Cancer cells exhibit abnormal behavior compared to normal cells. They ignore growth arrest signals such as contact inhibition, a mechanism that stops their proliferation when they collide with surrounding cells, and proliferate in an uncontrolled manner, destroying tissue. Early detection and treatment of cancer are therefore important for healthy longevity. Cancer cells differ from normal cells in their characteristic gene expression due to their abnormalities. Cancer markers that reflect these characteristics have been searched for and applied to diagnosis. Although analysis of blood antigens has been the main method, further development of a diagnostic system is needed for early detection of cancer. Next-generation sequencers have improved gene expression analysis technology, making it possible to analyze detailed gene expression in cancer cells and nucleic acid molecules in blood or urine. In addition, cancer cells release extracellular vesicles, exosomes, which are known to contain molecules that may serve as cancer markers. This review summarizes the latest findings on exosomal cancer markers.