OC08 - Transcription factor profiling in pituitary adenomas: WHO 2017 versus WHO 2022 classifications in 115 cases – a single-center experience

Background Transcription factor-based classification of pituitary adenomas has refined diagnostic precision, with WHO 2022, emphasizing immunohistochemical transcription factors (Pit-1, SF-1, Tpit) for lineage determination. Purpose This study compares WHO 2017 and 2022 classifications in 115 pituitary adenoma cases, evaluating their clinical correlations and diagnostic reclassification impact. Methods A retrospective analysis was conducted on 115 pituitary adenomas, collecting clinical data, hormone profiles (GH, PRL, ACTH, TSH, FSH, LH), Ki-67 index, and immunohistochemical expression of Pit-1, SF-1, and Tpit. Cases were reclassified according to WHO 2022 transcription factor-based criteria and compared with prior WHO 2017 hormone-based classification, analyzing shifts in subtype categorization and potential clinical implications. Results Using WHO 2022, transcription factor IHC enabled precise lineage assignment in previously “null cell” or ambiguously classified adenomas. Pit-1 positivity was found in lactotroph and somatotrophadenomas, while SF-1 and Tpit identified gonadotroph and corticotroph lineages, respectively. Notably, several NFPA cases under WHO 2017 were reclassified under specific lineages in WHO 2022, reducing the proportion of null cell adenomas. The Ki-67 index remained <3% in most cases, aligning with their low proliferation index, but a subset showed elevated indices requiring close clinical monitoring. Clinically, reclassification provided improved prognostic stratification and therapeutic guidance, especially in cases with silent corticotroph or plurihormonal differentiation. Conclusion Transcription factor-based classification per WHO 2022 improves diagnostic accuracy and reduces the proportion of unclassified pituitary adenomas, enabling better alignment with clinical management strategies. Routine application of Pit-1, SF-1, and Tpit immunostaining in pituitary adenomas is recommended to refine classification and guide prognostic assessment.