The 5th edition of the World Health Organization Classification of Tumours of the Eye and Orbit

The 5th edition of the World Health Organization (WHO) Classification of Tumours of the Eye and Orbit is the latest step in standardizing the diagnostic practice worldwide. Building upon the 4(th) edition, published in 2018, the 5(th) edition introduces new chapters on the eyelid and orbital tumors, and consolidates sections on hematolymphoid tumors, soft tissue and bone tumors, metastases and genetic tumor predisposition syndromes into dedicated chapters. Written in the format of the other 5(th) edition volumes, a systematic approach is taken to describe the defining characteristics of each tumor type and its staging, with the addition of macroscopic appearance, cytology, diagnostic molecular pathology, and essential and desirable diagnostic criteria. This volume highlights recent advances in the etiology, pathogenesis, and diagnosis of tumors of the eye and ocular adnexa. Radiologic and ophthalmic features are also emphasized. Moreover, the 5(th) edition includes updates on the classification scheme for certain tumors, such as vascular anomalies, and introduces tumors that have been recently identified in the eye and ocular adnexa. This editorial summarizes the major general changes in the 5(th) edition of the WHO classification of Tumours of the Eye and Orbit, and the specific updates in each taxonomic category, with an emphasis on advances in understanding tumor pathogenesis, diagnostic and prognostic criteria, and novel immunohistochemical and molecular markers.