Figure 1.
Tumor dormancy and matricellular proteins. Three types of tumor dormancy exist: cellular dormancy (A), angiogenic dormancy (B) and immunological dormancy (C). Cancer cells enter into G0–G1 arrest during cellular dormancy. Angiogenic dormancy is regarded as a state during which pro-angiogenic factors are balanced with anti-angiogenic factors, resulting in poor vascularization and limited tumor size. Immunological dormancy refers to a state during which the active immune system clears most of tumor cells, leading to an equilibrium between cell population and immunological clearance. (D) DTCs exit from tumor dormancy and turn into metastatic outgrowths. (E) TSP-1 is rich in mature vessel stalks and maintains disseminated breast cancer cells in a dormant state, whereas POSTN, tenascin-C and TGF-β1 are distributed at neovascular tips and enable DTCs to escape from the dormant state and undergo metastatic outgrowth. (F) OPN assists acute lymphoblastic leukemia cells in anchoring to the bone marrow endosteal niche and promotes dormancy