WHO classification of soft tissue tumours: an update based on the 2013 (4th) edition

The fourth edition of the World Health Organization (WHO) Classification of Tumours of Soft Tissue and Bone was published in February 2013, and serves to provide an updated classification scheme and reproducible diagnostic criteria for pathologists. Given the relative rarity of soft tissue tumours and the rapid rate of immunohistochemical and genetic/molecular developments (not infrequently facilitating recognition of new tumour entities), this updated text edited by a consensus group is important for both practising pathologists and oncologists. The 2013 WHO classification includes several changes in soft tissue tumour classification, including several new entities (e.g., pseudomyogenic haemangioendothelioma, haemosiderotic fibrolipomatous tumour, and acral fibromyxoma), three newly included sections for gastrointestinal stromal tumours, nerve sheath tumours, and undifferentiated/unclassified soft tissue tumours, respectively, various 'reclassified' tumours, and a plethora of new genetic and molecular data for established tumour types that facilitate better definition and are useful as diagnostic tools. This article briefly outlines these updates based on the 2013 WHO classification of soft tissue tumours.