Role of the microenvironment in tumourigenesis: focus on virus-induced tumors.

Tumor microenvironment can differ considerably in various types of tumors in terms of cellular and cytokine networks and molecular drivers. The well known link between inflammation and cancer has recently found a number of genetic and molecular confirmations. In this respect, numerous reports have revealed that infection and chronic inflammation can contribute to cancer development, progression and control. Adhesion molecules, chemokines and proinflammatory cytokines, that enroll leukocytes, are persistently present in cancer microenvironment, thus increasing the risk for developing tumors. In this respect, cancer-derived microvescicles, in particular exosomes, exert an important role in the recruitment and reprogramming of components of tumor microenvironment. The relationship between cancer and virus infection has generated, in recent years, a great interest for studies aiming to better understand the role of the immune system in the control of these infections and of the immune cofactors in the promotion of the virus-induced neoplastic transformation. This suggests that virus-induced immune alterations may play a role to create an immunotolerogenic microenvironment during the carcinogenesis process.