EGFR and glioblastoma: In glioblastoma, a constitutively active mutant of epidermal growth factor receptor was found, and this mutant contributes to and sustains STAT3 activation by inducing a cytokine circuit involving IL-6 and leukemia inhibitory factor, which in turn activates gp130 in the neighboring cells that harbor wild-type epidermal growth factor receptor, leading to an enhanced growth of the entire tumor [75].