Hormonal treatment combined with targeted therapies in endocrine-responsive and HER2-positive metastatic breast cancer

Approximately 50% of HER2 positive breast cancer cases are also estrogen receptor (ER) positive. Data supports a role for close cross-talk between the ER and HER2 signaling pathways as an important contributor to the development of de novo or acquired resistance to hormone therapies. Therefore a strategy that simultaneously blocks both signaling pathways is a reasonable approach to prevent or overcome either endocrine or anti-HER2 therapy resistance. Moreover, preclinical data support the idea that PI3K inhibitors and CDK4/6 could be an attractive target that functions downstream of both ER and HER2 pathways. We conducted a literature review of the results of phase II and III studies testing targeted therapies in metastatic breast cancer with HER2-positive and hormonal-receptor-positive disease. The analyses included efficacy and toxicity data from earlier studies with a single anti-HER2 drug combined with hormonal therapy up to more recent studies testing new molecules targeting these signaling pathways. The aims of this review are to summarize current knowledge and to discuss research development including the possibility to spare chemotherapy in this subgroup of HER2-positive breast cancer patients.

Targeted therapies in breast cancer: are heart and vessels also being targeted?

The concept of 'targeted' therapies implies that such drugs only act on cells that specifically express the particular target, therefore giving rise to a low incidence of side effects. However, targeted therapies currently approved for the treatment of breast cancer have demonstrated a relatively high incidence of cardiovascular events. The anti-HER2 agents trastuzumab and lapatinib may cause left ventricular dysfunction or even congestive heart failure. Bevacizumab, an antiangiogenic drug, has been shown to increase the risk of hypertension, cardiovascular dysfunction and thromboembolic events. In addition, several anti-human epidermal growth factor receptor 2 (HER2) and antiangiogenic agents plus their combinations are currently being developed and evaluated for the treatment of breast cancer. In this review, we aim to assess the incidence of cardiac adverse events associated with targeted therapies designed to block HER2 and angiogenic pathways.

Optimizing chemotherapy-free survival for the ER/HER2-positive metastatic breast cancer patient

The recent incremental advances made in the treatment of metastatic breast cancer have elicited potential for survival extension in this treatable, yet incurable, population of breast cancer patients. Clinicians have focused on targeted therapies, which aim at signaling receptors such as the human epidermal receptor superfamily, the estrogen receptor, VEGF, the insulin-like growth factor receptor, the hepatocyte growth factor receptor (cMET), phosphoinositide 3-kinase, mTOR, and many others.

Antiangiogenic strategies in breast cancer management

Angiogenesis is considered one of the key mechanisms of tumour growth and survival. Therefore it represents an ideal pharmaceutical target. Many antiangiogenic agents have been developed so far in several solid tumours and also in breast cancer. Vascular endothelial growth factor (VEFG) is the main target and both monoclonal antibodies and small molecules belonging to the tyrosine kinase inhibitors directed against VEGF(R) have been developed. Some other therapeutic approaches have shown to exert some antiangiogenic activity, such as hormonal agents, metronomic chemotherapy, bisphosphonates and others. In this paper we provide an introduction of the current data supporting the angiogenesis in breast cancer and a review of the most relevant antiagiogenic therapies which have been investigated so far.

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.

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.

Novel therapeutic approaches to the treatment of metastatic breast cancer

Metastatic breast cancer is ultimately an incurable disease, although recent data have shown that its incidence is decreasing and that patients with metastatic breast cancer live longer. This improvement in survival seems to be linked with the introduction of new therapeutic agents, novel combinations of existing therapies and targeted therapies. Our increasing understanding of the molecular biology of metastatic disease has allowed the development of therapies aimed at specific molecular targets. Some of these have already been approved for the treatment of metastatic breast cancer in combination with cytotoxics, and others have shown promising results regarding disease-free survival, overall response rates and time to disease progression. Given the enormous amount of information about drug discovery in cancer, it is important to be familiar with the present state of the treatment of metastatic breast cancer. The purpose of this review is to provide an update on the development of some of the most promising novel agents and treatment strategies in metastatic breast cancer.

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

PURPOSE

Cross-talk between human epidermal growth factor receptors and hormone receptor pathways may cause endocrine resistance in breast cancer. This trial evaluated the effect of adding lapatinib, a dual tyrosine kinase inhibitor blocking epidermal growth factor receptor and human epidermal growth factor receptor 2 (HER2), to the aromatase inhibitor letrozole as first-line treatment of hormone receptor (HR) -positive metastatic breast cancer (MBC).

PATIENTS AND METHODS

Postmenopausal women with HR-positive MBC were randomly assigned to daily letrozole (2.5 mg orally) plus lapatinib (1,500 mg orally) or letrozole and placebo. The primary end point was progression-free survival (PFS) in the HER2-positive population. Results In HR-positive, HER2-positive patients (n = 219), addition of lapatinib to letrozole significantly reduced the risk of disease progression versus letrozole-placebo (hazard ratio [HR] = 0.71; 95% CI, 0.53 to 0.96; P = .019); median PFS was 8.2 v 3.0 months, respectively. Clinical benefit (responsive or stable disease >or= 6 months) was significantly greater for lapatinib-letrozole versus letrozole-placebo (48% v 29%, respectively; odds ratio [OR] = 0.4; 95% CI, 0.2 to 0.8; P = .003). Patients with centrally confirmed HR-positive, HER2-negative tumors (n = 952) had no improvement in PFS. A preplanned Cox regression analysis identified prior antiestrogen therapy as a significant factor in the HER2-negative population; a nonsignificant trend toward prolonged PFS for lapatinib-letrozole was seen in patients who experienced relapse less than 6 months since prior tamoxifen discontinuation (HR = 0.78; 95% CI, 0.57 to 1.07; P = .117). Grade 3 or 4 adverse events were more common in the lapatinib-letrozole arm versus letrozole-placebo arm (diarrhea, 10% v 1%; rash, 1% v 0%, respectively), but they were manageable.

CONCLUSION

This trial demonstrated that a combined targeted strategy with letrozole and lapatinib significantly enhances PFS and clinical benefit rates in patients with MBC that coexpresses HR and HER2.

Tumoral angiogenesis and breast cancer

Breast cancer (BC) is the most common neoplasm in women in Western countries. Tumoral angiogenesis (TA) is essential for the growth and spread of BC cells. There are at least 6 different angiogenic growth factors associated with TA in BC. The major mediator of TA is vascular endothelial growth factor (VEGF), a homodimeric heparin-binding glycoprotein. VEGF signals through VEGF receptor-2 (VEGFR-2), the major VEGF signalling receptor that mediates sprouting angiogenesis. Recently, different antiangiogenic agents have shown efficacy in the treatment of advanced BC. Bevacizumab, a humanised monoclonal antibody against VEGF, in combination with taxanes improves progression-free survival and overall response rate in first-line therapy. Other new antiangiogenic agents, called multi-kinase inhibitors (sunitinib and pazopanib), are under investigation. Finally, a schedule of treatment called metronomic chemotherapy, with antiangiogenic activity, has also demonstrated efficacy in the treatment of advanced BC.

Tolerability of and adherence to combination oral therapy with gefitinib and capecitabine in metastatic breast cancer

PURPOSE

This phase I study explored gefitinib (G) and capecitabine (C) in metastatic breast cancer (MBC).

METHODS

Sequential cohorts (n = 3) received G and escalating C on a 14 day on/7 day off schedule, with a validation cohort (n = 10) at the maximum tolerated dose (MTD). Dose limiting toxicity (DLT) was defined in cycle 1. The primary endpoint was safety; secondary endpoints included response and adherence.

RESULTS

About 19 patients were treated for a median of 5 cycles. No patients in sequential cohorts experienced DLT; C MTD was 2,000 mg/m(2)/day when paired with daily G 250 mg. In the validation cohort, four experienced serious toxicities, including diarrhea, mucositis, and palmarplantar dysesthesia. At the MTD, 6 (46%) required a C dose reduction, and 3 (23%) came off study for toxicity. One partial response was observed (8%, 95% CI 0.2-38.5%); five had stable disease >24 weeks (26, 95% CI 9-51%). Patients missed few drug doses, with the suggestion of overadherence to therapy.

CONCLUSIONS

In this phase I study of G and C in MBC, a C MTD was identified, and significant toxicity was observed. About 8% demonstrated a response, with 26% maintaining stable disease. The possibility of overadherence, as suggested in this study, may have implications for other trials of oral antineoplastic therapy.

Biologic therapy of breast cancer: focus on co-inhibition of endocrine and angiogenesis pathways

There remains a high unmet need for effective treatments for metastatic breast cancer. In recent years there have been many advances in the understanding of biological basis of cancer. Several cellular pathways have been identified that play crucial roles in causing or maintaining the cancer phenotype. Many new agents that target these pathways have entered the clinic or are being investigated. In order to improve the therapeutic efficacy seen with single-agent regimens, rational combinations of targeted agents are being evaluated in ongoing trials. The optimal sequencing and combination of agents has yet to be established. Endocrine and vascular endothelial growth factor pathways are the two most prominent pathways active in breast cancer cells and inhibition of either of these is associated with clinical benefit. Here we discuss the rationale for simultaneously targeting these pathways and highlight ongoing clinical trials.