Beyond Hormone Receptors: liquid biopsy tools to unveil new clinical meanings and empower therapeutic decision-making in Luminal-like metastatic breast cancer.

Immunohistochemical (IHC) tissue profiling is a standard practice in the management of metastatic breast cancer (mBC), that enables the identification of distinct biological phenotypes based on hormone receptors' expression. Luminal-like tumors primarily benefit from a first line treatment strategy combining endocrine therapy and cyclin-dependent kinase 4/6 inhibitors. However, IHC analyses necessitate invasive procedures and may encounter technical and interpretational challenges. In the current era of precision medicine, liquid biopsy holds potential to provide clinicians with additional insights into disease biology, including mechanisms underlying endocrine resistance and disease progression. Several liquid-based biomarkers are entering clinical practice and hold prognostic and predictive values in Luminal-like mBC, while many others are currently being investigated. The present work aims to summarize the current evidence regarding the clinical meanings of hormone receptors and their downstream molecular pathways, alongside their implications for therapeutic decision-making in Luminal-like mBC.