MMP9 and pituitary gland adenoma: Based on the fact that TNF-α and TNFR1 are present in normal and tumoral anterior pituitary cells [26,27], we hypothesized that TNF-α may enhance MMP-9 and VEGF expression, which, in turn, contributes to hemorrhagic transformation in pituitary adenomas via degrading components of vascular basement lamina and increasing vascular permeability.