Endocrine and Neuroendocrine Tumors: Updates From the 5th Edition of the World Health Organization “Blue Book”

The 5th edition refines the understanding of neuroendocrine cell relationships in various organs, incorporating the proposed International Agency for Research on Cancer/WHO classification for neuroendocrine neoplasms from 2018. This includes a more detailed cytogenesis-based classification of pituitary neuroendocrine tumors. Key revisions include the reclassification of thyroid neoplasms, based on cytogenesis and pathogenesis, particularly for follicular cell-derived tumors. The text introduces new terminology for benign endocrine proliferations, emphasizing the distinction between hyperplasia and neoplasia. Changes include the reclassification of multifocal, multiglandular parathyroid disease in primary hyperparathyroidism as multiple adenomas in genetic tumor syndromes. The terminologies thyroid follicular nodular disease and adrenocortical nodular disease are introduced. This edition underscores the critical role of accurate immunohistochemistry in endocrine pathology. Standards for quantifying cellular proliferations, including assessing mitotic activity and Ki-67 labeling indices, are discussed across various tumor types. The classification concludes with a chapter on genetic tumor syndromes associated with endocrine tumors. This edition advances our knowledge in endocrine tumors, incorporating cutting-edge molecular information and addressing essential technical considerations in diagnosis and classification.