Exosomes are small extracellular vesicles, with a size of 100 nm or less, composed of lipid bilayers. These vesicles are released by cells and contain proteins, nucleic acids, and lipids that are specific to their parent cells. Circulating throughout the body, exosomes serve as messengers, transferring the molecular cargo from the original cells to recipient cells. In the context of cancer, exosomes derived from cancer cells can play a significant role in tumor development, invasion, metastasis, and drug resistance by facilitating intercellular communication within the tumor microenvironment. By detecting cancer-specific proteins and nucleic acids present in these exosomes, it becomes possible to diagnose cancer at an early stage and predict its prognosis. Notably, recent studies have explored the potential of disease cell-derived exosomes as diagnostic markers for various cancers, including lung, breast, and pancreatic cancers, as well as neurodegenerative diseases, such as Alzheimer’s and Parkinson’s. This chapter provides an overview of the current advancements in detecting cancer-derived exosomes as diagnostic biomarkers for cancer and discusses future research directions in this field.