Lapatinib combined with letrozole versus letrozole and placebo as first-line therapy for postmenopausal hormone receptor-positive metastatic breast cancer

Lapatinib, a Dual-Targeted Small Molecule Inhibitor of EGFR and HER2, in HER2-Amplified Breast Cancer: From Bench to Bedside

The HER-2/neu gene product is a 185 kDa Type I receptor tyrosine kinase which consists of an extracellular domain, transmembrane domain, kinase domain, and cytoplasmic tail. The initial discovery that amplification and subsequent overexpression of the HER-2/neu oncogene plays a pivotal role in the pathogenesis of 20%–25% of breast cancers has since led to significant clinical advances in the management of this subtype of breast cancer. The first approved HER2-targeted therapy, trastuzumab, is a humanized monoclonal antibody against the extracellular domain of HER2 and has demonstrated survival benefits in both the metastatic and adjuvant settings. Lapatinib, a small molecule tyrosine kinase inhibitor of both the epidermal growth factor receptor (EGFR) and HER2 is now also approved for advanced HER2-amplified breast cancer and is currently being evaluated in the adjuvant setting. Importantly, lapatinib has been shown to have activity in women with HER2-amplified breast cancer that is refractory to trastuzumab. In addition, it has been shown to extend survival in the front-line setting in combination with letrozole for estrogen receptor (ER) positive, HER2-positive breast cancer. Here we will review the biologic rationale and pre-clinical data that drove its initial clinical development as well as current clinical data and ongoing studies.

Gefitinib or placebo in combination with tamoxifen in patients with hormone receptor-positive metastatic breast cancer: a randomized phase II study

PURPOSE

Increased growth factor signaling may contribute to tamoxifen resistance. This randomized phase II trial assessed tamoxifen plus placebo or the epidermal growth factor receptor inhibitor gefitinib in estrogen receptor (ER)-positive metastatic breast cancer.

EXPERIMENTAL DESIGN

Patients with newly metastatic disease or recurred after adjuvant tamoxifen (stratum 1), or recurred during/after adjuvant aromatase inhibitor (AI) or after failed first-line AI (stratum 2), were eligible. Primary variables were progression-free survival (PFS; stratum 1) and clinical benefit rate (CBR; stratum 2). A 5% or more improvement in response variables with gefitinib was considered to warrant further investigation. Outcome was correlated with biomarkers measured on the primary tumor.

RESULTS

In stratum 1 (n = 206), the PFS HR (gefitinib:placebo) was 0.84 (95% CI, 0.59-1.18; median PFS 10.9 versus 8.8 months). In the stratum 1 endocrine therapy-naïve subset (n = 158) the HR was 0.78 (95% CI, 0.52-1.15), and the prior endocrine-treated subgroup (n = 48) 1.47 (95% CI, 0.63-3.45). In stratum 1, CBRs were 50.5% with gefitinib and 45.5% with placebo. In stratum 2 (n = 84), CBRs were 29.2% with gefitinib and 31.4% with placebo. Biomarker analysis suggested that in stratum 1 there was greater benefit with gefitinib in patients who were ER-negative or had lower levels of ER protein.

CONCLUSIONS

In stratum 1, the improved PFS with gefitinib plus tamoxifen met the protocol criteria to warrant further investigation of this strategy. In stratum 2, there was a numerical disadvantage for gefitinib; additional investigation after AI therapy is not warranted. Studies of predictive biomarkers are needed to subset appropriate patients.

Therapeutic targeting of epidermal growth factor receptor in human cancer: successes and limitations

Epidermal growth factor receptor (EGFR) is one of the most commonly altered genes in human cancer by way of over-expression, amplification, and mutation. Targeted inhibition of EGFR activity suppresses signal transduction pathways which control tumor cell growth, proliferation, and resistance to apoptosis. Small molecule tyrosine kinase inhibitors and monoclonal antibodies are among the most common EGFR-targeting agents and have been used clinically for treating various malignancies. This review discusses the successes and challenges of targeting EGFR in human cancer. The genetic alterations of EGFR tend to occur more often in some solid tumors than others, as do the mechanisms of resistance to targeted inhibition. The clinical and basic science experiences with these agents thus far have important implications for the future of therapeutic targeting of EGFR.

Mechanisms of endocrine resistance in breast cancer

The estrogen receptor (ER) pathway plays a pivotal role in breast cancer development and progression. Endocrine therapy to block the ER pathway is highly effective, but its usefulness is limited by common intrinsic and acquired resistance. Multiple mechanisms responsible for endocrine resistance have been proposed and include deregulation of various components of the ER pathway itself, alterations in cell cycle and cell survival signaling molecules, and the activation of escape pathways that can provide tumors with alternative proliferative and survival stimuli. Among these, increased expression or signaling of growth factor receptor pathways, especially the EGFR/HER2 pathway, has been associated with both experimental and clinical endocrine therapy resistance. New treatment combinations targeting both ER and growth factor receptor signaling to block the crosstalk between these pathways and eliminate escape routes have been proven highly effective in preclinical models. Results of recent clinical studies, while partly supporting this approach, also highlight the need to better identify a priori the patients whose tumors are most likely to benefit from these specific cotargeting strategies.

Long-term cultures of stem/progenitor cells from lobular and ductal breast carcinomas under non-adherent conditions

A small subpopulation of stem/progenitor cells can give rise to the diversity of differentiated cells that comprise the bulk of the tumor. Are proliferating cells, within the bulk of tumor, few cells with uncommon features? The cell biological approach provides a limitless model for studying the hierarchical organization of progenitor subpopulation and identifying potential therapeutic targets. Aim of the study was to expand patients' breast cancer cells for evaluating functional cell properties, and to characterize the protein expression profile of selected cells to be compared with that of primary tumors. Breast cancer cells from estrogen receptor (ERα) positive, HER2 negative lobular (LoBS cells) and ductal (DuBS cells) histotype were cultured under non-adherent conditions to form mammospheres. Sorting of the cells by their surface expression of CD24 and CD44 gave rise to subpopulations which were propagated, enriched and characterized for the expression of epithelial and stromal markers. We found that non-adherent culture conditions generate mammospheres of slowly proliferating cells; single cells, dissociated from mammospheres, grow in soft agar; long-term cultured LoBS and DuBS cells, CD44+/CD24low, express cytokeratin 5 (CK5), α-smooth muscle actin (α-sma) and vimentin, known as markers of basal/myoepithelial cells; and ERα (only DuBS cells), HER1 (EGF-Receptor), activated HER2, and cyclinD1 as markers of luminal epithelial cell. Isolates of cells from breast cancer patients may be a tool for a marker-driven testing of targeted therapies.

Loss of phosphatase and tensin homolog or phosphoinositol-3 kinase activation and response to trastuzumab or lapatinib in human epidermal growth factor receptor 2-overexpressing locally advanced breast cancers

PURPOSE

Phosphatase and tensin homolog (PTEN) loss or activating mutations of phosphoinositol-3 (PI3) kinase (PIK3CA) may be associated with trastuzumab resistance. Trastuzumab, the humanized human epidermal growth factor receptor 2 (HER2) monoclonal antibody, and lapatinib, an epidermal growth factor receptor/HER2 tyrosine kinase inhibitor, are both established treatments for HER2-overexpressing breast cancers. Understanding of the cellular response to HER2-targeted therapies is needed to tailor treatments and to identify patients less likely to benefit.

METHODS

We evaluated the effect of trastuzumab or lapatinib in three HER2-overexpressing cell lines. We confirmed the in vitro observations in two neoadjuvant clinical trials in patients with HER2 overexpression; 35 patients received trastuzumab as a single agent for the first 3 weeks, then docetaxel every 3 weeks for 12 weeks (trastuzumab regimen), whereas 49 patients received lapatinib as a single agent for 6 weeks, followed by trastuzumab/docetaxel for 12 weeks before primary surgery (lapatinib regimen). Apoptosis, Ki67, p-MAPK, p-AKT, and PTEN were assessed by immunohistochemistry. Genomic DNA was sequenced for PIK3CA mutations.

RESULTS

Under low PTEN conditions, in vitro data indicate that lapatinib alone and in combination with trastuzumab was effective in decreasing p-MAPK and p-AKT levels, whereas trastuzumab was ineffective. In the clinical trials, we confirmed that low PTEN or activating mutation in PIK3CA conferred resistance to the trastuzumab regimen (P = .015), whereas low PTEN tumors were associated with a high pathologic complete response rate (P = .007).

CONCLUSION

Activation of PI3 kinase pathway is associated with trastuzumab resistance, whereas low PTEN predicted for response to lapatinib. These observations support clinical trials with the combination of both agents.

The efficacy of HER2-targeted agents in metastatic breast cancer: a meta-analysis

BACKGROUND

The addition of HER2-targeted agents to standard treatment has been shown to improve outcomes for HER2 positive metastatic breast cancer patients. We undertook a meta-analysis to evaluate the efficacy of HER2-targeted therapy in addition to standard treatment in metastatic breast cancer patients.

PATIENTS AND METHODS

Eligible trials were randomised controlled trials (RCTs) comparing the addition of HER2 therapy to standard treatment (hormone or chemotherapy) reporting overall survival (OS), time to progression (TTP), progression-free survival (PFS) and/or response rates.

RESULTS

Eight trials comprising 1848 patients were eligible for inclusion. HER2-targeted agents were trastuzumab and lapatinib and therapeutic partners were taxanes (4 RCTs), anthracyclines (1), capecitabine (2), anastrozole (1) and letrozole (1). The addition of HER2-targeted agents improved OS [hazard ratios (HR) 0.78; 95% confidence interval (CI) 0.67-0.91], TTP (HR 0.56; 95% CI 0.48-0.64), PFS (HR 0.63; 95% CI 0.53-0.74) and overall response rate (relative risk 1.67; 95% CI 1.46-1.90).

CONCLUSIONS

Our meta-analysis confirms the benefit of adding HER2-targeted therapy to standard treatment in HER2 positive metastatic breast cancer. Compared with OS, TTP, PFS and ORR overestimate treatment benefit. Trials in our meta-analysis differed in terms of partner drug or HER2 agents, yet delivered comparable outcomes.

Role of trastuzumab in the management of HER2-positive metastatic breast cancer

Breast cancer is a major health issue in developed countries. Overexpression of HER2, a member of epidermal growth factor receptor family, occurs in 20%-30% of breast cancers. HER2 drives the cancer cells to develop a more aggressive phenotype, to metastasize to viscera and central nervous system, and to be less sensitive to chemotherapeutic agents. Trastuzumab (Herceptin®) is a monoclonal antibody directed against the extracellular domain of HER2. As single agent or with chemotherapy, trastuzumab improves survival of HER2-positive breast cancers. In the past years, trastuzumab has completely revolutionized the scenario of the treatment of HER2-positive breast cancer, representing one of the most remarkable examples of targeted therapy in oncology. However, issues such as the best chemotherapeutic companion to associate with trastuzumab, cardiac toxicities, and clinical resistance still require tremendous efforts by researchers. Here, we review pharmacology, efficacy studies, and toxicities of trastuzumab in metastatic breast cancer. Moreover, we provide some insights on resistance to therapy. Finally, we briefly discuss trastuzumab's place in the clinical setting.

Deconstructing the molecular portraits of breast cancer

Breast cancer is a heterogeneous disease in terms of histology, therapeutic response, dissemination patterns to distant sites, and patient outcomes. Global gene expression analyses using high‐throughput technologies have helped to explain much of this heterogeneity and provided important new classifications of cancer patients. In the last decade, genomic studies have established five breast cancer intrinsic subtypes (Luminal A, Luminal B, HER2‐enriched, Claudin‐low, Basal‐like) and a Normal Breast‐like group. In this review, we dissect the most recent data on this genomic classification of breast cancer with a special focus on the Claudin‐low subtype, which appears enriched for mesenchymal and stem cell features. In addition, we discuss how the combination of standard clinical‐pathological markers with the information provided by these genomic entities might help further understand the biological complexity of this disease, increase the efficacy of current and novel therapies, and ultimately improve outcomes for breast cancer patients.

Fatty acid synthase phosphorylation: a novel therapeutic target in HER2-overexpressing breast cancer cells

Introduction

The human epidermal growth factor receptor 2 (HER2) is a validated therapeutic target in breast cancer. Heterodimerization of HER2 with other HER family members results in enhanced tyrosine phosphorylation and activation of signal transduction pathways. HER2 overexpression increases the translation of fatty acid synthase (FASN), and FASN overexpression markedly increases HER2 signaling, which results in enhanced cell growth. However, the molecular mechanism and regulation of HER2 and FASN interaction are not well defined. Lapatinib is a small-molecule tyrosine kinase inhibitor that blocks phosphorylation of the epidermal growth factor receptor and HER2 in breast cancer cells, resulting in apoptosis. We hypothesized that FASN is directly phosphorylated by HER2, resulting in enhanced signaling and tumor progression in breast cancer cells.

Methods

Using mass spectrometry, we identified FASN as one of the proteins that is dephosphorylated by lapatinib in SKBR3 breast cancer cells. Immunofluorescence, immunoprecipitation, Western blotting, a kinase assay, a FASN enzymatic activity assay, an invasion assay, a cell viability assay and zymography were used to determine the role of FASN phosphorylation in invasion of SKBR3 and BT474 cells. The FASN inhibitor C75 and small interfering RNA were used to downregulate FASN expression and/or activity.

Results

Our data demonstrated that FASN is phosphorylated when it is in complex with HER2. FASN phosphorylation was induced by heregulin in HER2-overexpressing SKBR3 and BT474 breast cancer cells. Heregulin-induced FASN phosphorylation resulted in increased FASN enzymatic activity, which was inhibited by lapatinib. The FASN inhibitor C75 suppressed FASN activity by directly inhibiting HER2 and FASN phosphorylation. Blocking FASN phosphorylation and activity by lapatinib or C75 suppressed the activity of matrix metallopeptidase 9 and inhibited invasion of SKBR3 and BT474 cells.

Conclusions

FASN phosphorylation by HER2 plays an important role in breast cancer progression and may be a novel therapeutic target in HER2-overexpressing breast cancer cells.

Lapatinib: new opportunities for management of breast cancer

Approximately 20% of new diagnosed breast cancers overexpress the human epidermal growth factor receptor 2 (EGFR2), also known as erythroblastic leukemia viral oncogene homolog 2 (ERBB2) protein, as a consequence of ERBB2 gene amplification, resulting in a poor prognosis. Clinical outcome can be substantially improved by ERBB2-targeted therapy. Lapatinib is a potent, orally bioavailable small molecule that reversibly and selectively inhibits epidermal growth factor receptor (EGFR1 or ERBB1) and ERBB2 tyrosine kinases. Lapatinib binds the adenosine triphosphate-binding site of the receptor's intracellular domain to inhibit tumor cell growth. This review summarizes the pharmacology, pharmacokinetics, efficacy, and tolerability of lapatinib, and reviews both Food and Drug Administration-approved and investigational uses of lapatinib in breast cancer therapy. The drug is generally well tolerated in patients, with diarrhea and rashes being the most common (usually mild or moderate) adverse effects. Unlike trastuzumab, lapatinib has infrequent adverse effects on cardiac function. Lapatinib has substantial activity for advanced ERBB2-positive breast cancer, particularly in combination with capecitabine, following progression after anthracyclines, taxanes, and trastuzumab. Lapatinib combined with capecitabine yielded significant improvements in time to progression and response rate compared with capecitabine alone. This drug can also be combined with letrozole for the treatment of postmenopausal women with ERBB2-positive breast cancer, for whom hormonal therapy is indicated. Lapatinib has shown early promise in treatment of central nervous system metastasis and is being further evaluated in various clinical settings.

Present and future evolution of advanced breast cancer therapy

Although the introduction of novel therapies and drug combinations has improved the prognosis of metastatic breast cancer, the disease remains incurable. Increased knowledge of the biology and the molecular alterations in breast cancer has facilitated the design of targeted therapies. These agents include receptor and nonreceptor tyrosine kinase inhibitors (epidermal growth factor receptor family), intracellular signaling pathways (phosphatidylinositol-3-kinase, AKT, mammalian target of rapamycin) angiogenesis inhibitors and agents that interfere with DNA repair (poly(ADP-ribose) polymerase inhibitors). In the present review, we present the most promising studies of these new targeted therapies and novel combinations of targeted therapies with cytotoxic agents.

EGFR signaling in breast cancer: bad to the bone

The epidermal growth factor receptor (EGFR) is a member of the ErbB family of receptor tyrosine kinases. This family includes EGFR/ErbB1/HER1, ErbB2/HER2/Neu ErbB3/HER3, and ErbB4/HER4. For many years it was believed that EGFR plays a minor role in the development and progression of breast malignancies. However, recent findings have led investigators to revisit these beliefs. Here we will review these findings and propose roles that EGFR may play in breast malignancies. In particular, we will discuss the potential roles that EGFR may play in triple-negative tumors, resistance to endocrine therapies, maintenance of stem-like tumor cells, and bone metastasis. Thus, we will propose the contexts in which EGFR may be a therapeutic target.

EGFR signaling in breast cancer: bad to the bone

The epidermal growth factor receptor (EGFR) is a member of the ErbB family of receptor tyrosine kinases. This family includes EGFR/ErbB1/HER1, ErbB2/HER2/Neu ErbB3/HER3, and ErbB4/HER4. For many years it was believed that EGFR plays a minor role in the development and progression of breast malignancies. However, recent findings have led investigators to revisit these beliefs. Here we will review these findings and propose roles that EGFR may play in breast malignancies. In particular, we will discuss the potential roles that EGFR may play in triple-negative tumors, resistance to endocrine therapies, maintenance of stem-like tumor cells, and bone metastasis. Thus, we will propose the contexts in which EGFR may be a therapeutic target.

Novel cytotoxic backbones and targeted therapies: recent data and ongoing clinical trials

Novel therapies are emerging for treatment of patients with localized or advanced breast cancer. Targeted therapies such as trastuzumab, lapatinib, and bevacizumab have demonstrated significant clinical benefit in the metastatic setting, and trastuzumab has also improved patient outcome as adjuvant therapy in HER2+ breast cancer. Novel chemotherapies are also being developed to improve drug delivery, enhance efficacy, or decrease drug toxicity. These novel cytotoxic agents are being combined with established targeted therapies and are showing early promise for the treatment of patients with advanced breast cancer. Finally, new targeted therapies have shown clinical benefit, either as single agents or in combination with established targeted therapy or chemotherapy.

Triple-negative breast cancer

Recent advances in biological characterization of breast cancer have eventually increased our understanding of underlying tumour biology. While for endocrine responsive and Her2-positive disease different molecular targeted therapies are available, up to now no specific targeted approach for triple-negative breast cancer has been developed. Patients with triple-negative disease are at high risk for tumour recurrence. Preclinical and limited clinical data suggest that platinum-based regimens may be the most active conventional chemotherapy, but prospective randomized trials are missing. Bevacizumab and other agents targeting tumour vessel growth have potential activity in all subtypes of breast cancer, and therefore are not considered a targeted approach for triple-negative tumours alone. Due to specific defects in DNA-damage repair, basal-like cancers depend on alternative, more error-prone repair pathways. Currently, scientific interest is focussing on drugs blocking those mechanisms. PARP-1 inhibitors, in conjunction with platinum derivatives, were found to exhibit significant survival benefit over chemotherapy alone even in a relatively small phase II study. For the first time, this approach offers the chance of highly active, specific therapy for triple-negative disease.

Quality of life in hormone receptor-positive HER-2+ metastatic breast cancer patients during treatment with letrozole alone or in combination with lapatinib

This paper presents analyses evaluating quality of life in patients with hormone receptor–positive human epidermal growth factor receptor 2–positive tumors receiving letrozole alone or in combination with lapatinib in clinical trial EGF30008.

Background.

A phase III trial compared lapatinib plus letrozole (L + Let) with letrozole plus placebo (Let) as first-line therapy for hormone receptor (HR)⁺ metastatic breast cancer (MBC) patients. The primary endpoint of progression-free survival (PFS) in patients whose tumors were human epidermal growth factor receptor (HER)-2⁺ was significantly longer for L + Let than for Let (8.2 months versus 3 months; p = .019). This analysis focuses on quality of life (QOL) in the HER-2⁺ population.

Methods.

QOL was assessed at screening, every 12 weeks, and at withdrawal using the Functional Assessment of Cancer Therapy–Breast (FACT–B). Changes from baseline were analyzed and the proportions of patients achieving minimally important differences in QOL scores were compared. Additional exploratory analyses evaluated how QOL changes reflected tumor progression status.

Results.

Among the 1,286 patients randomized, 219 had HER-2⁺ tumors. Baseline QOL scores were comparable in the two arms. Mean changes in QOL scores were generally stable over time for patients who stayed on study. The average change from baseline on the FACT-B total score in both arms was positive at all scheduled visits through week 48. There was no significant difference between the two treatment arms in the percentage of QOL responders.

Conclusion.

The addition of lapatinib to letrozole led to a significantly longer PFS interval while maintaining QOL during treatment, when compared with letrozole alone, thus confirming the clinical benefit of the combination therapy in the HR⁺ HER-2⁺ MBC patient population. This all oral regimen provides an effective option in this patient population, delaying the need for chemotherapy and its accompanying side effects.

Lapatinib plus capecitabine in women with HER-2-positive advanced breast cancer: final survival analysis of a phase III randomized trial

OBJECTIVES

A planned interim analysis of study EGF100151 prompted early termination of enrollment based on a longer time to progression with lapatinib and capecitabine than with capecitabine alone in patients with human epidermal growth factor receptor (HER)-2(+) previously treated advanced breast cancer or metastatic breast cancer (MBC). Here, we report final analyses of overall survival.

PATIENTS AND METHODS

Women with HER-2(+) MBC who progressed after regimens that included, but were not limited to, anthracyclines, taxanes, and trastuzumab, were randomized to lapatinib (1,250 mg/day) plus capecitabine (2,000 mg/m(2)) or capecitabine monotherapy (2,500 mg/m(2)) on days 1-14 of a 21-day cycle.

RESULTS

At enrollment termination, 399 patients were randomized, and nine were being screened and were offered combination treatment. In total, 207 and 201 patients were enrolled to combination therapy and monotherapy, respectively. Thirty-six patients receiving monotherapy crossed over to combination therapy following enrollment termination. The median overall survival times were 75.0 weeks for the combination arm and 64.7 weeks for the monotherapy arm (hazard ratio [HR], 0.87; 95% confidence interval [CI], 0.71-1.08; p = .210). A Cox regression analysis considering crossover as a time-dependent covariate suggested a 20% lower risk for death for patients treated with combination therapy (HR, 0.80; 95% CI, 0.64-0.99; p = .043). The low incidence of serious adverse events was consistent with previously reported rates.

CONCLUSIONS

Although premature enrollment termination and subsequent crossover resulted in insufficient power to detect differences in overall survival, exploratory analyses demonstrate a trend toward a survival advantage with lapatinib plus capecitabine. These data continue to support the efficacy of lapatinib in patients with HER-2(+) MBC.

Biological reprogramming in acquired resistance to endocrine therapy of breast cancer

Endocrine therapies targeting the proliferative effect of 17β-estradiol through estrogen receptor α (ERα) are the most effective systemic treatment of ERα-positive breast cancer. However, most breast tumors initially responsive to these therapies develop resistance through molecular mechanisms that are not yet fully understood. The long-term estrogen-deprived (LTED) MCF7 cell model has been proposed to recapitulate acquired resistance to aromatase inhibitors in postmenopausal women. To elucidate this resistance, genomic, transcriptomic and molecular data were integrated into the time course of MCF7-LTED adaptation. Dynamic and widespread genomic changes were observed, including amplification of the ESR1 locus consequently linked to an increase in ERα. Dynamic transcriptomic profiles were also observed that correlated significantly with genomic changes and were predicted to be influenced by transcription factors known to be involved in acquired resistance or cell proliferation (for example, interferon regulatory transcription factor 1 and E2F1, respectively) but, notably, not by canonical ERα transcriptional function. Consistently, at the molecular level, activation of growth factor signaling pathways by EGFR/ERBB/AKT and a switch from phospho-Ser118 (pS118)- to pS167-ERα were observed during MCF7-LTED adaptation. Evaluation of relevant clinical settings identified significant associations between MCF7-LTED and breast tumor transcriptome profiles that characterize ERα-negative status, early response to letrozole and tamoxifen, and recurrence after tamoxifen treatment. In accordance with these profiles, MCF7-LTED cells showed increased sensitivity to inhibition of FGFR-mediated signaling with PD173074. This study provides mechanistic insight into acquired resistance to endocrine therapies of breast cancer and highlights a potential therapeutic strategy.

Treatment strategy for HER2-positive breast cancer

HER2-positive tumors account for approximately 18-20% of all breast cancers. These tumors tend to be more aggressive than HER2-negative tumors and are associated with a poorer prognosis. HER2 overexpression, as determined by either 3+ immunohistochemical staining for HER2 protein or HER2 gene amplification by fluorescence in situ hybridization, should be used to select patients for anti-HER2 therapy. Trastuzumab-containing regimens as first-line therapy should be recommended to women with HER2-positive metastatic breast cancer. The continuation of trastuzumab plus capecitabine provided a significant clinical benefit compared with capecitabine alone in women who experienced progression during trastuzumab treatment. An adjuvant trastuzumab-containing regimen should be also recommended to all intermediate- or high-risk women with HER2-positive early breast cancer. Cardiac function should be serially monitored during this treatment. Many anti-HER2 drugs against breast cancer are being developed. The basic mechanisms of their action and resistance emergence are being clarified step by step. Over the mid- or long term, clinical trials comparing these drugs will be conducted until drugs that are clinically effective and easy to use in the true sense survive. Biomarkers are being aggressively searched for concerning individual drugs under development. A position of the "proper drug for the proper patient" will be more firmly established.

Through a glass darkly: advances in understanding breast cancer biology, 2000-2010

Our understanding of breast cancer as a clinical and biologic entity has been gaining granularity for several decades; in particular, the importance of hormone receptors and HER2 were realized long ago and have served as the impetus for therapeutic agents that have improved the cure rate of estrogen receptor-positive and HER2-positive breast cancer and the lives of thousands of women. The past decade brought even more understanding of the complexity of breast cancer biology through the development and clinical applications of array-based technologies for discovery and prognostication. We now realize that there are at least 5 intrinsic subtypes within breast cancer, at least one of which-the basal-like-currently lacks targeted therapies and is the most pressing therapeutic challenge for the next decade. We have several validated prognostic profiles that allow increased thoughtfulness in adjuvant decision making. With this understanding also comes the recognition that if breast cancer represents several biologically distinct entities, then breast cancer risk assessment and treatment must take this heterogeneity into account, which complicates trial design and interpretation. Despite therapeutic advances and the development of a number of targeted agents against hormone receptor signaling, HER2, and angiogenesis, we have significant challenges to overcome. These include the need for more tissue-based studies to allow us to understand the mechanisms of sensitivity and resistance within and across subtypes, and the need to revisit risk and prevention by subtype.

Combined inhibitory effect of formestane and herceptin on a subpopulation of CD44+/CD24low breast cancer cells

In breast cancer, stromal cells surrounding cancer epithelial cells can influence phenotype by producing paracrine factors. Among many mediators of epithelial-stromal interactions, aromatase activity is perhaps one of the best studied. Clinical data suggest that estrogen-independent signaling leads to increased proliferation even during therapy with aromatase inhibitors (AIs). Molecular mechanism of crosstalk between the estrogen receptor (ER) and the epidermal growth factor receptor (HER) family have been implicated in resistance to endocrine therapy, but this interaction is unclear. The ability of aromatase to induce estradiol biosynthesis provides a molecular rationale to combine agents that target aromatase activity and the HER pathway. We targeted stromal-epithelial interactions using formestane, which exerts antiaromatase activity, combined with the monoclonal anti-HER2 antibody herceptin, in a subpopulation of CD44+/CD24low cells sorted from epithelial-mesenchymal co-cultures of breast cancer tissues. The growth inhibition was respectively 16% (P < 0.01) in the response to herceptin, 25% to formestane (P < 0.01), and 50% (P < 0.001) with the combination of the two drugs, suggesting that herceptin cooperates with formestane-induced inhibition of aromatase and this effect could be mediated through HER family receptors. In cells which expressed ERalpha, formestane/herceptin combination suppressed the mRNA expression of aromatase and HER2 and decreased cyclin D1 expression. These results show that combination therapies involving AIs and anti-HER2 can be efficacious for the treatment of cancer in experimental models and suggest that subtyping breast tumors gives useful information about response to treatment.

Small HER2-positive, node-negative breast cancer: who should receive systemic adjuvant treatment?

Adjuvant treatment of early-stage breast cancer with combined trastuzumab and chemotherapy has become standard in patients with HER2-positive tumors and a diameter of >1 cm or positive lymph nodes. Currently, there are no data directly supporting the use of adjuvant treatment, including trastuzumab, in patients with HER2-positive tumors, a diameter of ≤1 cm and no nodal involvement (pT1a,bpN0M0). However, 6%-10% of these small tumors are HER2 positive, and there is good evidence for an inferior clinical outcome in these patients, with recurrence rates of up to 30% after 5-10 years. Assumed that the relative risk reduction is similar to larger tumors, the absolute benefit should be large enough to consider adjuvant treatment. This review addresses current data regarding the prognosis of small HER2-positive tumors and discusses potential factors to individualize adjuvant treatment in patients with small HER2-positive tumors.

The Role of Targeted Agents in the Treatment of Metastatic Breast Cancer

To date, blockade of growth factor receptors is the mainstay of targeted therapy in metastatic breast cancer (mBC). Monoclonal antibodies such as trastuzumab and bevacizumab represent the first generation of molecular-based therapies. Both the HER2 inhibitors and the vascular endothelial growth factor (VEGF) antagonists have shown synergism with a broad spectrum of established cytotoxins, thus being approved for first-line treatment of mBC in combination with taxanes. As a next step, tyrosine kinase inhibitors (TKIs) have been integrated into daily routine as an alternative approach for targeting HER2: The dual HER1/2 inhibitor lapatinib demonstrated activity in trastuzumab-pretreated mBC patients in combination with capecitabine. Furthermore, chemotherapy-free regimens (trastuzumab or lapatinib plus aromatase inhibitors) have been identified as additional options for hormone receptor (HR)- and HER2-positive patients. Recently published data indicate that a combination of two biologicals such as lapatinib and trastuzumab can be effective as a treatment beyond trastuzumab related progression. Multitarget TKIs have the potential to inhibit several signaling pathways involved in breast cancer-related angiogenesis. Until now, they have failed to show a clear benefit in mBC. On the other hand, poly(ADP-ribose) polymerase (PARP) inhibition, mediated by a new class of small molecules, is an interesting area of investigation. Future directions of research in HER2-positive breast cancer focus on the evaluation of novel antibodies (pertuzumab, T-DM1), and irreversible TKIs (neratinib, BIBW 2992) and inhibitors of HER2-related downstream signaling (mTOR, TORC 1/2, PI3K/Akt) and of receptor cross-talk (IGFR).

Management of ErbB2-positive breast cancer: insights from preclinical and clinical studies with lapatinib

The management of human epidermal growth factor receptor 2-positive (ErbB2+) breast cancer is challenging; patients with ErbB2+ breast tumors have more aggressive disease and a poor prognosis. The increasing incidence of breast cancer in Asia and the limitations of existing treatments pose additional challenges. In this review, we summarize the preclinical and clinical evidence that indicates how lapatinib, a novel inhibitor that targets the human epidermal growth factor receptor (ErbB1) and ErbB2 may help clinicians address four particularly challenging issues in the management of ErbB2+ breast cancer. These issues are: (i) trastuzumab therapy failure, (ii) development of central nervous system metastases, (iii) minimizing toxicity and (iv) selecting the most appropriate partners (chemotherapy and non-chemotherapy) for combination therapy with lapatinib. Lapatinib, in combination with chemotherapeutic agents, such as capecitabine, provides clinical benefits to patients with ErbB2+ breast cancer, including patients who develop progressive disease on trastuzumab. Lapatinib, in combination with non-chemotherapeutic agents, such as letrozole, may also provide a chemotherapy-free treatment option for postmenopausal patients with estrogen receptor-positive/ErbB2+ metastatic breast cancer. Encouraging results have also emerged regarding the synergistic effects of lapatinib in combination with other agents for the treatment of ErbB2+ breast cancer. Promising findings have also been reported for the use of lapatinib to prevent and treat central nervous system metastases. Collectively, these results indicate that the judicious use of lapatinib, an effective oral therapy with a manageable toxicity profile, can enhance the management of patients with ErbB2+ breast cancer.

Emerging targeted therapies for breast cancer

Increased understanding of the molecular events involved in cancer development has led to the identification of a large number of novel targets and, in parallel, to the development of multiple approaches to anticancer therapy. Targeted therapy focuses on specific molecules in the malignant cell signal transduction machinery, including crucial molecules involved in cell invasion, metastasis, apoptosis, cell-cycle control, and tumor-related angiogenesis. In breast cancer, two new targeted agents have recently been approved: lapatinib, directed against the human epidermal growth factor receptor 2 (HER2); and bevacizumab, directed against vascular endothelial growth factor (VEGF). Multiple other targeted agents are under evaluation in clinical trials, including inhibitors of the epidermal growth factor receptor (EGFR), dual EGFR and HER2 inhibitors, other VEGF or VEGF-receptor inhibitors, and agents that alter crucial signaling pathways, such as RAS/MEK/ERK; phosphatidylinositol-3-kinase/Akt/ mammalian target of rapamycin; insulin-like growth factor/insulin-like growth factor receptor; poly (ADP-ribose) polymerase 1; and others. In this review, we present the most promising studies of these new targeted therapies and novel combinations of targeted therapies with traditional cytotoxic agents.

Molecular basis for therapy resistance

Chemoresistance remains the main reason for therapeutic failure in breast cancer as well as most other solid tumours. While gene expression profiles related to prognosis have been developed, so far use of such signatures as well as single markers has been of limited value predicting drug resistance. Novel technologies, in particular with regard to high through-put sequencing holds great promises for future identification of the key "driver" mechanisms guiding chemosensitivity versus resistance in breast cancer as well as other malignant conditions.

Lapatinib in the Treatment of Hormone Receptor-Positive/ErbB2-Positive Breast Cancer

SUMMARY: In women with estrogen receptor(ER)- and ErbB2 (HER2)-positive breast cancer, a vicious cycle is established between ER mechanisms of action and the growth factor receptor network, leading to enhanced cell proliferation and endocrine resistance. As such, co-targeting ErbB1 and ErbB2 with lapatinib in combination with hormonal therapy is an attractive approach to enhance the efficacy of either tamoxifen or estrogen deprivation. As demonstrated in the EGF30008 trial, a combined targeted strategy with letrozole and lapatinib significantly increased progression-free survival and clinical benefit rates in patients with metastatic breast cancer that co-expresses ER and ErbB2. Therefore, women who are not in an acutely life-threatening situation should be considered for upfront treatment with hormonal therapy (e.g. aromatase inhibitors) in combination with an anti-ErbB2 therapy.

Quality-of-life and quality-adjusted survival (Q-TWiST) in patients receiving lapatinib in combination with paclitaxel as first-line treatment for metastatic breast cancer

BACKGROUND

In a phase 3 randomized, multicenter, double-blind, placebo-controlled study, first-line therapy with lapatinib plus paclitaxel significantly improved clinical outcomes based on a pre-planned analysis of ErbB2+ metastatic breast cancer patients (GSK Study #EGF30001; ClinicalTrials.gov identifier: NCT00075270). Patients with ErbB2- or untested did not significantly benefit. This article focuses on the quality of life (QOL) and quality-adjusted survival outcomes (Q-TWiST) in the study.

METHODS

QOL was assessed using the Functional Assessment of Cancer Therapy-Breast (FACT-B). Changes from baseline were analyzed using ANCOVAs, repeated measures and pattern mixture modeling. The Q-TWiST method was used to examine the trade-off between toxicities and delayed progression.

RESULTS

The study included 579 subjects, of whom 86 were ErbB2+. In the ITT population, no significant differences in QOL or Q-TWiST scores were observed. In the ErbB2+ subgroup, the lapatinib plus paclitaxel (L + P) arm demonstrated stable FACT-B scores over the first year, while average scores for patients on P + placebo (P + pla) monotherapy decreased (change from baseline: L + P, p = 0.99; P + pla, p = 0.01). Clinically meaningful differences were observed between treatment arms on the FACT-B, Trial Outcome Index and breast cancer subscale scores. Pattern mixture models suggested more QOL differentiation between treatments among patients who progressed or withdrew early. Q-TWiST differences between the arms in the ErbB2+ subgroup ranged from 2 to 15 weeks with an L + P advantage across all utility weight combinations.

CONCLUSIONS

In the ITT population, results provide no evidence of QOL differences between treatment groups. In a small, prospectively-defined subgroup of ErbB2+ patients, L + P resulted in more stable QOL and more quality-adjusted survival than paclitaxel monotherapy, representing clinically important differences between treatments.

New strategies in estrogen receptor-positive breast cancer

Endocrine therapy has led to a significant improvement in outcomes for women with estrogen receptor-positive (ER+) breast cancer. Current questions in the adjuvant setting include the optimal duration of endocrine therapy, and the accurate molecular prediction of endocrine responsiveness using gene array-based assays compared with ER expression itself. In advanced disease, novel selective estrogen receptor antagonists (SERM) have failed to make an impact, although the pure ER antagonist fulvestrant may have a role, albeit optimal dose and sequence remain unclear. Overcoming de novo or acquired endocrine resistance remains critical to enhancing further the benefit of existing endocrine therapies. Recent progress has been made in understanding the molecular biology associated with acquired endocrine resistance, including adaptive "cross-talk" between ER and peptide growth factor receptor pathways such as epidermal growth factor receptor (EGFR)/human epidermal growth factor receptor 2 (HER2). Future strategies that are being evaluated include combining endocrine therapy with inhibitors of growth factor receptors or downstream signaling pathways, to treat or prevent critical resistance pathways that become operative in ER+ tumors. Preclinical experiments have provided great promise for this approach, although clinical data remain mixed. Enriching trial recruitment by molecular profiling of different ER+ subtypes will become increasingly important to maximize additional benefit that new agents may bring to current endocrine therapies for breast cancer.

Phase II, randomized trial to compare anastrozole combined with gefitinib or placebo in postmenopausal women with hormone receptor-positive metastatic breast cancer

PURPOSE

This phase II randomized trial evaluated the efficacy and tolerability of anastrozole combined with gefitinib or anastrozole with placebo in women with hormone receptor-positive metastatic breast cancer (MBC).

EXPERIMENTAL DESIGN

Postmenopausal women with hormone receptor-positive measurable or evaluable MBC who had not received prior endocrine therapy for this disease stage or who developed metastatic disease during/after adjuvant tamoxifen were eligible. The primary response variable was progression-free survival (PFS) and secondary response variables included clinical benefit rate, objective response rate, overall survival, safety and tolerability, and pharmacokinetics. Tumor biomarker evaluation was an exploratory objective.

RESULTS

Forty-three patients were randomized to anastrozole plus gefitinib and 50 patients were randomized to anastrozole plus placebo of a planned total of 174 patients (enrollment was prematurely discontinued due to slow recruitment). PFS for patients receiving the combination of anastrozole and gefitinib was longer than for patients receiving anastrozole plus placebo [hazard ratio (gefitinib/placebo), 0.55; 95% confidence interval, 0.32-0.94; median PFS, 14.7 versus 8.4 months]. The clinical benefit rate was 49% versus 34%, and the objective response rate was 2% versus 12% with anastrozole plus gefitinib and anastrozole plus placebo, respectively. No evidence of interaction between baseline biomarker levels and relative treatment effect was found. No unexpected adverse events were observed.

CONCLUSION

This small randomized study showed that anastrozole in combination with gefitinib is associated with a marked advantage in PFS compared with anastrozole plus placebo, and that the combination was tolerated in postmenopausal women with hormone receptor-positive MBC. Further investigation of epidermal growth factor receptor inhibition in combination with endocrine therapy may be warranted.

Lapatinib restores hormone sensitivity with differential effects on estrogen receptor signaling in cell models of human epidermal growth factor receptor 2-negative breast cancer with acquired endocrine resistance

PURPOSE

Acquired endocrine resistance in estrogen receptor (ER)alpha+/human epidermal growth factor receptor 2-negative (HER2-) breast cancer has been associated with modest adaptive increases in HER2, although exactly how aberrant HER2 signaling affects the ERalpha pathway is poorly understood. We investigated (a) whether the epidermal growth factor receptor/HER2 inhibitor lapatinib could restore endocrine responsiveness in cell models of acquired endocrine resistance with modest increases in HER2, and (b) the nature of ERalpha-HER2 cross-talk in this process.

METHODS

Combination growth studies, ERalpha transcription, immunoblot, and gene expression assays were conducted in two models of acquired resistance to (a) estrogen deprivation (long-term estrogen-deprived cells) and (b) tamoxifen (long-term tamoxifen-treated cells), and in hormone sensitive controls. Changes in ERalpha, PgR, and HER2 were assessed in samples from patients treated with tamoxifen.

RESULTS

Both cell models of acquired endocrine resistance showed modest adaptive upregulation in HER2, and lapatinib restored endocrine sensitivity in both. The effect of lapatinib on ERalpha signaling varied markedly depending on the nature of the HER2/ERalpha cross-talk. In long-term estrogen-deprived cells characterized by enhanced ERalpha function, lapatinib suppressed ERalpha genomic activity (as measured by pERSer118, ERalpha transcriptional activity, and PGR gene expression). In contrast, in long-term tamoxifen-treated cells with reduced ERalpha activation, lapatinib reactivated ERalpha genomic function. Twenty percent of tamoxifen-resistant patients relapsed with modest increases in HER2 and either suppressed or enhanced ERalpha/PgR expression.

CONCLUSIONS

Aberrant GFR signaling can augment or suppress ERalpha function. Regardless, interrupting the HER2/ERalpha cross-talk with lapatinib can restore endocrine sensitivity and should be investigated as a therapeutic strategy in combination with endocrine therapy in ERalpha+/HER2- patients with acquired endocrine resistance.

Does lapatinib work against HER2-negative breast cancers?

Aberrant growth factor receptor signaling can augment or suppress estrogen receptor (ER) function in hormone-dependent breast cancer cells and lead to escape from anti-estrogen therapy. Interruption of HER2/ER cross-talk with lapatinib can restore sensitivity to anti-estrogens and thus, should be investigated in combination with endocrine therapy in patients with ER+/HER2-negative breast cancers.