====== Pituitary-specific positive transcription factor 1 ======

[[PIT1]] is a pituitary-specific transcription factor responsible for pituitary development and hormone expression in mammals and is a member of the POU family of transcription factors that regulate mammalian development. The POU family is so named because the first 3 members identified were PIT1 and OCT1 (MIM 164175) of mammals, and Unc-86 of C. elegans (Herr et al., 1988). PIT1 contains 2 protein domains, termed POU-specific and POU-homeo, which are both necessary for high affinity DNA binding on genes encoding growth hormone (GH; MIM 139250) and prolactin (PRL; MIM 176760). PIT1 is also important for regulation of the genes encoding prolactin and thyroid-stimulating hormone beta subunit (TSHB; MIM 188540) by thyrotropin-releasing hormone (TRH; MIM 257120) and cyclic AMP.[supplied by OMIM]
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[[The 2022 World Health Organization classification of tumors of the pituitary gland]] provides detailed histological subtyping of a [[PitNET]] based on the tumor [[cell lineage]], [[cell type]], and related characteristics. The routine use of [[immunohistochemistry]] for [[pituitary transcription factor]]s ([[PIT1]], [[TPIT]], [[SF1]], [[GATA3]], and [[ERα]]) is endorsed in this classification. The major PIT1, TPIT, and [[SF1]] lineage-defined PitNET types and subtypes feature distinct morphologic, molecular, and clinical differences. The "[[null cell]]" tumor, which is a diagnosis of [[exclusion]], is reserved for PitNETs with no evidence of adenohypophyseal lineage differentiation. Unlike the [[2017]] WHO classification, [[mammosomatotroph stem cell tumor]]s and [[acidophil stem cell tumor]]s represent distinct [[PIT1]]-lineage PitNETs. The diagnostic category of [[PIT1-positive plurihormonal tumor]] that was introduced in 2017 WHO classification is replaced by two clinicopathologically distinct PitNETs: the [[immature PIT1-lineage tumor]] (formerly known as silent subtype 3 tumors) and the [[mature plurihormonal PIT1-lineage tumor]].
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[[Plurihormonal PIT-1–Positive pituitary neuroendocrine tumor]]