Cancer invasion and the microenvironment: plasticity and reciprocity.

Cancer invasion is a cell- and tissue-driven process for which the physical, cellular, and molecular determinants adapt and react throughout the progression of the disease. Cancer invasion is initiated and maintained by signaling pathways that control cytoskeletal dynamics in tumor cells and the turnover of cell-matrix and cell-cell junctions, followed by cell migration into the adjacent tissue. Here, we describe the cell-matrix and cell-cell adhesion, protease, and cytokine systems that underlie tissue invasion by cancer cells. We explain how the reciprocal reprogramming of both the tumor cells and the surrounding tissue structures not only guides invasion, but also generates diverse modes of dissemination. The resulting "plasticity" contributes to the generation of diverse cancer invasion routes and programs, enhanced tumor heterogeneity, and ultimately sustained metastatic dissemination.