Exosomes offer a new perspective on the biology of cancer with both diagnostic and therapeutic concepts. Due to the cell-to-cell association, exosomes are involved in the progression, metastasis, and therapeutic efficacy of the tumor. They can be isolated from blood and other body fluids to determine the disease progression in the body, including cancer growth. In addition to being reservoirs of biochemical markers of cancer, exomes can be designed to restore tumor immunity. Tumor exosomes interact with different cells in the tumor microenvironment to confer beneficial modulations, responsible for stromal activity, angiogenesis, increased vascular permeability, and immune evasion. Exosomes also contribute to the metastasis with the aim of epithelial transmission to the mesenchyme and the formation of premetastatic niches. Moreover, exosomes protect cells against the cytotoxic effects of chemotherapeutic drugs and prevent the transmission of chemotherapy resistance to adjacent cells. Therefore, exosomes are essential for many fatal cancer agents, and understanding their origins and role in cancer is important. In this article, we attempted to clarify the potential of exosomes for the application in cancer diagnosis and therapy.