Senescent stromal cells: roles in the tumor microenvironment

Cellular senescence forms a barrier to tumorigenesis, by inducing cell cycle arrest in damaged and mutated cells. However, once formed, senescent cells often emit paracrine signals that can either promote or suppress tumorigenesis. There is evidence that, in addition to cancer cells, subsets of tumor stromal cells, including fibroblasts, endothelial cells, and immune cells, undergo senescence. Such senescent stromal cells can influence cancer development and progression and represent potential targets for therapy. However, understanding of their characteristics and roles is limited and few studies have dissected their functions in vivo. Here, we discuss current knowledge and pertinent questions regarding the presence of senescent stromal cells in cancers, the triggers that elicit their formation, and their potential roles within the tumor microenvironment.