Cancer commonly arises at the sites of chronic inflam-mation and infection.Although this association has longbeen recognized,the reason has remained unclear.With-in the gastrointestinal tract,there are many examplesof inflammatory conditions associated with cancer,andthese include reflux disease and Barrett’s adenocarcino-ma of the esophagus,Helicobacter infection and gastriccancer,inflammatory bowel disease and colorectal cancerand viral hepatitis leading to hepatocellular carcinoma.There are several mechanisms by which chronic inflam-mation has been postulated to lead to cancer whichincludes enhanced proliferation in an endless attempt toheal damage,the presence of a persistent inflammatoryenvironment creating a pro-carcinogenic environmentand more recently a role for engraftment of circulatingmarrow-derived stem cells which may contribute to thestromal components of the tumor as well as the tumormass itself.Here we review the recent advances in ourunderstanding of the contributions of circulating bonemarrow-derived stem cells to the formation of tumors inanimal models as well as in human beings. Cancer commonly arises at the sites of chronic inflam- mation and infection. Although this association has longbeen recognized, the reason has been unclear. With-in the gastrointestinal tract, there are many examples of inflammatory conditions associated with cancer, and the of which include reflux disease and Barrett’s adenocarcino-ma of the esophagus, Helicobacter infection and gastriccancer, inflammatory bowel disease and colorectal cancerand viral hepatitis leading to hepatocellular carcinoma.There are several mechanisms by which chronic inflam-mation has been postulated to lead to cancer whichincludes enhanced proliferation in an endless attempt toheal damage, the presence of a persistent inflammatory environment creating a pro-carcinogenic environment and more recently a role for engraftment of circulatingmarrow-derived stem cells which may contribute to the stromal components of the tumor as well as the tumormass itself. Here we review the recent advances in our understanding of the contributions of circulating bonemarrow-derived stem cells to the formation of tumors inanimal models as well as in human beings.