Reciprocal interactions of tumor cells with the extracellular matrix (ECM), tumor-associated macrophages (TAM), carcinoma-associated fibroblasts (CAF), mesenchymal stem cells (MSC), and endothelial cells (EC). These interactions are mediated by direct cell-to-cell contact and/or the release of cytokines, chemokines, growth factors, matrix metalloproteases (MMPs), and ECM proteins. Eventually this results in epithelial-mesenchymal transition (EMT) of tumor cells, their migration, invasion, and dissemination to distant organs and the formation of metastases. For reasons of clarity, other stromal cell populations, e.g. lymphocytes and known interactions among different stroma cell populations are not shown.