Hormone receptor positive, HER2 negative metastatic breast cancer: Impact of CDK4/6 inhibitors on the current treatment paradigm.

Resistance to endocrine therapy is a significant therapeutic challenge in the treatment of women with hormone receptor positive (HR+), human epidermal growth factor receptor 2 negative (HER2-) advanced breast cancer. Cyclin-dependent kinase (CDK)4/6 inhibitors in combination with endocrine therapy have been shown to improve progression free survival, overall response rate and clinical benefit rate in women with HR+ HER2- metastatic breast cancer compared with endocrine therapy alone. This review examines the clinical evidence to support the use of CDK4/6 inhibitors in first and second line settings. Practical guidance is provided for the use of CDK4/6 inhibitors, including tolerability data, monitoring requirements and management of key toxicities for each of the available agents.

Hormone receptor positive, HER2 negative metastatic breast cancer: A systematic review of the current treatment landscape.

Endocrine therapy for the treatment of hormone receptor positive, HER2 negative, metastatic breast cancer is continually evolving. We systematically reviewed phase 2 and 3 randomized controlled trials (RCTs) of agents used in this setting to assess the effectiveness and safety of these agents for postmenopausal women. Across the 32 studies in more than 10,000 patients, the greatest improvement in progression-free survival (PFS) was seen with the addition of a cyclin-dependent kinase (CDK)4/6 inhibitor to standard endocrine therapy. Treatment with a mammalian target of rapamycin (mTOR) inhibitor, phosphoinositol-3-kinase (Pi3K) inhibitor, vascular endothelial growth factor (VEGF) inhibitor and with a selective estrogen receptor degrader (SERD) also showed benefit in PFS for selected trials. Overall survival (OS) improved with the use of mTOR inhibitors and a SERD; however, studies were not powered for an OS endpoint. Encouraging results from early studies of histone deacetylase (HDAC) and B-cell lymphoma (BCL2) inhibitors are yet to be confirmed in phase III clinical trials. Study discontinuation rates and toxicity-related deaths were highest with VEGF inhibitors in combination with endocrine therapy, limiting their use in hormone receptor positive breast cancer. CDK4/6 inhibitors and mTOR inhibitors appeared to have activity in both first and second line settings, but required additional monitoring for common toxicities. The activity of epidermal growth factor receptor (EGFR) tyrosine kinase inhibitors was limited to the first-line setting and treatment discontinuation rates were higher than with mTOR inhibitors and SERDs. Overall, PFS benefit appears to be greatest when agents acting on CDK4/6, mTOR and Pi3K pathways, and SERDs are added to standard endocrine therapy. If these early results persist in further studies, these data are likely to change the way we treat hormone receptor positive, HER2 negative metastatic breast cancer. In the follow-up article to this review, we will consider the potential future treatment options for these patients.

Hormone receptor positive, HER2 negative metastatic breast cancer: Future treatment landscape.

Endocrine therapy is an established and effective treatment strategy for hormone receptor positive metastatic breast cancer. The clinical utility of endocrine therapy is lost over time due to evolving changes in tumor biology and the development of endocrine resistance. Many agents targeting the intracellular signaling pathways associated with endocrine resistance are in development. Encouraging early results have been seen for agents which directly target the estrogen receptor (ER), inhibitors of co-signaling pathways, inhibitors of ER chaperones, ER antagonists able to inhibit mutated or otherwise activated ERs, and modulators of histone acetylation restoring synthesis of ER signaling components. Following our systematic review of treatments with established benefits in this supplement, we review some of the more promising new strategies for overcoming endocrine resistance, looking at the impact on disease control and quality of life for women with hormone receptor positive, HER2 negative breast cancer. We also examine the biomarkers that may guide selection of the best therapy for the individual.