Current Status and Future Perspectives of Antibody–Drug Conjugates in Hormone Receptor-Positive Breast Cancer

Breast cancer is the most common cancer type in women. The vast majority of breast cancer patients have hormone receptor-positive (HR+) tumors. In advanced HR+ breast cancer, the combination of endocrine therapy with cyclin-dependent kinase 4/6 (CDK4/6) inhibitors is considered the standard of care in the front-line setting. Nevertheless, resistance to hormonal therapy and CDK4/6 inhibitors eventually occurs, leading to progression of the disease. Antibody–drug conjugates (ADCs) comprise a promising therapeutic choice with significant efficacy in patients with HR+ breast cancer, which is resistant to endocrine treatment. ADCs typically consist of a cytotoxic payload attached by a linker to a monoclonal antibody that targets a specific tumor-associated antigen, offering the advantage of a more selective delivery of chemotherapy to cancer cells. In this review, we focus on the ADC mechanisms of action, their toxicity profile and therapeutic uses as well as on related biomarkers and future perspectives in advanced HR+ breast cancer.