What do you mean by PitNETs in WHO Classification 2022?

This review is aimed at clarifying the background and the meaning of new terminology "pituitary neuroendocrine tumours" (PitNETs) in WHO Classification 2022. The PitNETs share the unique structures of secretory granules (SG) with other neuroendocrine tumors, the good example of which is the pancreatic NETs which are now considered to be potentially aggressive, i.e., invasive and metastatic. The PitNETs share these features of pancreatic NETs and now are considered to be potentially aggressive tumors. The PitNETs are classified according to the functions (hormones) and transcription factors, PIT1, TPIT and SF1. The PitNETs are usually slow growing tumors with generally low (<3%) Ki-67 indices. PitNETs show some morphologic features which are more closely related to aggressive growths, such as Crooke cells. The questions how those particular PitNETs are aggressive have been approached by molecular techniques such as single cell RNA seq to clarify the genomic heterogeneity and the biology of individual tumor cells. It is expected that the PitNETs will be clarified and classified with more biologically and therapeutically oriented manner.