Liquid Biopsy in Metastatic Breast Cancer: Path to Personalized Medicine

Background: The detection of circulating tumor cells (CTCs) and circulating tumor DNA (ctDNA) in breast cancer has seen significant progress over the last two decades. These blood-based biomarkers offer a minimally invasive alternative to traditional methods for assessing disease progression and monitoring treatment response, with the potential to transform breast cancer management. Summary: CTCs and ctDNA have emerged as valuable tools for prognosis and treatment guidance in breast cancer. Studies have shown that CTC count correlates with survival and changes in CTC levels can predict clinical outcomes (STIC CTC, DETECT III). Additionally, the molecular characterization of CTCs can help guide therapy (DETECT III). ctDNA, while also predictive of survival (BioItaLEE), provides further utility in identifying treatment failure (PADA-1, PALOMA III) and functions as a real-time tumor biopsy (plasmaMATCH, MONALEESA). Despite these promising advances, challenges remain, including the rarity of CTCs and the need for standardization in ctDNA detection methods. Key Messages: CTC and ctDNA detection has improved significantly and holds the potential for less invasive breast cancer management. CTCs are associated with survival outcomes and treatment guidance, while ctDNA is helpful in predicting treatment failure and can serve as a dynamic tumor biopsy. Ongoing research is needed to address the challenges of CTC rarity and variability in ctDNA detection methods for widespread clinical use.