POU1F1 and functioning gonadotropic adenoma: Based on IHC for pituitary transcription factor-1, steroidogenic factor-1, estrogen receptor α1, LH, FSH, ACTH, GH, PRL, and TSH, 48 of these tumors (43.6%) were categorized as null-cell adenomas, 54 (49%) as gonadotroph adenomas, and 8 (7.2%) as silent adenomas (4 stained for ACTH, 2 for PRL, and 1 each for GH and TSH).