Circulating tumour DNA as a promising biomarker for breast cancer diagnosis & treatment monitoring.

Breast cancer contributes a large fraction to mortality among women diagnosed with cancer. It is important to monitor residual disease and extend the lead time to detect relapse in high-risk patients. Minimally invasive techniques that utilise circulating biomarkers are being explored for their potential in diagnosis, prognosis, and disease monitoring of breast cancer. Circulating biomarkers have been investigated as tools for breast cancer diagnosis, prognosis, prediction, and monitoring of therapeutic response and resistance. Among these, circulating tumour cells and cell-free plasma DNA (cfDNA) derived from tumour cells (circulating tumour DNA i.e. ctDNA) have been integrated into clinical trial designs. Among all circulating biomarkers, ctDNA stands out as a promising biomaterial with great potential as it is thought to mirror the tumour's evolution. However, its clinical utilisation is hampered mainly by gaps in knowledge of its biological properties and specific characteristics. The development of robust and standardised methods for assessing circulating biomarkers is essential for realising the potential of personalised medicine. This review aims to summarise the characteristics of ctDNA and its role in breast cancer, drawing from both basic and translational research to provide insights into its clinical application. This review suggests that ctDNA has the potential to be a non-invasive, real-time surrogate for tumour tissue-based biomarkers. In conclusion, circulating biomarkers have the potential to revolutionise breast cancer diagnosis, prognosis, and treatment monitoring, but the development of standardised methods for their assessment is essential. ctDNA, in particular, shows great promise as a liquid biopsy tool, but further research is needed to understand its biology and ensure its clinical utility fully.