GLI1 and cancer: Thus it forms an auto-positive feedback loop that enhances Shh signaling outcomes.5, 18 Although Gli1 is not essential for development, it is a potent oncogene and is required for Shh-induced tumor growth.19, 20, 21 Gli1 expression is elevated in many cancer types with elevated Shh signaling.3 Inhibiting Gli1 activity would likely be an effective approach for treating these cancers.