The Evolving Complexity of Treating Hormone Receptor-Positive, Human Epidermal Growth Factor Receptor-2 (HER2)-Negative Breast Cancer: Special Considerations in Older Breast Cancer Patients-Part II: Metastatic Disease.

Breast cancer is a disease of aging, and the incidence of breast cancer is projected to increase dramatically as the global population ages. The majority of breast cancers that occur in older adults are hormone-receptor positive, human epidermal growth factor receptor-2 (HER2)-negative phenotypes, with favorable tumor biology; yet, because of underrepresentation in clinical trials, less evidence is available to guide the complex care for this population. Providing care for older patients with metastatic breast cancer, with coexisting medical conditions, increased risk of treatment toxicity, and frailty, remains a clinical challenge in oncology. In this review, we provide an overview of the current evidence from clinical trials and subanalyses of older adults with hormone receptor-positive, HER2-negative metastatic breast cancer, highlighting data on the safety and efficacy of oral therapies, including endocrine therapy alone or in combination with cyclin-dependent kinase (CDK) 4/6 inhibitors, phosphatidylinositol 3-kinase (PI3K) inhibitors, and mammalian target of rapamycin (mTOR) inhibitors. In addition, we note the significant underrepresentation of older and frail adults in these studies. Current and future directions in research for this special population, in order to address significant knowledge gaps, include the need to improve long-term adherence to hormonal and targeted therapy, prospective clinical trials that capture clinical and biological aging endpoints, and the need for a multidisciplinary approach with integration of geriatric and oncology principles.