migration and invasion assays and immunohistochemistry. Transcriptomic data were also generated for preliminary hypothesis generation involving pathway-focused analyses.

RESULTS

Proliferation and colony formation assays confirmed radioresistance. Radioresistant cells exhibited enhanced migration and invasion, with evidence of epithelial-to-mesenchymal-transition. Significantly, acquisition of radioresistance in MCF-7 and ZR-751 cell lines resulted in a loss of expression of both ERα and PgR and an increase in EGFR expression; based on transcriptomic data they changed subtype classification from their parental luminal A to HER2-overexpressing (MCF-7 RR) and normal-like (ZR-751 RR) subtypes, indicating the extent of phenotypic changes and cellular plasticity involved in this process. Radioresistant cell lines derived from ER+ cells also showed a shift from ER to EGFR signalling pathways with increased MAPK and PI3K activity.

CONCLUSIONS

This is the first study to date that extensively describes the development and characterisation of three novel radioresistant breast cancer cell lines through both genetic and phenotypic analysis. More changes were identified between parental cells and their radioresistant derivatives in the ER+ (MCF-7 and ZR-751) compared with the ER- cell line (MDA-MB-231) model; however, multiple and likely interrelated mechanisms were identified that may contribute to the development of acquired resistance to radiotherapy.

Salinomycin co-treatment enhances tamoxifen cytotoxicity in luminal A breast tumor cells by facilitating lysosomal degradation of receptor tyrosine kinases

Luminal A breast cancer is the most common breast cancer subtype which is usually treated with selective estrogen receptor modulators (SERMS) like tamoxifen. Nevertheless, one third of estrogen receptor positive breast cancer patients initially do not respond to endocrine therapy and about 40% of luminal A breast tumors recur in five years. In this study, we investigated an alternative treatment approach by combining tamoxifen and salinomycin in luminal A breast cancer cell lines. We have found that salinomycin induces an additional cytotoxic effect by inhibiting the ligand independent activation of ERα. Thereby salinomycin increases the intracellular calcium level. This leads to a premature fusion of endosomes with lysosomes and thus to the degradation of Egfr family members. Since this process is essential for luminal A breast cancer cells to circumvent tamoxifen treatment, the combination of both drugs induces cytotoxicity in tamoxifen sensitive as well as resistant luminal A breast cancer cell lines.

Epigenetic modulation: a novel therapeutic target for overcoming hormonal therapy resistance

For more than four decades, modulation of estrogen receptor activity with antiestrogens has been a successful strategy for the treatment of breast cancer. However, therapeutic resistance limits this approach. Patients whose tumors lack estrogen receptors are not candidates for antiestrogens. Furthermore, roughly half that do express estrogen receptors fail to respond. Together, these tumors are considered to be de novo resistant. For those with tumors that do respond, most will eventually acquire resistance. As such, the underlying mechanisms of both de novo and acquired resistance have been the subject of considerable research, so that new therapeutic targets might be discovered and developed. From this work, epigenetic regulation of gene expression has emerged as a major contributor to both forms of resistance. In this article, we present our current understanding of the mechanisms that contribute to antiestrogen resistance, focusing on epigenetic regulation, and examine the approaches being used that target epigenetic machinery to overcome resistance both in the laboratory and in the clinic.

The in vitro and in vivo anti-tumor effect of KO-202125, a sauristolactam derivative, as a novel epidermal growth factor receptor inhibitor in human breast cancer

Epidermal growth factor receptor (EGFR) is one of the most promising targets for cancer therapy. Here, we show the in vitro and in vivo anticancer effects and associated mechanisms of KO-202125, one of the synthesized aristolactam analogs, as a novel EGFR inhibitor, in EGFR-overexpressing cancer cell lines. KO-202125 showed more effective growth inhibition and apoptosis induction than gefitinib, a representative EGFR inhibitor, in various EGFR-overexpressing human cancers including estrogen receptor (ER)-negative MDA-MB-231 human breast cancer cells. Epidermal growth factor receptor phosphorylation at Tyr1068 was reduced and, consequently, the association of EGFR with p85 was decreased by KO-202125 treatment in MDA-MB-231 cell lines. This led to inactivation of the PI3K/Akt pathway, and consequently suppression of activation of the Wnt pathway and enhancement of the nuclear import of p27Kip1. KO-202125 treatment in nude mice injected with MDA-MB-231 cells showed inhibition of tumor growth without toxicity. Collectively, our results showed the possibility of KO-202125 as an effective therapy agent of EGFR-overexpressing cancer cells through reduced EGFR activity and downregulation of the Akt pathway.

E-cadherin mediates the aggregation of breast cancer cells induced by tamoxifen and epidermal growth factor

In the present study, we evaluated the ability of 4-hydroxytamoxifen (OHT) and epidermal growth factor (EGF) to regulate homotypic adhesion in MCF7 breast cancer cells. Our results demonstrate that OHT and EGF activate the E-cadherin promoter, increase E-cadherin mRNA and protein expression and enhance homotypic aggregation of MCF7 cells. Interestingly, an ERalpha and EGFR cross-talk is involved in the E-cadherin expression by OHT and EGF, as demonstrated by knocking down either receptor. On the basis of our findings, the well-established cross-talk between ERalpha and EGFR could be extended to the modulation of E-cadherin expression by OHT and EGF. Thus, the potential ability of tamoxifen to induce cell-cell aggregation may contribute to the biologic response of pharmacologic intervention in patients with breast cancer.

Growth factor signalling in endocrine and anti-growth factor resistant breast cancer

Growth factors provide powerful mitogenic and survival signals to breast cancer cells and it is therefore not surprising that they are able to subvert inhibitory responses to anti-hormonal drugs. In this review we discuss several mechanisms by which this may be achieved and expand our observations to encompass recently emerging anti-growth factor treatments. The information presented is underpinned by inhibitor studies that show the targeting of such mechanisms in advance of anti-hormone or anti-growth factor resistance development is able to substantially delay this event, thus pointing the way forward to intelligent combination therapies relevant to the future management of breast cancer.

Mechanisms of acquired resistance to endocrine therapy in hormone-dependent breast cancer cells

Acquired resistance is a major problem limiting the clinical benefit of endocrine therapy. To investigate the mechanisms involved, two in vitro models were developed from MCF-7 cells. Long-term culture of MCF-7 cells in estrogen deprived medium (LTED) mimics aromatase inhibition in patients. Continued exposure of MCF-7 to tamoxifen represents a model of acquired resistance to antiestrogens (TAM-R). Long-term estrogen deprivation results in sustained activation of the ERK MAP kinase and the PI3 kinase/mTOR pathways. Using a novel Ras inhibitor, farnesylthiosalicylic acid (FTS), to achieve dual inhibition of the pathways, we found that the mTOR pathway plays the primary role in mediation of proliferation of LTED cells. In contrast to the LTED model, there is no sustained activation of ERK MAPK but enhanced responsiveness to rapid stimulation induced by E(2) and TAM in TAM-R cells. An increased amount of ERalpha formed complexes with EGFR and c-Src in TAM-R cells, which apparently resulted from extra-nuclear redistribution of ERalpha. Blockade of c-Src activity drove ERalpha back to the nucleus and reduced ERalpha-EGFR interaction. Prolonged blockade of c-Src activity restored sensitivity of TAM-R cells to tamoxifen. Our results suggest that different mechanisms are involved in acquired endocrine resistance and the necessity for individualized treatment of recurrent diseases.

Long-term treatment with tamoxifen facilitates translocation of estrogen receptor alpha out of the nucleus and enhances its interaction with EGFR in MCF-7 breast cancer cells

The therapeutic benefit of tamoxifen in patients with hormone-dependent breast cancer is limited by acquired resistance to this drug. To investigate the biological alterations responsible for tamoxifen resistance, an in vitro model was established. After 6-month continuous exposure to tamoxifen (10(-7) mol/L), growth of MCF-7 breast cancer cells was no longer inhibited by this antiestrogen. Although there was no significant increase in the basal levels of activated mitogen-activated protein kinase (MAPK), tamoxifen-resistant (TAM-R) cells exhibited enhanced sensitivity to epidermal growth factor (EGF) and estradiol stimulated activation of MAPK. Tamoxifen elicited rapid phosphorylation of MAPK, in contrast to its antagonistic activity in control cells. Blockade of the EGF receptor (EGFR)/MAPK pathway caused more dramatic inhibition of growth of TAM-R cells than the control cells. An increased amount of estrogen receptor alpha (ERalpha) was coimmunoprecipitated with EGFR from TAM-R cells although the total levels of these receptors were not increased. Notably, ERalpha seemed to redistribute to extranuclear sites in TAM-R cells. Increased ERalpha immunoreactivity in the cytoplasm and plasma membrane of TAM-R cells was shown by fluorescent microscopy and by Western analysis of isolated cellular fractions. In TAM-R cells, an increased amount of c-Src was coprecipitated with EGFR or ERalpha. Blockade of c-Src activity resulted in redistribution of ERalpha back to the nucleus and in reduction of its interaction with EGFR. Prolonged blockade of c-Src activity restored sensitivity of TAM-R cells to tamoxifen. Our results suggest that enhanced nongenomic function of ERalpha via cooperation with the EGFR pathway is one of the mechanisms responsible for acquired tamoxifen resistance.

Insulin-like growth factor-I receptor signaling in tamoxifen-resistant breast cancer: a supporting role to the epidermal growth factor receptor

There is considerable evidence that the epidermal growth factor receptor (EGFR) and IGF-I receptor (IGF-IR) cross-talk in breast cancer cells. In the present study, we have examined whether EGFR/IGF-IR cross-talk exists in EGFR-positive tamoxifen-resistant variants of MCF-7 (Tam-R) and T47D (T47D-R) breast cancer cell lines. Although Tam-R cells expressed reduced IGF-IR protein levels compared with their wild-type MCF-7 counterparts, phosphorylated IGF-IR protein levels were equivalent in the two cell lines under basal growth conditions, possibly as a consequence of increased IGF-II expression in Tam-R cells. IGF-II activated both IGF-IR and EGFR in Tam-R cells, whereas only activation of IGF-IR was observed in wild-type cells. In contrast, epidermal growth factor rapidly induced EGFR, but not IGF-IR, phosphorylation in Tam-R cells. IGF-II promoted direct association of c-SRC with IGF-IR, phosphorylated c-SRC, and increased EGFR phosphorylation at tyrosine 845, a c-SRC-dependent phosphorylation site. Pretreatment with either AG1024 (IGF-IR-specific inhibitor) or an IGF-II neutralizing antibody inhibited basal IGF-IR, c-SRC, and EGFR phosphorylation, and AG1024 significantly reduced Tam-R basal cell growth. The c-SRC inhibitor SU6656 also inhibited growth, reduced basal and IGF-II-induced c-SRC and EGFR phosphorylation, and blocked EGFR activation by TGFalpha. Similarly, in T47D-R cells, AG1024 and SU6656 inhibited basal and IGF-II-induced phosphorylation of c-SRC and EGFR, and SU6656 reduced TGFalpha-induced EGFR activity. These results suggest the existence of a unidirectional IGF-IR/EGFR cross-talk mechanism whereby IGF-II, acting through the IGF-IR, regulates basal and ligand-activated EGFR signaling and cell proliferation in a c-SRC-dependent manner in Tam-R cells. This cross-talk between IGF-IR and EGFR is not unique to Tam-R cells because this mechanism is also active in a tamoxifen-resistant T47D-R cell line.

Bidirectional cross talk between ERalpha and EGFR signalling pathways regulates tamoxifen-resistant growth

We have previously demonstrated that oestrogen receptor alpha (ERalpha) modulates epidermal growth factor receptor (EGFR)/mitogen-activated protein kinase (MAPK) signalling efficiency in a tamoxifen-resistant MCF-7 breast cancer cell line (Tam-R). In the present study we have investigated whether this cross-talk between EGFR/MAPK and ERalpha signalling pathways is bidirectional by examining the effects of EGFR/MAPK activity on ER functionality in the same cell line. Elevated expression levels of phosphorylated serine 118 (S118) ERalpha were observed in the Tam-R compared to the parental wild type MCF-7 cell line (WT-MCF-7) under basal growth conditions. Phosphorylation of ERalpha at S118 was regulated by the EGFR/MAPK pathway in Tam-R cells being increased in response to amphiregulin (AR) and inhibited by the selective EGFR tyrosine kinase inhibitor, gefitinib and the MEK1/2 inhibitor, PD184352. Recruitment of the co-activators p68 RNA helicase and SRC1 to ERalpha, oestrogen response element (ERE) activity and Tam-R cell growth were similarly EGFR/MAPK-regulated. Chromatin immunoprecipitation (ChIP) studies revealed that in Tam-R cells the ERalpha assembled on the AR gene promoter and this was associated with elevated basal expression of AR mRNA. Furthermore, AR mRNA expression was under the regulation of the EGFR/MAPK and ERalpha signalling pathways. Neutralising antibodies to AR inhibited EGFR/ERK1/2 activity, reduced S118 ERalpha phosphorylation and reduced AR mRNA expression in TAM-R cells. These findings suggest that ERalpha function in Tam-R cells is maintained as a consequence of EGFR/MAPK-mediated phosphorylation at serine residue 118 resulting in the generation of a self-propogating autocrine growth-regulatory loop through the ERalpha-mediated production of AR.

Serum HER-2/neu conversion to positive at the time of disease progression in patients with breast carcinoma on hormone therapy

BACKGROUND

Prolonged exposure of breast carcinoma cells in vitro to tamoxifen results in tamoxifen resistance. Tamoxifen-resistant cells express increased HER-2/neu mRNA and protein. The objective of this study was to determine whether patients with metastatic or locally advanced breast carcinoma who have negative serum HER-2/neu status at the initiation of first-line hormone therapy with letrozole or tamoxifen convert to positive serum HER-2/neu status at the time of disease progression and to determine whether serum HER-2/neu conversion to positive status is associated with response to therapy and overall survival.

METHODS

Serum samples were obtained at baseline and at the time of disease progression from 240 patients who initially had negative serum HER-2/neu status (< 15 ng/mL). A manual microtiter, enzyme-linked immunosorbent assay that was specific for the extracellular domain of the HER-2/neu (c-erbB-2) oncoprotein product was used to quantitate serum levels.

RESULTS

Among 240 patients, 61 patients (26%) converted from serum HER-2/neu negative to positive (> 15 ng/mL) at the time of disease progression. Thirty-two of 129 patients (25%) who were treated with tamoxifen and 29 of 111 patients (26%) who were treated with letrozole became converted to positive serum HER-2/neu status at the time of disease progression. The response rate and the time to disease progression on first-line hormone therapy were not affected by serum HER-2/neu conversion. The survival of patients who converted to positive serum HER-2/neu status was significantly shorter compared with the survival of patients who remained negative for serum HER-2/neu. A multivariate analysis revealed that conversion to positive serum HER-2/neu status was an independent prognostic variable for survival.

CONCLUSIONS

Conversion to positive serum HER-2/neu status occurred in approximately 25% of patients who received first-line hormone therapy. Conversion to serum HER-2/neu-positive status occurred with equal frequency in antiestrogen and aromatase-inhibitor therapy. The current results showed that serum conversion to HER-2/neu-positive status was an independent risk factor for decreased survival in patients with breast carcinoma.

Tamoxifen resistance in breast cancer cells is accompanied by an enhanced motile and invasive phenotype: inhibition by gefitinib ('Iressa', ZD1839)

Despite an initial response to antihormonal therapies, the development of resistance will occur in a significant number of breast cancer patients. The mechanisms that underlie acquired resistance are not yet clear. Using a previously established in vitro cell model of tamoxifen resistance in MCF7 cells, shown to display autocrine epidermal growth factor receptor (EGFR) signalling, we assessed how resistance might modulate their metastatic phenotype in vitro, as metastatic disease is the single most important factor affecting the mortality of cancer patients. Furthermore, we investigated the effect of the EGFR tyrosine kinase inhibitor (EGFR-TKI), gefitinib ('Iressa', ZD1839; AstraZeneca), on this behaviour. The acquisition of tamoxifen resistance in MCF7 cells was accompanied by a dramatic and significant increase in their invasive and motile nature. The affinity of these cells for matrix components was also enhanced. Inhibition of EGFR signalling with gefitinib reduced both basal and TGF-alpha-stimulated invasion and motility and reduced cell-matrix adhesion. In conclusion, we demonstrate here that resistance to tamoxifen in breast cancer cells is accompanied by a significant increase in their basal motile and invasive activity, properties associated with increased metastatic potential. Inhibition of EGFR signalling by gefitinib significantly inhibited cell motility and invasion thus suggesting a role for the EGF receptor in the aggressive phenotype of tamoxifen-resistant breast cancer cells.

Increased Constitutive Activity of PKB/Akt in Tamoxifen Resistant Breast Cancer MCF-7 Cells

The tamoxifen-resistant (TAM-R) MCF-7 breast cancer cell line has been used as a model to identify the signalling pathways that enable resistant cancer cells to grow independently of steroid hormones. In TAM-R cells, peptide growth factor signalling pathways appear to be important in modified cell behaviour, growth and survival. The PI3 kinase signalling components Akt1 and Akt2 are expressed at similar levels by both parental wild-type MCF-7 and TAM-R cells, but Akt1 phosphorylation is significantly increased in TAM-R cells grown under basal conditions. High levels of basal Akt, GSK3 alpha / beta and p70S6 kinase phosphorylation are all inhibited by the PI3 kinase inhibitor, LY 294002. The ligands for the EGFR/erbB1 receptor, EGF (epidermal growth factor) and TGF alpha (transforming growth factor- alpha ) demonstrate an increased ability to activate Akt in TAM-R compared with parental MCF-7 cells and it is proposed that the preferred autocrine or paracrine activation of Akt occurs via the erbB heterodimer EGFR/erbB2 in TAM-R cells. Akt phosphorylation is reduced by gefitinib ("Iressa"/ZD1839). The results suggest that the PI3 kinase pathway plays a role in proliferation of TAM-R cells and is important in the increased EGF induced membrane ruffling detected in the resistant cells. Increased Akt1 activation may contribute to the aggressive phenotype of tamoxifen resistant ER (oestrogen receptor) positive breast cancers.

Additive antitumour effect of the epidermal growth factor receptor tyrosine kinase inhibitor gefitinib (Iressa, ZD1839) and the antioestrogen fulvestrant (Faslodex, ICI 182,780) in breast cancer cells

A high expression level of epidermal growth factor receptor (EGFR)/HER1 has been suggested to lead to a shorter survival time and resistance to endocrine therapy in patients with breast cancer. To test the hypothesis that inhibition of the EGFR signalling pathway affects the antitumour effect of endocrine therapy, an EGFR tyrosine kinase inhibitor (EGFR-TKI), gefitinib, and an oestrogen receptor (ER) antagonist, fulvestrant, were administered to human breast cancer cells. A total of five human breast cancer cell lines were used. The effects of single or combined treatments with gefitinib and/or fulvestrant on cell growth, cell cycle progression and apoptosis were analysed. Changes in the expression levels of cyclin-dependent kinase inhibitors, p21 and p27, an antiapoptotic factor, Bcl-2, and a proapoptotic factor, Bax, were also investigated. All cell lines tested were sensitive to gefitinib (50% growth inhibitory concentration, 10–28.5 μM). Breast cancer cell lines with a high expression level of HER1 or HER2 were more sensitive to gefitinib than the others. Gefitinib induced a significant G1–S blockade in ER-positive KPL-3C cells. Gefitinib induced significant apoptosis in HER1-overexpressing MDA-MB-231 cells. Gefitinib additively increased the antitumour effect of fulvestrant in all three ER-positive cell lines in a medium supplemented with 17β-oestradiol. The combined treatment promoted cell cycle retardation in KPL-3C cells, which is associated with an upregulation of p21 by fulvestrant and gefitinib, respectively. Apoptosis was associated with downregulation of Bcl-2 by gefitinib in MDA-MB-231 cells. These results suggest an additive interaction between the EGFR-TKI gefitinib and the antioestrogen fulvestrant in ER-positive breast cancer cells.

Nonendocrine Pathways and Endocrine Resistance

An increasing body of evidence demonstrates that growth factor networks are highly interactive with estrogen receptor signaling in the control of breast cancer growth. As such, tumor responses to antiestrogens are likely to be a composite of the estrogen receptor and growth factor-inhibitory activity of these agents, with alterations/aberrations in growth factor signaling providing a mechanism for the development of antiestrogen resistance. In this light, the current article focuses on illustrating the relationship between growth factor signaling and antiestrogen failure in our in-house tumor models of breast cancer and describing how we are now beginning to successfully target growth factor activity to improve the effects of antiestrogen drugs and to block aggressive disease progression.

The antiepidermal growth factor receptor agent gefitinib (ZD1839/Iressa) improves antihormone response and prevents development of resistance in breast cancer in vitro

Although many estrogen receptor-positive breast cancers initially respond to antihormones, responses are commonly incomplete with resistance ultimately emerging. Delineation of signaling mechanisms underlying these phenomena would allow development of therapies to improve antihormone response and compromise resistance. This in vitro investigation in MCF-7 breast cancer cells examines whether epidermal growth factor receptor (EGFR) signaling limits antiproliferative and proapoptotic activity of antihormones and ultimately supports development of resistance. It addresses whether the anti-EGFR agent gefitinib (ZD1839/Iressa; TKI: 1 mum) combined with the antihormones 4-hydroxytamoxifen (TAM: 0.1 mum) or fulvestrant (Faslodex; 0.1 mum) enhances growth inhibition and prevents resistance. TAM significantly suppressed MCF-7 growth over wk 2-5, reducing proliferation detected by immunocytochemistry and fluorescence-activated cell sorter cell cycle analysis. A modest apoptotic increase was observed by fluorescence-activated cell sorter and fluorescence microscopy, with incomplete bcl-2 suppression. EGFR induction occurred during TAM response, as measured by immunocytochemistry and Western blotting, with EGFR-positive, highly proliferative resistant growth subsequently emerging. Although TKI alone was ineffective on growth, TAM plus TKI cotreatment exhibited superior antigrowth activity vs. TAM, with no viable cells by wk 12. Cotreatment was more effective in inhibiting proliferation, promoting apoptosis, and eliminating bcl-2. Cotreatment blocked EGFR induction, markedly depleted ERK1/2 MAPK and protein kinase B phosphorylation, and prevented emergence of EGFR-positive resistance. Faslodex plus TKI cotreatment was also a superior antitumor strategy. Thus, increased EGFR evolves during treatment with antihormones, limiting their efficacy and promoting resistance. Gefitinib addition to antihormonal therapy could prove more effective in treating estrogen receptor-positive breast cancer and may combat development of resistance.

Oestrogen Receptor-Mediated Modulation of the EGFR/MAPK Pathway in Tamoxifen-Resistant MCF-7 Cells

Oestrogen receptor (ER) levels are usually maintained on acquisition of tamoxifen resistance in the clinic, however, tumour re-growth is associated with increased expression of epidermal growth factor receptor (EGFR) and activation of the mitogen activated protein kinase (MAPK) pathway. In the present study we have used the ER down-regulator fulvestrant ('Faslodex') to investigate the influence of the ER on growth of a tamoxifen-resistant (TAM-R) human breast cancer cell line. Expression levels of ER mRNA and protein were equivalent in parental wild-type MCF-7 (WT) and TAM-R cells. Fulvestrant eliminated ER protein expression and inhibited proliferation in both cell lines. The growth inhibitory effects of fulvestrant were associated with a decrease in basal EGFR, c-erbB2 and ERK1/2 activity in TAM-R but not WT cells. ER functionality as determined by oestrogen response element (ERE)-luciferase reporter activity and expression of PgR, pS2 and transforming growth factor alpha (TGFalpha) was significantly reduced in TAM-R compared to WT cells and was further decreased by fulvestrant treatment in both cell lines. Epidermal growth factor (EGF) and TGFalpha significantly increased EGFR/MAPK pathway activity in both cell lines. Ligand-induced EGFR/MAPK activation promoted TAM-R cell growth in both the absence and presence of fulvestrant, whereas no proliferative activity was observed under the same conditions in WT cells. These results suggest that the ER modulates EGFR/MAPK signalling efficiency in TAM-R cells possibly through the regulation of TGFalpha availability. This effect may be overcome by the action of exogenous EGFR ligands, which strengthen EGFR/MAPK signalling activity to generate endocrine-insensitive cell growth.

Elevated levels of epidermal growth factor receptor/c-erbB2 heterodimers mediate an autocrine growth regulatory pathway in tamoxifen-resistant MCF-7 cells

The development of acquired resistance to antihormonal agents in breast cancer is a major therapeutic problem. We have developed a tamoxifen-resistant (TAM-R) MCF-7 breast cancer cell line to investigate the mechanisms behind this condition. Both epidermal growth factor receptor (EGFR) and c-erbB2 mRNA and protein expression were increased in TAM-R compared with wild-type MCF-7 cells, whereas comparable levels of c-erbB3 mRNA and protein were expressed in both cell lines. Under basal conditions, phosphorylated EGFR/c-erbB2, EGFR/c-erbB3 but not c-erbB2/c-erbB3 receptor heterodimers were detected in TAM-R cells in association with increased levels of phosphorylated extracellular-signal regulated kinase 1/2 (ERK1/2). Both cell lines were capable of generating a range of EGFR-specific ligands and increased expression of transforming growth factor alpha was observed in TAM-R cells. Treatment of TAM-R cells with ZD1839 (Iressa) or trastuzumab (Herceptin) blocked c-erbB receptor heterodimer formation and phosphorylation, reduced ERK1/2 activity, and strongly inhibited cell growth. The MAPK kinase inhibitor PD098059 specifically reduced phosphorylated ERK1/2 levels and inhibited TAM-R growth. All three agents abolished ERK1/2 activity in wild-type cells but caused only small reductions in cell proliferation. These results demonstrate that TAM-R MCF-7 cell growth is mediated by the autocrine release and action of an EGFR-specific ligand inducing preferential EGFR/c-erbB2 dimerization and downstream activation of the ERK pathway.

Absence of c-KIT and members of the epidermal growth factor receptor family in refractory germ cell cancer

BACKGROUND

Germ cell tumors (GCTs) in adolescent and young males are very sensitive to cisplatin-based chemotherapy. However, 10-20% of the patients cannot be cured by currently available therapeutic options. Once a tumor does not respond to cisplatin, current therapeutic modalities offer only a chance for short palliation. Recently, new treatment options that interfere with various receptor tyrosine kinases, including c-KIT and members of the epidermal growth factor receptor (EGFR) family, have been used successfully in chemotherapy-resistant tumors overexpressing c-KIT, ERB-B2, or EGFR.

METHODS

We studied the presence of c-KIT and the four members of the EGFR family by immunohistochemistry, as well as by ERB-B2 gene amplification using fluorescent in situ hybridization, in a series of 22 patients with cisplatin-resistant GCTs in search of new treatment targets. The results in these refractory tumors were compared with those of 12 patients with chemosensitive GCTs diagnosed in an advanced metastatic stage.

RESULTS

The data obtained in both groups did not differ in any of the investigated biologic markers. c-KIT was detected in the one case of pure seminoma studied and in the seminomatous components of combined tumors. The presence of EGFR was restricted to trophoblastic giant cells and the syncytiotrophoblastic elements of four nonseminomas including one pure choriocarcinoma and to a secondary non-germ cell malignancy, which had developed most likely from a mature teratoma. ERB-B2 was moderately positive in the secondary non-germ cell malignancy, in one mature teratoma component of a mixed nonseminoma, and together with EGFR in the syncytiotrophoblastic cells of a pure choriocarcinoma. Of all samples investigated, this latter case was the only one showing an amplification of the ERB-B2 gene in the syncytiotrophoblasts. ERB-B3 and ERB-B4 were detected rarely.

CONCLUSION

The majority of refractory GCTs do not qualify for treatment with new biologic agents targeting the receptor tyrosine kinases EGFR, ERB-B2, or c-KIT. The lack of differences between the tumors of refractory and the responsive patients indicates that overexpression of any of these receptor tyrosine kinases does not contribute to a resistant phenotype in GCTs.

Molecular perspectives on selective estrogen receptor modulators (SERMs): progress in understanding their tissue-specific agonist and antagonist actions

Synthetic estrogen receptor ligands such as tamoxifen and raloxifene produce biologic responses which can be either estrogenic or anti-estrogenic, depending upon the tissue in which their action is examined. To reflect the fact that they are not 'pure' antagonists, such ligands have been more accurately termed selective estrogen receptor modulators (SERMs). Recent progress in our understanding of the molecular biology of estrogen receptor (ER) action has provided a great deal of evidence which promises to increase our understanding of the mechanism through which SERMs elicit their tissue-specific effects. The identification of numerous coactivators and corepressors which modulate receptor function and the realization of two subtypes of ER attest to the potential complexity through which SERMs produce diverse tissue-specific responses. Evidence from co-crystal structures of ER ligand-binding domains complexed with SERMs provides additional information as to how this class of ligands can elicit diverse biologic responses. SERMs also influence the stability of the ER protein, and recent information on the determinants of receptor stability and the role of proteasome-mediated protein degradation in ER-driven transcription also promises to give a fuller understanding of SERM biology. These aspects of the molecular biology of estrogen receptor action may help clarify the mechanism(s) of SERM biologic action and will be addressed in further detail in this review.

Expression of oncogenic epidermal growth factor receptor family kinases induces paclitaxel resistance and alters beta-tubulin isotype expression

Oncogenic transformation confers resistance to chemotherapy through a variety of mechanisms, including suppression of apoptosis, increased drug metabolism, and modification of target proteins. Oncogenic epidermal growth factor receptor family members, including EGFRvIII and HER2, are expressed in a broad spectrum of human malignancies. Cell lines transfected with EGFRvIII and HER2 are more resistant to paclitaxel-mediated cytotoxicity, and tubulin polymerization induced by paclitaxel is suppressed compared with cells expressing wild type epidermal growth factor receptor. Because differential expression of beta-tubulin isotypes has been proposed to modulate paclitaxel resistance, we analyzed beta-tubulin isotypes expressed in cell lines transfected with different oncogenes. EGFRvIII- and HER2-expressing cells demonstrated equivalent total beta-tubulin protein compared with cells transfected with wild type receptor or untransfected controls. EGFRvIII-expressing cells demonstrated increases in class IVa (2.5-fold) and IVb (3.1-fold) mRNA, and HER2-expressing cells showed increases in class IVa (2. 95-fold) mRNA. Expression of oncogenic Ha-Ras did not change class IV RNA levels significantly. Inhibition of EGFRvIII kinase activity using a mutant allele with an inactivating mutation in the kinase domain decreased expression of class IVa by 50% and partially reversed resistance to paclitaxel. Expression of oncogenic epidermal growth factor receptor family members is associated with modulation of both beta-tubulin isotype expression and paclitaxel resistance in cells transformed by expression of the receptor. This effect on tubulin expression may modulate drug resistance in human malignancies that express these oncogenes.

The anti-proliferative effects of tyrosine kinase inhibitors towards tamoxifen-sensitive and tamoxifen-resistant human breast cancer cell lines in relation to the expression of epidermal growth factor receptors (EGF-R) and the inhibition of EGF-R tyrosine kinase

We have investigated the anti-proliferative effect of the tyrosine kinase inhibitors genistein, lavendustin A and 2,5-dihydromethylcinnimate (2,5-MeC) (a stable erbstatin analogue) against the epidermoid A431 cell line, the ZR-75-1 human breast cancer cell line and tamoxifen-resistant (ZR-75-9a1) and oestrogen-independent (ZR-PR-LT) variants. Increased EGF-R expression by ZR-75-9a1 was associated with decreased sensitivity to genistein and 2,5-MeC whilst decreased EGF-R expression (ZR-PR-LT) cells was associated with increased sensitivity to lavendustin A and 2,5-MeC. Anti-proliferative IC50 concentrations of 2,5-MeC, but not genistein or lavendustin A, inhibited EGFR-R associated tyrosine kinase activity of ZR-75-1 cells and variants by 20-50%.

The anti-proliferative effect of suramin towards tamoxifen-sensitive and resistant human breast cancer cell lines in relation to expression of receptors for epidermal growth factor and insulin-like growth factor-I: growth stimulation in the presence of tamoxifen

BACKGROUND

A significant proportion of breast cancer patients receiving tamoxifen therapy relapse during treatment following acquisition of tamoxifen-resistant or oestrogen-independent phenotypes. The mechanism behind this rapid progression to oestrogen autonomy is at present unclear and further treatment modalities are limited. Suramin represents a novel potential second line therapy. The mechanism of the antineoplastic activity of suramin is not completely understood, although the drug binds to many growth factors including epidermal growth factor and insulin-like growth factors and can also dissociate growth factors from their receptors. In this study we have related suramin sensitivity to the expression of receptors for epidermal growth factor and insulin-like growth factor-I in a number of breast cancer cell lines including lines resistant to tamoxifen.

MATERIALS AND METHODS

The anti-proliferative effects of suramin were investigated in two oestrogen dependent breast cancer lines (ZR-75-1 and MCF-7), oestrogen independent (ZR-PR-LT) and tamoxifen resistant (ZR-75-9a1) variants of ZR-75-1 and a tamoxifen resistant (LY2) variant of MCF-7. Full dose response curves were constructed and IC50 values determined for each cell line. Sensitivity to suramin was correlated with the level of expression of receptors for epidermal growth factor (EGFR) and insulin-like growth factor-I (IGFR). On observing stimulation of cell proliferation by suramin in the tamoxifen resistant cell lines in the presence of tamoxifen we also investigated the possible role of suramin sequestration of transforming growth factor-beta in mediating this effect.

RESULTS

All cell lines exhibited a dose- and time-dependent response to suramin treatment. Tamoxifen resistant ZR-75-9a1 cells (day 6 IC50 85 micrograms ml-1) were more resistant to suramin than oestrogen independent ZR-PR-LT cells (day 6 IC50 45 micrograms ml-1), and the parent ZR-75-1 line (day 6 IC50 56 micrograms ml-1). Increased sensitivity to suramin was associated with increased expression of IGFR and decreased expression of EGFR. Tamoxifen resistant LY2 cells were significantly more sensitive to suramin (day 6 IC50 70 micrograms ml-1) than MCF-7 cells (day 6 IC50 350 micrograms ml-1). Both IGFR and EGFR expression by LY2 cells was lower than in the parent line. The antioestrogen-resistant ZR-75-9a1 and LY2 lines grown in the presence of 8 microM tamoxifen were growth stimulated by concentrations of the drug below 100 micrograms/ml. As growth stimulation observed in the presence of tamoxifen may have been due to suramin sequestration of tamoxifen induced TGF-beta 1 secretion we also investigated the response of the cells to this peptide in the presence and absence of suramin. All cell lines were growth inhibited by TGF-beta 1 except ZR-75-9a1 which was unresponsive. Responses to TGF-beta 1 were modified in the presence of 100 micrograms suramin ml-1 although TGF-beta 1 was unable to mimic the ability of tamoxifen to stimulate proliferation in the presence of suramin.

CONCLUSIONS

These results suggest that for ZR-75-1 cells and variants, increased sensitivity to suramin is associated with an increase in expression of IGFR and a decrease in EGFR numbers. However, tamoxifen resistant LY2 cells, in which both IGFR and EGFR expression is reduced were considerably more sensitive than parental MCF-7 cells suggesting that there is no clear relationship between EGFR and IGFR expression and suramin sensitivity. The unexpected stimulation of cell proliferation of the tamoxifen resistant variants by suramin in the presence of tamoxifen could not be explained by suramin sequestration of transforming growth factor-beta and the mechanism of this interaction remains unclear.

Changes in insulin-like growth factor-I receptor expression and binding protein secretion associated with tamoxifen resistance and estrogen independence in human breast cancer cells in vitro

Conditioned medium from a series of human breast cancer cell lines representing the phenotypes of estrogen dependence ZR-75-1, MCF-7), tamoxifen resistance (Z(+)-75-9a1, LY2) and estrogen independence (ZR-PR-Lt) contained four detectable insulin-like growth factor binding proteins (IGFBPs) of MW 24, 34, 44 and 70 kDa. in the tamoxifen resistant lines secretion of the 24 kDA IGFBP was depressed in comparison to the parent lines whilst secretion of the 44 kDa IGFBP was unaffected. Secretion of this species by ZR-PR-LT cells was reduced. Following incubation in medium containing 1% serum both tamoxifen resistant cell lines secreted higher levels of the 44 kDa IGFBP than the respective parent lines. These changes in IGFBP secretion associated with the development of tamoxifen resistance and estrogen independence were accompanied by changes in the expression of receptors for IGF-1.

Reduced levels of cathepsin D associated with tamoxifen resistance and estrogen independence in the ZR-75-1 human breast cancer cell line

The expression and secretion of cathepsin D by ZR-75-1 human breast cancer cells, and tamoxifen-resistant (ZR-75-9a1) and estrogen-independent (ZR-PR-LT) variants was examined by electrophoresis of labeled proteins and Western blotting. Secreted proteins of 160 kDa, 52 kDa and 34 kDa were identified, and in ZR-75-1 cells, they were shown to be estrogen-inducible. Treatment of ZR-75-9a1 cells with 17 beta-estradiol (E2) and the progestin ORG 2058 increased secretion of the 52 kDa protein; ZR-PR-LT cells were unaffected. Western blotting showed that each cell line expressed high levels of the 52 kDa and 34 kDa forms of cathepsin D but that relatively little was being secreted. Each cell line secreted 52 kDa procathepsin D, but 34 kDa mature-cathepsin D was not detected as a secreted protein. ZR-75-1 cells expressed and secreted the highest levels of cathepsin D while ZR-75-9a1 cells expressed and secreted the least.

Expression of receptors for epidermal growth factor and insulin-like growth factor I by ZR-75-1 human breast cancer cell variants is inversely related: the effect of steroid hormones on insulin-like growth factor I receptor expression

We have investigated the expression of insulin-like growth factor I receptors (IGFR) by the ZR-75-1 human breast cancer cell line and tamoxifen-resistant (ZR-75-9a1) and oestrogen-independent (ZR-PR-LT) variants. ZR-75-1 cells expressed 6633+/-953 receptors per cell,(K(d) 0.24+/-0.06 nM). IGFR expression was reduced in ZR-75-9a1 cells (1180+/-614 receptors per cell, K(d) 0.13+/-0.05) and increased in the ZR-PR-LT cell line (18 430+/-3210 receptors per cell, K(d) 0.24+/-17). A comparison of these data with previously published findings for epidermal growth factor receptor (EGFR) expression by these cell lines revealed that IGFR and EGFR expression are inversely related in the variant lines whereas ZR-75-1 cells express similar numbers of both receptors. Since the changes in IGFR expression observed are associated with changes in steroid hormone receptor status, we also investigated the effects of oestradiol, the synthetic progestin ORG 2058 and dexamethasone on IGFR expression. Oestradiol increased IGFR expression only in the ZR-75-1 cell line. Low concentrations of ORG 2058 increased IGFR levels in the two cell lines positive for progesterone receptor (ZR-75-1 and ZR-PR-LT). High concentrations of ORG 2058 increased IGFR expression in all cell lines, as did dexamethasone. These data suggest that EGFR and IGFR expression may be linked in breast cancer, and that EGFR/IGFR ratios in breast cancer may be a more sensitive prognostic indicator than EGFR expression alone. Regardless of basal IGFR expression by the cell studied, ORG 2058 increased IGFR expression, possibly via both the progesterone and glucocorticoid receptors.

Expression of estrogen, progesterone and epidermal growth factor receptors in primary and metastatic breast cancer

The prognostic value of epidermal growth factor receptor (EGFR) expression and its biological role in estrogen receptor-positive (ER+) and ER-negative (ER-) primary breast cancer is controversial. In this study, distributions of ER, progesterone receptor and EGFR have been established using immunohistochemistry in both primary breast tumors and their matched axillary lymph node metastases of 26 patients or their matched distant metastases of 2 patients. In addition, 5 patients with bilateral breast cancer were studied. ER+ tumor cells were detected in 22 (69%) and EGFR+ tumor cells were detected in 11 (34%) primary breast carcinomas. Expression of ER and EGFR was inverse regarding the individual tumor cells in both primary tumors and metastases. Relationship of EGFR expression with poorly differentiated and large breast tumors was observed. Furthermore, primary tumors with a predominant lobular component were ER+ and, with one exception, EGFR-. Invasive ductal carcinomas were more frequently EGFR+. No apparent differences in receptor expression were observed between primary tumors and lymph node metastases or chronously or metachronously occurring bilateral breast cancers. Only one ER+ primary tumor showed a switch to EGFR expression in the involved lymph node. Our study shows that a shift in receptor phenotype between primary tumors and lymph node metastases is a rare event and, thus, additional analyses of involved lymph nodes will not likely serve as a better predictor for response to anti-estrogen therapy. We conclude that expression of EGFR is not a prerequisite for development of metastases.

Outgrowth of BT-474 human breast cancer cells in immune-deficient mice: a new in vivo model for hormone-dependent breast cancer

The effect of co-inoculation of basement membrane matrix, Matrigel and two human breast cancer cell lines, BT-474 and SK-BR-3, was tested in immune-deficient mice. Both cell lines strongly overexpress c-ErbB-2 protein, whereas only BT-474 is reported to be oestrogen receptor positive. Co-inoculation of Matrigel and BT-474 cells but not of Matrigel and SK-BR-3 cells resulted in tumour formation in bg-nu-xid mice. Oestrogen supplementation greatly enhanced tumorigenicity, but did not seem to be an absolute requirement. In vivo, BT-474 cells grow as a poorly differentiated adenocarcinoma with a doubling time of 9.4 +/- 1.1 days after inoculation into the neck region. A high proliferative activity appears to be compensated by a relatively high rate of cell loss, as BT-474 tumours contain many cells with the typical morphology of apoptotic cell death. Wild-type p53, known to participate in the induction of apoptosis, is absent from the tumours, whereas Bcl-2, known to inhibit apoptosis, is expressed at intermediate levels. BT-474 tumours tend to metastasise to the regional lymph nodes and are capable of forming micrometastatic lesions in the lung. Flow cytometrical analysis of DNA ploidy demonstrated no change in tumours compared with the cell line. Immunohistochemical and flow cytometrical detection of a number of hormone and growth factor receptors, transcription factors, cell adhesion molecules and proteins involved in proliferation and cell death demonstrated no major changes in ploidy and phenotype of tumours compared with the cell line. High expression of the cell-surface molecules c-ErbB-2 and episialin make it a potentially useful model for research in immune therapy.

The prognostic value of epidermal growth factor receptor (EGF-R) in primary breast cancer: results of a 10 year follow-up study

In a study on 214 patients with primary breast cancer (median follow-up 8.5 yr, maximum follow-up 15 yr), EGF-R was negatively correlated to estrogen receptor and progesterone receptor, whereas no association was found with age, lymph node status, and tumor size. Initially, after a follow-up of 5 yr, there was a tendency to a significant association between EGF-R levels and tumor recurrence rate (p = 0.08). Patients with tumors containing intermediate levels of EGF-R experienced a longer relapse-free survival (RFS) than did patients with tumors possessing lower or higher levels of EGF-R. This effect was most pronounced in the subgroup of patients with positive axillary lymph nodes. However, after 10 yr follow-up, this association appears to be lost (p = 0.28) as shown in this update. A similar phenomenon was observed for the ER. While at 5 yr follow-up ER status had significant prognostic value (p = 0.01), at 10 yr follow-up this significance also appears to be lost (p = 0.40). However, tumor size, lymph node status, grade, and PgR status maintained significant prognostic value by univariate analysis. Based on 40 separate studies comprising 5232 patients, the mean percentage of EGF-R positivity reported in breast cancer is 45% (range 14-91%). Nine out of 15 different studies showed in some way a significant negative association between EGF-R and RFS by univariate analysis, and 2 others showed a tendency to such a relationship. Of 7 studies applying multivariate analysis, two demonstrated an independent prognostic value of EGF-R for RFS and two others a tendency to a significant correlation, whereas three did not. It may be concluded that EGF-R status has more or less prognostic value in patients with primary breast cancer, but the prognostic power decreases with longer follow-up. Of great clinical significance is the association of EGF-R with hormone resistance. Therefore EGF-R status can be used for selection of type of treatment. Finally, EGF-R might be useful as a target for new treatment modalities.

Epidermal growth factor receptor expression in breast cancer: association with response to endocrine therapy

106 previously untreated breast cancer patients have been immunohistochemically analysed for EGF-R, ER, Ki67, and c-erbB-2 product. All patients received assessable endocrine therapy following disease progression. Significant associations were observed between EGF-R and ER (inverse) and Ki67 (direct). No association was observed between EGF-R and the c-erbB-2 product. EGF-R expression was significantly associated with the loss of endocrine sensitivity in breast cancer. This was observed in both ER positive and negative disease. In ER positive breast cancers, EGF-R expression had no significant influence on the quality of tumour remissions. Further sub-classification of the ER/EGF-R data by Ki67 immunostaining showed that in ER+/EGF-R-disease, increasing proportions of Ki67 positive cells were associated with a decline in the numbers of women experiencing good quality tumour remissions. A similar trend was also observed in ER+/EGF-R+ tumours. The presence of c-erbB-2 protein product did not influence endocrine sensitivity in any of the ER/EGF-R sub-groups.

Preclinical models for the evaluation of targeted therapies of metastatic disease

It has been estimated that approx 60-70% of cancer patients harbor overt or subclinical metastases at diagnosis, and it is the eradication of such systemic disease that largely determines survival. Preclinical tumor model systems employed to evaluate potential new treatment strategies should aim to represent the process and patterns of metastasis of their clinical counterparts as closely as possible. Severe combined immune-deficient (SCID) and nu/nu mice have been extensively used as hosts for the growth of human tumor cell lines and in some cases fresh tumor material. However, in most instances the resulting neoplasms fail to metastasize, and the aberrant immune systems of such animals has limited their use mainly to passive therapies of localized disease. Recently, the development of specially selected tumor variants and the use of appropriate orthotopic sites for implantation has provided several models in which dissemination can be demonstrated. Where the gene coding for a potential target antigen has been cloned, and where its overexpression or mutation is associated with malignancy (e.g., c-erbB-2, H-ras), transgenic mice may yield tumors that will develop in these immunocompetent hosts. In some cases such tumors exhibit metastasis. A third approach is to transfect human genes of interest into appropriate rodent tumors expressing the desired metastatic phenotype. These various approaches are compared with particular reference to mammary carcinoma biology.

EGF receptor in neoplasia and metastasis

EGFR is a member of the tyrosine kinase family of cell surface receptors with a wide range of expression throughout development and in a variety of different cell types. The receptor can transmit signals to cells: i) upon interaction with ligands such as EGF, TGF alpha, amphiregulin or heparin binding EGF, ii) upon truncation or mutation of extracellular and/or intracellular domains, iii) upon amplification of a basal receptor activity (in the absence of ligand) through cooperation with other cellular signaling pathways or nuclear events (e.g. expression of v-erbA). The activated EGFR can exert pleiotropic functions on cells, depending on their tissue origin and state of differentiation. Under certain conditions it can also contribute to neoplasia and development of metastases. Such conditions can exist upon aberrant receptor/ligand expression and activation (e.g. in the wrong cell; at the wrong time; in the wrong amounts). Aberrant signalling can also occur through constitutive EGFR activation. Oncogenic potential of EGFR has been demonstrated in a wide range of experimental animals. EGFR is also implicated in human cancer, where it may contribute both to the initiation (glioblastoma) and progression (epithelial tumors) of the disease. EGFR may influence key steps in the processes of tumor invasion and dissemination. Involvement of EGFR in tumor spread may indicate a potential use of this receptor as a target for antimetastatic therapy.

Cell biological factors associated with the response of breast cancer to systemic treatment

A large number of cell biological parameters are currently available to predict the prognosis of patients with breast cancer, but it is still difficulty accurately to predict the response to treatment. A valuable prognostic factor can be a poor predictive factor for response, and vice versa. High tumor levels of ER, PgR, AR and pS2 predict a relatively good response to endocrine therapy, while EGF-R positively, HER2/neu positivity, aneuploidy, high proliferation indices and possibly high uPA levels indicate a high chance of poor response to endocrine therapy in metastatic breast cancer. With respect to chemotherapy, a high proliferation rate and HER2/neu amplification predict a good response to therapy in metastatic disease, while MDR gene expression and possibly c-myc amplification are related to a worse response. In conclusion, the newer cell biological parameters can be used to select high and low-risk patients, type of systemic treatment, and as targets for new treatment modalities.