The World Health Organization reports that in 2008 there were more than 1.4 billion obese adults in the world and that cancer claimed the lives of 7.6 million that year. Whereas a number of previous studies have demonstrated a link between obesity and certain cancer, the physiological causes have not been identified.  Mikhail Kolonin, from, The University of Texas Health Science Center at Houston (Texas, USA), and colleagues completed a study in which adipose stromal cells were transplanted into mice; they observed these cells to become recruited by tumors, where they incorporate into blood vessels and become fat cells.   The researchers also observed that cancer induces a six-fold increase of adipose stromal cell frequency in the systemic circulation – where they are incorporated into blood vessels as pericytes and they can differentiate into adipocytes in an obesity-dependent manner.  The study authors conclude that: “our results suggest that [adipose stromal cells] recruited from endogenous adipose tissue can be recruited by tumors to potentiate the supportive properties of the tumor microenvironment."