ED-1 PITUITARY TUMORS IN 5TH WHO CLASSIFICATION 2022: WHAT DO YOU MEAN BY PITNET?

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Abstract It has been well known that the terminology has been changed from pituitary adenoma(4th WHO) which means benign epithelial tumors to pituitary neuroendocrine tumor(5th WHO 2022). It is apparent that the anterior pituitary cells and derived tumors contain intracytoplasmic neurosecretory granules and belong to neuroendocrine cells, and naturally neuroendocrine tumors. The pancreatic and gastrointestinal neuroendocrine neoplasms(NEN) are composed of well differentiated neuroendocrine tumors(NET) and poorly differentiated neuroendocrine carcinoma(NEC). NETs are potentially malignant(metastatic) tumors and are further graded to G1,G2,G3 by proliferative activities(mitoses or Ki-67 indices) showing correlation with prognosis . PitNET which means pituitary NET is now classified by transcription factors(PIT1,TPIT,SF1) and some tumors show clinical symptoms,(hormone production) invasive growth and rarely metastasize indicating potential malignant behavior. From this broad biological spectrum of PitNET, ICD-O coding /3(primary malignancy) has been proposed(5th WHO CNS, Pediatrics and Endocrine volumes). It has been known that some histological patterns (Sparsely granulated somatotroph PitNET, Crooke cell PitNET and others) are related more aggressive growth of PitNETs, but metastatic behavior is very hard to predict histologically. So in WHO 4th edition, the term pituitary carcinoma was used only after confirming metastasis or remote spread. The metastatic tumors are now called metastatic PitNETs. Five tiered grading by proliferation and invasion has been also proposed(Trouillas). Now we need more updated genomic studies such as single cell RNA sequencing to clarify biologic behavior of the individual PitNET cells to further clarify the their nature. . In my talk, several points of interests regarding PitNETs will be discussed by demonstrating histology and biology of representative cases.

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