Adjuvant cyclin-dependent kinase 4/6 inhibition in hormone receptor-positive breast cancer: One Monarch to rule them all?

The use of cyclin-dependent kinase 4/6 (CDK4/6) inhibitors has dramatically improved outcomes for patients with metastatic, hormone receptor (HR)-positive breast cancer. Because of the continued high rate of relapse in patients with node-positive, HR-positive disease, evaluating these agents in the adjuvant setting is the logical next step. Three adjuvant CDK inhibitor trials have been reported to date, with only 1 of them showing a statistical advantage for the CDK inhibitor in comparison with endocrine therapy alone. These trials have key similarities and differences that could explain the disparate results. The one positive trial has a relatively short follow-up, and continued analysis is critical to confirm the benefit of adjuvant CDK inhibition in this setting. It is imperative that predictive biomarkers be determined so that these agents can be used in the patients most likely to benefit and thus the additional toxicity and expense can be avoided in those who do not require these agents. LAY SUMMARY: There is a critical need for new agents to prevent relapse in patients with hormone receptor-positive breast cancer. Trials to date evaluating cyclin-dependent kinase inhibitors, which decrease how quickly cancer cells multiply, have shown mixed results, with only 1 trial demonstrating that these agents decrease recurrence.

The Changing Landscape of Breast Cancer: How Biology Drives Therapy

Breast cancer is the most prevalent life-threatening cancer in women. Optimizing therapy to increase cure rates in early stage disease, and improving life expectancy and palliation for advanced stages, are goals driving major areas of research. The armamentarium of targeted treatments for breast cancer is ever expanding as understanding of breast cancer biology deepens. A revolution in our treatment was heralded a decade ago by the introduction of trastuzumab for human epidermal receptor-2 positive (HER2+) disease resulting in remarkable reductions in recurrence and improvements in overall survival (OS). Advances continue to be made in other breast cancer subtypes targeting key activating pathways for therapeutic development. However, for these other targeted agents, improvement in OS has been elusive. This article focuses on the development of targeted therapy in breast cancer focusing primarily on the last 5 years, to illustrate that as we understand the complex pathways allowing the dysregulated cell to become malignant, it also propels us closer towards the promise of precision and personalized medicine.