Mesenchymal stem cells which are the group of cells that can be isolated from various tissues having the ability of morphing into distinct tissue types and self-renewal have constituted the most popular topic for the stem cell research. Mesenchymal stem cells and cancer cells share common properties like high level of telomerase enzyme activity, deprogramming and proliferation, immortalization, self-renewal, and invasion. As a result of these, common properties have been suggested that some embryonic genes are reexpressing in cancer cells. Additionally, of these properties, MSCs have been shown to have a remarkable tropism towards tumors, so that stem cells might be the key factors of the cancer formation and propagation. There are some studies about the interactions between cancer and stem cells. As a result of these studies, MSCs, with their immunosuppressive activities, vasculogenic supports, anti-apoptotic properties, and being a component of tumor tissue, could affect cancer cells as a promoter, or they could affect tumor formation and propagation as an inhibitor.