Recruitment of stem cells and partially differentiated progenitor cells is a process which accompanies and facilitates the progression of cancer.One of the factors complicating the clinical course of cancer is obesity,a progressively widespread medical condition resulting from overgrowth of white adipose tissue(WAT),com-monly known as white fat.The mechanisms by which obesity in uences cancer risk and progression are not completely understood.Cells of WAT secret soluble molecules(adipokines) that could stimulate tumor growth,although there is no consensus on which cell populations and which adipokines are important.Recent reports suggest that WAT-derived mesenchymal stem(stromal) cells,termed adipose stem cells(ASC),may represent a cell population linking obesity and cancer.Studies in animal models demonstrate that adipokines secreted by ASC can promote tumor growth by assisting in formation of new blood vessels,a process necessary for expansion of tumor mass.Importantly,migration of ASC from WAT to tumors has been demonstrated,indicating that the tumor microenvironment in cancer may be modulated by ASC-derived trophic factors in a paracrine rather than in an endocrine manner.Here,we review possible positive and adverse implications of progenitor cell recruitment into the diseased sites with a particular emphasis on the role in cancer progression of progenitors that are expanded in obesity.