Immunohistochemistry (IHC) of cell lineage-specific transcription factors (TFs) has been added to the histopathological classification of pituitary adenomas since 2017, resulting in new histopathological subtypes of TF+/hormone−non-functioning pituitary adenomas (NFPAs) and a reduction in the prevalence of null cell adenomas (NCAs). This evidence concerns the gene TF and pituitary gland adenoma.