Molecular mechanism regulating the multiple steps of endothelial progenitor cell biology during postnatal vasculogenesis. Recruitment and incorporation of EPCs into angiogenic sites requires a coordinated multistep process including mobilization, chemoattraction, adhesion, endothelial transmigration, migration, tissue invasion, in situ differentiation and paracrine and/or juxtacrine factor production. The major molecular mechanisms that have been implicated in the distinct steps of EPC biology are indicated. Figure adapted from Fusenig N, Marmé D (eds): Tumor Angiogenesis: Basic Mechanisms and Cancer Therapy. Springer; 2008. Chapter 17 with modifications .