Everolimus plus exemestane for hormone-receptor-positive, human epidermal growth factor receptor-2-negative advanced breast cancer: overall survival results from BOLERO-2†

Management of locally advanced breast cancer-perspectives and future directions

Locally advanced breast cancer (LABC) constitutes a heterogeneous entity that includes advanced-stage primary tumours, cancers with extensive nodal involvement and inflammatory breast carcinomas. Although the definition of LABC can be broadened to include some large operable breast tumours, we use this term to strictly refer to inoperable cancers that are included in the above-mentioned categories. The prognosis of such tumours is often unfavourable; despite aggressive treatment, many patients eventually develop distant metastases and die from the disease. Advances in systemic therapy, including radiation treatment, surgical techniques and the development of new targeted agents have significantly improved clinical outcomes for patients with this disease. Notwithstanding these advances, LABC remains an important clinical problem, particularly in developing countries and those without widely adapted breast cancer awareness programmes. The optimal management of LABC requires a multidisciplinary approach, a well-coordinated treatment schedule and close cooperation between medical, surgical and radiation oncologists. In this Review, we discuss the current state of the art and possible future treatment strategies for patients with LABC.

Evaluating the pharmacokinetics and pharmacodynamics of everolimus for treating breast cancer

INTRODUCTION

The aberrant activation of the phosphoinositide 3-kinase-Akt-mTOR signaling pathway is a common mechanism of resistance to endocrine therapy and human epidermal growth factor receptor 2 (HER2)-targeted treatments in breast cancer. Data from large clinical trials have shown that the combination of everolimus , an orally bioavailable mTOR inhibitor with exemestane improves outcome of metastatic breast cancer resistant to non-steroidal aromatase inhibitors. On the other hand, the addition of everolimus to trastuzumab in order to overcome resistance did not show meaningful clinical benefit in recent reported Phase III clinical trials. Everolimus has a favorable pharmacokinetic (PK) profile in early breast cancer studies. The association of endocrine therapy and HER2-targeted agents did not influence the main PK parameters of the drugs.

AREAS COVERED

This review article focuses on the biological rationale of using everolimus in breast cancer and on latest advances in the field of everolimus-based combinations with an emphasis on the PK and pharmacodynamic parameters of the drug throughout different studies.

EXPERT OPINION

Better identification of patients who sustain benefit or who are resistant to everolimus-based combinations in the treatment of advanced breast cancer remains an unmet need. New combination strategies based on the understanding of resistance mechanisms and intracellular feedback loops should be studied further in the future.

Mechanisms of hormonal therapy resistance in breast cancer

Whilst estrogen receptor (ER)-positive breast cancers are preferentially treated with hormone therapy, approximately one-third of them relapse. The mechanisms of refractoriness have been investigated by numerous studies but have not been fully clarified. Hormonal therapy resistance, particularly aromatase inhibitor (AI) resistance, may be related to the acquisition of alternative intracellular ER signaling. We have been investing the mechanisms using cancer specimens and cell lines by monitoring the transcription activity of ERs. AI refractory specimens showed diverse ER activity in the adenovirus estrogen receptor element-green fluorescent protein (ERE-GFP) assay and varied sensitivity to anti-estrogens, indicating the existence of multiple resistant mechanisms. We established six different types of cell lines mimicking AI resistance from ERE-GFP-introduced ER-positive cell lines. They revealed that multiple and alternative ER activating pathways were involved in the resistance, such as phosphorylation-dependent or androgen metabolite-dependent mechanisms. The response to fulvestrant and mammalian target of rapamycin inhibitor also varied among individual resistant cell lines. These results indicate that further subclassification of ER-positive breast cancer is extremely important to decide the therapeutic management of not only hormonal therapy but also new molecular target therapy.

Novel agents and associated toxicities of inhibitors of the pi3k/Akt/mtor pathway for the treatment of breast cancer

The pi3k/Akt/mtor (phosphatidylinositol 3 kinase/ Akt/mammalian target of rapamycin) signalling pathway is an established driver of oncogenic activity in human malignancies. Therapeutic targeting of this pathway holds significant promise as a treatment strategy. Everolimus, an mtor inhibitor, is the first of this class of agents approved for the treatment of hormone receptor-positive, human epidermal growth factor receptor 2-negative advanced breast cancer. Everolimus has been associated with significant improvements in progression-free survival; however, it is also associated with increased toxicity related to its specific mechanism of action.

METHODS

A comprehensive review of the literature conducted using a focused medline search was combined with a search of current trials at http://ClinicalTrials.gov/. Summary tables of the toxicities of the various classes of pi3k/Akt/mtor inhibitors were created. A broad group of Canadian health care professionals was assembled to review the data and to produce expert opinion and summary recommendations for possible best practices in managing the adverse events associated with these pathway inhibitors.

RESULTS

Differing toxicities are associated with the various classes of pi3k/Akt/mtor pathway inhibitors. The most common unique adverse events observed in everolimus clinical trials in breast cancer include stomatitis (all grades: approximately 60%), noninfectious pneumonitis (15%), rash (40%), hyperglycemia (15%), and immunosuppression (40%). To minimize grades 3 and 4 toxicities and to attempt to attain optimal outcomes, effective management of those adverse events is critical. Management should be interdisciplinary and should use approaches that include education, early recognition, active intervention, and potentially prophylactic strategies.

DISCUSSION

Everolimus likely represents the first of many complex oral targeted therapies for the treatment of breast cancer. Using this agent as a template, it is essential to establish best practices involving and integrating multiple disciplines for the management of future pi3k/Akt/mtor signalling pathway inhibitors.

A new era of improving progression-free survival with dual blockade in postmenopausal HR(+), HER2(-) advanced breast cancer

Disease progression despite existing endocrine therapies remains a major challenge to the effective management of hormone-receptor-positive (HR(+)), human epidermal growth factor receptor-2-negative (HER2(-)), advanced breast cancer. Recent advances in elucidating the molecular mechanisms of disease progression have identified the existence of adaptive "cross-talk" between the estrogen receptor (ER) and various growth factor receptor and intracellular signaling pathways, allowing breast cancer cells to escape the inhibitory effects of endocrine therapy. These findings provide the clinical rationale for enhancing or extending endocrine sensitivity by combining endocrine therapy with a targeted agent against a compensatory pathway. In BOLERO-2, adding the mTOR inhibitor everolimus to endocrine therapy significantly improved progression-free survival (PFS) in patients with HR(+) advanced breast cancer previously treated with nonsteroidal aromatase inhibitor therapy. Notably, PFS benefits were comparable in subgroup analyses of first- and later-line settings. These results contrast with those of the large first-line HORIZON study, wherein adding the mTOR inhibitor temsirolimus to endocrine therapy did not improve PFS. Therefore, it is unclear whether a targeted agent should only be combined with endocrine therapy to restore endocrine sensitivity or whether it may also prevent or delay resistance in hormone-sensitive advanced breast cancer. Numerous additional targeted agents are currently being evaluated in combination with endocrine therapies, including PI3K, cyclin-dependent kinase 4/6, SRC, and histone deacetylase inhibitors. Appropriate patient selection based on prior treatment history will become increasingly important in maximizing the incremental benefit derived from these new agents combined with existing endocrine therapies in HR(+) advanced breast cancer.

A phase II trial of everolimus, temozolomide, and radiotherapy in patients with newly diagnosed glioblastoma: NCCTG N057K

BACKGROUND

The mammalian target of rapamycin (mTOR) functions within the phosphatidylinositol-3 kinase (PI3K)/Akt pathway as a critical modulator of cell survival. This clinical trial evaluated the combination of the mTOR inhibitor everolimus with conventional temozolomide (TMZ)-based chemoradiotherapy.

METHODS

Newly diagnosed patients with glioblastoma multiforme were eligible for this single arm, phase II study. Everolimus (70 mg/wk) was started 1 week prior to radiation and TMZ, followed by adjuvant TMZ, and continued until disease progression. The primary endpoint was overall survival at 12 months, and secondary endpoints were toxicity and time to progression. Eleven patients were imaged with 3'-deoxy-3'-(18)F-fluorothymidine ((18)FLT)-PET/CT before and after the initial 2 doses of everolimus before initiating radiation/TMZ. Imaged patients with sufficient tumor samples also underwent immunohistochemical and focused exon sequencing analysis.

RESULTS

This study accrued 100 evaluable patients. Fourteen percent of patients had grade 4 hematologic toxicities. Twelve percent had at least one grade 4 nonhematologic toxicity, and there was one treatment-related death. Overall survival at 12 months was 64% and median time to progression was 6.4 months. Of the patients who had (18)FLT-PET data, 4/9 had a partial response after 2 doses of everolimus. Focused exon sequencing demonstrated that (18)FLT-PET responders were less likely to have alterations within the PI3K/Akt/mTOR or tuberous sclerosis complex/neurofibromatosis type 1 pathway compared with nonresponders.

CONCLUSION

Combining everolimus with conventional chemoradiation had moderate toxicity. (18)FLT-PET studies suggested an initial antiproliferative effect in a genetically distinct subset of tumors, but this did not translate into an appreciable survival benefit compared with historical controls treated with conventional therapy.

Cost-effectiveness analysis of everolimus plus exemestane versus exemestane alone for treatment of hormone receptor positive metastatic breast cancer

Everolimus in combination with exemestane significantly improved progression-free survival compared to exemestane alone in patients previously treated with non-steroidal aromatase inhibitors in the BOLERO-2 trial. As a result, this combination has been approved by the food and drug administration to treat postmenopausal women with hormone receptor positive and HER2 negative metastatic breast cancer. A cost-effectiveness analysis was conducted to determine whether everolimus represents good value for money, utilizing data from BOLERO-2. A decision-analytic model was used to estimate the incremental cost-effectiveness ratio between treatment arms of the BOLERO-2 trial. Costs were obtained from the Center for Medicare Services drug payment table and physician fee schedule. Benefits were expressed as quality-adjusted progression-free survival weeks (QAPFW) and quality-adjusted progression-free years (QAPFY), with utilities/disutilities derived from the literature. Deterministic and probabilistic sensitivity analyses were performed. A willingness to pay threshold of 1-3 times the per capita gross domestic product was adopted, as per the definition of the World Health Organization. The U.S. per capita gross domestic product in 2013 was $49,965; thus, a threshold varying between $49,965 and $149,895 was considered. Everolimus/exemestane had an incremental benefit of 11.88 QAPFW (0.22 QAPFY) compared to exemestane and an incremental cost of $60,574. This translated into an ICER of $265,498.5/QAPFY. Univariate sensitivity analyses showed important variations of the ICER, ranging between $189,836.4 and $530,947/QAPFY. A tornado analysis suggested that the key drivers of our model, by order of importance, included health utility value for stable disease, everolimus acquisition costs, and transition probabilities from the stable to the progression states. The Monte-Carlo simulation showed results that were similar to the base-case analysis. This cost-effectiveness analysis showed that everolimus plus exemestane is not cost-effective compared to exemestane alone. Further research is needed to investigate the cost-effectiveness of the drug combination within sub-groups of the population studied in BOLERO-2.