Figure 1. MSCs in tumor pathogenesis. Initial systemic factors released by tumor cells or by the disrupted surrounding tissues cause MSC mobilization and recruitment into tumors; MSCs cross vessel walls and home into cancers. MSC-derived trophic factors, including growth factors, chemokines and cytokines influence cancer cell phenotypes. The crosstalk between MSCs and cancer cells fosters remodeling of the tumor microenvironment and impacts other stromal cell types, including immune cells, enhances angiogenesis and/or permeabilization of the vasculature, causes cancer cell growth, local invasion and metastasis. Systemic factors derived from these interactions may influence distal sites/tissues, including secondary colonization sites.