The use of liquid biopsy in early breast cancer: clinical evidence and future perspectives

Liquid biopsy, including both circulating tumor cells and circulating tumor DNA, is gaining momentum as a diagnostic modality adopted in the clinical management of breast cancer. Prospective studies testing several technologies demonstrated clinical validity and, in some cases, achieved the United States Food and Drug Administration approval. The initial testing and clinical application of liquid biopsy focused primarily on the diagnosis, while molecular characterization and monitoring of metastatic disease, with larger data from prospective studies, came in the last two decades. Although its role in metastatic setting is thus widely recognized, the current evidence does not provide support for the routine clinical use of liquid biopsy methods for the earlier stage of this disease. Considering the relevance of early detection, characterization, and management of breast cancer in the early-stage, this clinical setting is the most suitable to increase the chances for effective treatment selection and improved prognosis, and a better understanding of the main application of liquid biopsy tools in the earlier stage of breast cancer is therefore crucial. The aim of this review is to provide an overview of the clinical evidence and subsequent potential applications of liquid biopsy in early breast cancer, identifying the main existing caveats and the possible future scenarios.