In the past several years, the importance of microRNA (miRNA) in cancer cells has been recognized. Dysregulation of miRNAs leads to the cancer development, meaning that expression profile of miRNAs can be used as cancer biomarker. Currently, it was discovered that extracellular RNAs (exRNAs) circulate in the blood of both healthy and diseased patients　and these exRNAs are packaged in extracellular vesicles such as exosomes, and are, therefore, highly stable. The existence of circulating miRNAs and exosomes in the blood of cancer patients has raised the possibility that disease-specific miRNAs and exosomes may serve as a novel diagnostic marker. Moreover, exosomes secreted from tumor cells contribute micromanaging tumor microenvironment, since exosomes carrying pathogenic components and are secreted from tumor cells. Here we will discuss importance of transfer of genetic materials by exosomes and their contribution to tumor development and metastasis. Furthermore, we will present our current progress on anti-cancer strategy by tumor-specific inhibition of EV-secretion.