Liquid biopsy in breast cancer: clinical implications of ctDNA and CTCs in diagnosis, treatment and monitoring.

One of the leading causes of cancer-related death in women is breast cancer (BC). BC is a heterogeneous tumor. Although tissue biopsy is the gold standard for the diagnosis of BC, often tissue specimens are not informative enough about the tumor heterogeneity. The concept of "Liquid Biopsy" has recently emerged as a powerful clinical tool capable of better identifying mutations associated with the presence of primary or metastatic tumors. This article focuses on the clinical applications of circulating tumor cells (CTCs) and circulating tumor DNA (ctDNA) in breast cancer progression, relapse, diagnosis, and treatment response. The most important molecules analyzed in Liquid Biopsy are cfDNA, ctDNA, and CTCs. All these factors may be considered as non-invasive biomarkers for the early diagnosis of BC or to predict the progression and prognosis of patients, including BC recurrence and patients' treatment response. However, the clinical utility of ctDNA analysis and CTCs requires further investigation through better-designed studies to ensure their precision and diagnostic performance. In conclusion, liquid biopsy and ctDNA analysis demonstrate the potential to transform breast cancer management, with applications in screening, monitoring tumor progression, or response to treatment.