The 2026 World Health Organization Classification of Tumors of Soft Tissue and Bone: 6th Edition.

The 6th edition of the World Health Organization Classification of Soft Tissue and Bone Tumors (STB6) integrates the latest scientific and molecular discoveries with decades of pathological expertise to establish a globally accepted common language for diagnosis and clinical behavior. In this volume, the "essential" and "desirable" diagnostic criteria have been refined, considering different resource settings, ensuring accuracy while maintaining flexibility. A tumor type (entity) is a tumor in which multiple parameters (eg, clinical, histopathological, and/or genetic features) differ from those of other tumor types. In total, 19 new entities met these criteria and were added. A subtype is different in at least one dimension from the main tumor type (clinical, histopathological, or genetic), preferably resulting in a different treatment or outcome. A morphological pattern (no longer "variant") is important for pathologists to be aware of to facilitate recognition but is not associated with different clinical behavior. The classification was drafted by 203 editors and authors from 27 countries, representing genetics, medical oncology, surgical oncology, orthopedic surgery, and radiology, in addition to pathology. STB6 includes soft tissue tumors (n=116), bone tumors (n=46), vascular tumors of soft tissue and bone (n=18), undifferentiated spindle and round cell sarcomas (n=4), hematopoietic and dendritic cell neoplasms (n=6), and genetic syndromes (n=6). In total, 62 sarcomas are included. A consensus was reached among the expert editorial board. In this review, we highlight changes in tumor classification in STB6, including recently described tumor types, novel diagnostic markers, recent discoveries in molecular genetics, and improvements in prognostication.