STAT3 serine phosphorylation in human GH pituitary tumors.

(a) Immunohistochemistry for phospho-serine (pS727-STAT3) in the normal adenohypophysis reveals reactivity in vascular endothelium providing an internal positive control; there is focal faint staining in scattered adenohypophysial cells and stroma is largely negative. (b) All but one of 8 somatotroph (GH) adenomas exhibited strong positivity whereas (c) all lactotroph (PRL) adenomas (n = 4) were negative or showed focal weak positivity. (d) Ten of 13 non-functional adenomas (6 gonadotrophs, 7 null cell) were also either negative or weakly positive.