Update on pituitary adenomas in the 2017 World Health Organization classification: innovations and perspectives.

The World Health Organization (WHO) classifications of tumors offer invaluable support in the diagnosis of tumors, with every new edition including novel information and diagnostic updates. The new 2017 WHO Classification of Tumors of Endocrine Organs, 4th edition, includes innovations in both terminology and diagnostic guidelines for pituitary adenomas, along with new entities, molecular information, and novel treatment modalities. The recommended reporting system of pituitary adenomas is based on morphology and assessment of the hormonal content by immunohistochemistry. Electron microscopy and immunohistochemistry for Ki-67 and p53 and transcription factors, while presenting additional information, are not recommended for routine diagnosis. Other markers may also yield information of prognostic and predictive significance. In sum, the 2017 WHO classification provides pathologists and clinicians with new and comprehensive information of great use for the diagnosis and treatment of pituitary tumors.