Plasticity beyond cancer cells and the "immunosuppressive switch".

Tumor initiation, growth, and metastatic progression are complex processes that, in order to be successful, require extraordinary cellular plasticity. Accordingly, tumor cell plasticity and how it affects disease progression have been studied extensively. However, as our understanding of the tumor microenvironment deepens, we are confronted with the notion that functional plasticity in the context of cancer is not limited to tumor cells alone but is also commonly seen in normal stromal cells of the microenvironment, and specifically in immune cells. Here, we review the functional plasticity these cells exhibit in the context of cancer, highlighting the role of circulating and tumor-associated neutrophils. We further discuss how this plasticity supports or limits tumor progression, inducing an "immunosuppressive switch" to promote further tumor growth and development. ©2015 American Association for Cancer Research.