Opposing roles of the immune system in tumors

The immune system can both promote and constrain cancer development. Chronic inflammatory conditions predispose to cancer formation in multiple organs, highlighting the role of the immune system in promoting tumorigenesis (1). Conversely, the immune system can target and kill neoplastic cells, owing to their molecular differences from normal cells (2). Therefore, tumor development is aided by processes intrinsic to cancer cells that either exploit protumorigenic inflammation or evade antitumor immune responses. On pages 1326 and 1327 of this issue, Del Poggetto et al. (3) and Martin et al. (4), respectively, demonstrate how cancer cells may co-opt these opposing effects of the immune system during tumor development. Together, these studies highlight how the immune system influences the genetic and epigenetic alterations in cancer cells, which may lead to improved strategies for cancer prevention and therapy.