The Evolution of Targeted Therapies in Early Hormone Receptor-Positive, HER2-Negative Breast Cancer

Breast cancer is the second most common malignancy worldwide, and over 70% of new diagnosis are of the hormone receptor-positive (HR+) and HER2-negative (HER2−) subtype. The cornerstone in management of early stage HR+ breast cancer has historically consisted of chemotherapy and endocrine therapies. Genomic assays in early stage HR+HER2− breast cancer has provided a prognostic tool for recurrence and a predictive tool to select patients for adjuvant chemotherapy. The introduction of bone-modifying agents and adjuvant CDK 4/6 inhibitors into early stage disease represents new therapeutic modalities aimed at reducing risk in high-risk HR+HER2− cancers. This manuscript aims to provide a comprehensive overview of the evidence behind endocrine therapy and recommended duration of treatment, genomic assays to guide chemotherapy delivery, data guiding use of bisphosphonate therapy to reduce bone recurrence, and indications for incorporating CDK 4/6 inhibitors. In addition, novel endocrine agents and targeted therapies under investigation are highlighted.