IL6 and neoplasm: This review synthesizes evidence for bidirectional stromal-tumor cross-talk in which cytokine networks (e.g., transforming growth factor-beta, interleukin-6, and C-X-C motif chemokine ligand 12/C-X-C chemokine receptor 4) coordinate epithelial-mesenchymal transition, stemness, chemotaxis, and vascular remodeling.