Reactive oxygen species: a volatile driver of field cancerization and metastasis.

Field cancerization and metastasis are the leading causes for cancer recurrence and mortality in cancer patients. The formation of primary, secondary tumors or metastasis is greatly influenced by multifaceted tumor-stroma interactions, in which stromal components of the tumor microenvironment (TME) can affect the behavior of the cancer cells. Many studies have identified cytokines and growth factors as cell signaling molecules that aid cell to cell communication. However, the functional contribution of reactive oxygen species (ROS), a family of volatile chemicals, as communication molecules are less understood. Cancer cells and various tumor-associated stromal cells produce and secrete a copious amount of ROS into the TME. Intracellular ROS modulate cell signaling cascades that aid in the acquisition of several hallmarks of cancers. Extracellular ROS help to propagate, amplify, and effectively create a mutagenic and oncogenic field which facilitate the formation of multifoci tumors and act as a springboard for metastatic tumor cells. In this review, we summarize our current knowledge of ROS as atypical paracrine signaling molecules for field cancerization and metastasis. Field cancerization and metastasis are often discussed separately; we offer a model that placed these events with ROS as the focal instigating agent in a broader "seed-soil" hypothesis.