Tumor microenvironment has emerged as an important target for cancer therapy. In particular, cancer-associated fibroblasts (CAF) seem to regulate many aspects of tumorigenesis. CAFs secrete a variety of soluble factors that act in a paracrine manner and thus affect not only cancer cells, but also other cell types present in the tumor stroma. Acting on cancer cells, CAFs promote tumor growth and invasion. They also enhance angiogenesis by secreting factors that activate endothelial cells and pericytes. Tumor immunity is mediated via cytokines secreted by immune cells and CAFs. Both immune cells and CAFs can exert tumor-suppressing and -promoting effects. CAFs, and the factors they produce, are attractive targets for cancer therapy, and they have proven to be useful as prognostic markers. In this review we focus mainly on carcinomas and discuss the recent findings regarding the role of activated fibroblasts in driving tumor progression.
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