Cancer is still a serious health problem that requires continuous monitoring. New approaches for tracking therapy response and predicting clinical results have been sparked by the shortcomings of conventional tissue biopsies. One such approach is the utilization of liquid biopsies, which offer a non-invasive means to monitor treatment response compared to traditional tissue biopsies. Liquid biopsies can be a powerful tool for personalized medicine due to their non-invasive nature and their ability to detect dynamic alterations within the tumor microenvironment. They represent an important research topic that continues to develop because as have the potential to profoundly improve cancer care by improving patient outcomes, detecting cancer early, and generating more effective treatment strategies. (Aharonov et al., 2023). Circulating extracellular vesicles (EVs) have been introduced as a promising liquid biopsy form. EVs carry a variety of genetic materials, proteins, lipids, and other essential components and are released by all cells, including cancer cells. Researchers and physicians can retrieve important insights into the biology of tumors, track the treatment efficiency, and estimate treatment outcomes by evaluating these molecular fingerprints found in EVs (Cho, 2021).

We start by outlining the ideal features of a cancer biomarker, discussing the numerous kinds of biomarkers and the methods currently employed to evaluate treatment response. Then, we introduce the various liquid biopsies, focusing on circulating EVs as a promising liquid biopsy form and discussing their biogenesis and various categories. We additionally describe the cargo that EVs carry, including proteins, lipids, and nucleic acids, with an emphasis on their potential role in cell communication and tumor development. Moving on to clinical applications, the chapter highlights how the content of EVs reflects the state of the tumor and its microenvironment, making them valuable diagnostic, prognostic, and predictive biomarkers for monitoring treatment response across different cancer types. Then, we are addressing the intriguing possibility of using EV analysis to identify molecular signatures associated with emerging drug resistance. While the potential of EV biomarkers in cancer therapy monitoring is promising, the chapter acknowledges the limitations, challenges, and future directions in EV biomarker research. The technical challenges of EV separation and analysis are discussed, with an emphasis on the need for standardized isolation procedures and data processing. Overall, this chapter contributes to understanding the evolving field of liquid biopsies and their potential to revolutionize precision oncology.