A digest on the role of the tumor microenvironment in gastrointestinal cancers.

Experimental studies and analyses of clinical material have convincingly demonstrated that tumor formation and progression occurs through a concerted action of malignant cells and the surrounding microenvironment of the tumor stroma. The tumor microenvironment is comprised of various cell types like fibroblasts, immune cells, vascular cells and bone-marrow-derived cells embedded in the extracellular matrix. This review, focusing on recent findings in the context of gastrointestinal tumors, introduces the different stromal cell types and delineates their contributions to cancer initiation, growth and metastasis. By selected examples we also present how the tumor microenvironment is emerging as a promising target for therapeutic intervention.