Know thy neighbor: stromal cells can contribute oncogenic signals

Although the stroma within carcinogenic lesions is known to be supportive a nd responsive to tumors, new data increasingly show that the stroma also ha s a more active, oncogenic role in tumorigenesis. Stromal cells and their p roducts can transform adjacent tissues in the absence of pre-existing tumor cells by inciting phenotypic and genomic changes in the epithelial cells. The oncogenic action of distinctive stromal components has been demonstrate d through a variety of approaches, which provide clues about the cellular p athways involved.