Fig. 2
From: STAT Signaling in the Pathogenesis and Treatment of Cancer
Mechanisms for STAT activation in cancer. A variety of pathways have been described leading to STAT activation in tumor cells, including (1) autocrine or (2) paracrine activation of cytokine receptors, (3) oncoprotein kinases for which STATs are not physiological substrates (such as Bcr-Abl), (4) mutated cellular tyrosine kinases (such as Src), (5) chimeric oncoproteins which activate kinases that normally phosphorylate STATs (such as Tel-Jak), (6) proteins that can activate a receptor independent of ligand (such as in HTLV-I transformation), and (7) activated serine kinases that do not activate the STATs per se, but may contribute to inappropriate responses to physiologic signals.