2026 年 WHO 软组织与骨肿瘤分类（第 6 版）：新增 19 个实体与主要变化The 2026 World Health Organization Classification of Tumors of Soft Tissue and Bone: 6th Edition

Scope: open-access full text (CC BY-NC-ND 4.0) from the AJSP publisher page, including 9 figures, 3 tables (with notes) and acknowledgments; the reference list and the WCT Standing Editorial Board roster are not included. Superscript numbers are the original reference numbers.

The World Health Organization (WHO) classification of Tumors (WCT) provides a uniform nomenclature and standardized framework for categorizing tumors of soft tissue and bone, facilitating accurate diagnosis, guiding treatment, informing research, epidemiological reporting, and the development of international reporting and treatment guidelines. The 6th edition of the WHO Classification of soft tissue and bone tumors (STB6) is an update of the 5th edition classification, encompassing some major and minor changes. The 6th edition integrates the latest scientific and molecular discoveries with decades of pathological expertise to establish a globally accepted common language for soft tissue and bone tumor diagnosis and management. The criteria used for considering inclusion of new entities into this volume included publication of at least 5 cases of the neoplastic entity by 2 independent groups in peer-reviewed journals; any borderline entities included are referred to as “provisional” rather than “emerging.”

In this volume, the “essential and desirable diagnostic criteria” for tumors have been developed considering different resource settings, ensuring diagnostic accuracy while maintaining flexibility. The “essential criteria” are mostly morphology-based, including certain essential, invariably “basic” immunohistochemical (IHC) stains, except for molecularly defined tumors such as sarcomas with BCOR alterations, for which molecular confirmation is considered essential. The “desirable criteria” include an additional diagnostic layer of molecular tests and/or “newer” resources, including surrogate IHC markers. The morphology codes of the updated International Classification of Diseases Oncology, 4th iteration (ICDO-4) have been included for each tumor type and subtype in STB6, ensuring and facilitating more accurate and granular epidemiological data collection.¹ Inclusion of tumor types and subtypes is based on better definitions. A tumor type (entity) is a tumor in which multiple parameters (eg, clinical, anatomic, histopathological, and/or molecular features) differ from those of other tumor types. A subtype is recognized as being 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 called “variant”) is defined as a specific morphology of a given tumor type, important for pathologists to be aware of to facilitate recognition, but not associated with different clinical behavior.

The classification was drafted by 203 editors and authors from 27 countries, representing radiology, medical oncology, genetics, surgical oncology, and orthopedic surgery, in addition to pathology. When appropriate, responsible authors from the previous 5th edition were acknowledged for their contributions, providing the basis for the 6th edition. A consensus was subsequently reached among the expert editorial board. Entities with specific organ-restricted presentation, such as biphenotypic sinonasal sarcoma or uterine sarcomas, are excluded from STB6 and instead discussed in other WCT volumes, with the exception of gastrointestinal stromal tumors, as in many centers, these are treated by sarcoma surgeons and medical oncologists and are discussed in sarcoma multidisciplinary teams.

CHANGES IN HISTONE GENE ANNOTATIONS

With regard to the annotation of histone H3 protein nomenclature, a hybrid format is used as a practical compromise that preserves the widely recognized legacy terminology (which uses protein numbering excluding the initiating methionine that is cleaved from the mature protein) while remaining aligned with genetic reporting standards;² specifically, the 3-letter amino acid description is omitted and the legacy terminology is given in parentheses, for example, H3.3 p.G35W (G34W) in giant cell tumor of bone. For IHC markers targeting histone proteins, we retain the established epitope-based terminology (eg, H3K36M and H3K27me3) without the “p.” prefix and with the conventionally used formatting (eg, H3K27me3 without spaces). These terms refer to protein expression or posttranslational modifications rather than genomic alterations and are therefore most consistent with current diagnostic practice and the published literature.

CHANGES IN THE CLASSIFICATION FRAMEWORK OF STB6

In the 5th edition, separate sections on vascular tumors were included in both the soft tissue and bone tumor chapters, which was mainly driven by their different clinical behavior. Vascular tumors in bone often present as multifocal disease, and epithelioid hemangioma is locally aggressive in bone, while benign in soft tissue. In this edition, these sections were combined to limit redundancy; differences between bone and soft tissue presentation are clearly marked within the respective sections.

STB6 has also taken a different approach to hematolymphoid tumors of the soft tissues and bone, combining them into one chapter. Tumors included in this chapter are hematopoietic neoplasms typically derived from lymphoid, plasma cell, or histiocytic/dendritic cell lineages that arise in nonmucosal extranodal soft tissues or involve bone primarily, often presenting as mass-forming and/or destructive osseous lesions.

In other WHO 6th edition books (released and upcoming), various soft tissue tumor entities are presented in a harmonized way, mostly within a combined chapter of “mesenchymal tumors.”

SOFT TISSUE TUMORS

Significant Changes in Soft Tissue Tumor Classification

^* Inadvertently omitted in the 2020 WCT.

^† Spindle cell/sclerosing rhabdomyosarcoma has been split into these 3 separate entries.

^‡ The category round cell sarcomas with EWSR1-non-ETS fusions has been split into NFATC2-rearranged sarcoma and PATZ1-rearranged sarcoma.

^§ The family of fibrogenic tumors that was listed under bone tumors in STB5 has been removed in STB6.

Adipocytic Tumors

One new tumor type is introduced as lipoblastoma-like tumor, a benign spindle cell neoplasm of mature and immature adipocytic differentiation sharing morphologic features of spindle cell lipoma, myxoid liposarcoma, and lipoblastoma (Tables 1 and 2).^3–6 It has a lobulated growth pattern, delineated by variably sized septa; an admixture of mature adipocytes, univacuolated and/or bivacuolated lipoblasts, and bland spindle cells; with variably myxoid to collagenous matrix and thin-walled plexiform vasculature (Fig. 1A).

The diagnostic criteria for atypical spindle cell/pleomorphic lipomatous tumors are clarified in this edition, and they are now separated into atypical spindle cell and atypical pleomorphic subtypes.⁷ Nonlipogenic tumors within the spectrum of well-differentiated liposarcoma and dedifferentiated liposarcoma are now distinguished based on mitotic rate: owing to survival differences, tumors with up to 4 mitoses per 10 HPF are classified as cellular well-differentiated liposarcoma (atypical lipomatous tumor), while tumors with 5 mitoses or more are classified as dedifferentiated liposarcoma (of note, HPF diameter was not indicated for most of these studies, so the number of mitoses/mm² cannot be accurately determined).⁸ The designation “low-grade dedifferentiated liposarcoma” is therefore no longer recommended. More precise grading parameters for myxoid liposarcoma are specified, with explicit distinction between low-grade and higher-grade disease. Higher-grade myxoid liposarcoma is defined by the presence of more cellular areas with round cells exceeding 5% of the tumor, usually accompanied by diminished myxoid matrix.

Fibroblastic and Myofibroblastic Tumors

Two new tumor types are included under this category as PRRX1-rearranged fibroblastic tumor^9,10 and nodular necrotizing fibroblastic tumor (see Tables 1 and 2). PRRX1-rearranged fibroblastic tumor is a benign spindle cell neoplasm characterized by PRRX1 rearrangements, most often with NCOA1 (Fig. 1B). While initially suggested to be a subtype of myxoinflammatory fibroblastic sarcoma, nodular necrotizing fibroblastic tumor is now recognized as a separate entity specified as a superficial mesenchymal neoplasm composed of epithelioid cells with a brisk inflammatory infiltrate and, in many cases, central necrosis, showing indolent behavior (Fig. 2).¹¹ Most of these lesions harbor YAP1::MAML2 fusions.

There were small changes in nomenclature: EWSR1::SMAD3-positive fibroblastic tumor was modified to SMAD3-rearranged fibroblastic tumor (anticipating the future identification of fusion partners involving other members of the FET family of genes), and the word “pleomorphic” was added to superficial CD34-positive pleomorphic fibroblastic tumor (given the importance of cytologic pleomorphism in both recognition of this tumor type and possible confusion with pleomorphic sarcomas). Calcifying fibrous tumor, inadvertently omitted from the 2020 classification, has been included in STB6. Tumors that resemble sclerosing epithelioid fibrosarcoma with MUC4 negativity and the presence of gene fusions involving YAP1 and KMT2A were co-classified with sclerosing epithelioid fibrosarcoma, recognizing that this may change as more outcome data are collected.^12–14 Notably, adult fibrosarcoma has been removed from the classification, as essentially all tumors diagnosed as adult fibrosarcoma in the past can now be reclassified as other sarcoma types using contemporary methods (eg, monophasic synovial sarcoma, malignant peripheral nerve sheath tumor, and the fibrosarcomatous variant of dermatofibrosarcoma protuberans). However, infantile fibrosarcoma (IFSC) remains in the classification, as it is a distinctive tumor type occurring in children with specific morphological and genetic abnormalities; when IFSC presents in the kidney, the most common and acceptable terminology is “cellular congenital mesoblastic nephroma.” Finally, undifferentiated pleomorphic sarcoma (UPS) has been moved from tumors of uncertain differentiation (where it was considered a subtype under the umbrella term of “undifferentiated soft tissue sarcoma”) to the section on fibroblastic and myofibroblastic tumors, since in many cases the tumor cells appear to show fibroblastic and sometimes myofibroblastic differentiation, despite the “undifferentiated” designation. UPS is still considered a diagnosis of exclusion. Low-grade, uniform and monomorphic spindle cell sarcomas should not be classified as UPS, as they increasingly seem to be resolving into other entities.

Fibrohistiocytic and Synovial Tumors

This chapter’s heading, “fibrohistiocytic tumors” in the 5th edition, is changed to “Fibrohistiocytic and synovial tumors” in STB6.

Two new tumor types are included here as chondroid synoviocytic neoplasm and keratin-positive giant cell-rich tumor (KPGCT) (seeTables 1 and 2). Chondroid synoviocytic neoplasm (a.k.a. “chondroid tenosynovial giant cell tumor” or “calcified chondroid mesenchymal neoplasm”) has a predilection for the temporomandibular joint region, is composed of varying amounts of large, eosinophilic synoviocytes, osteoclastic giant cells, hyaline cartilage, and calcified matrix (Fig. 3), and frequently harbors FN1 rearrangements.^15–19 KPGCT is a mesenchymal neoplasm of uncertain lineage, composed of multinucleated giant cells, mixed inflammatory cells, histiocytes, and a small number of keratin-positive mononuclear cells (Fig. 4A, B), harboring HMGA2::NCOR2 fusions.^20–23 Deep fibrous histiocytoma has been removed from this classification, since it is a subtype of cutaneous benign fibrous histiocytoma (dermatofibroma), which is included in the WHO classification of skin tumors.

Pericytic (Perivascular) Tumors

A new tumor type, SRF-rearranged myoid neoplasm, has been introduced (see Tables 1 and 2), encompassing a group of predominantly benign tumors exhibiting myoid or immature smooth muscle differentiation and characterized by SRF gene fusions with various partners (Fig. 4C, D).^24–26 In the previous 5th edition, a subset of these tumors was described as an “atypical cellular variant” of myofibroma.

Smooth Muscle Tumors

Inflammatory leiomyosarcoma has been omitted from this section, as tumors in this category are now designated as inflammatory rhabdomyoblastic tumor (see the Skeletal Muscle Tumors section).

Skeletal Muscle Tumors

Inflammatory rhabdomyoblastic tumor is introduced in this volume (see Tables 1 and 2), including tumors formerly designated inflammatory leiomyosarcoma. It is defined as an intermediate (rarely metastasizing) neoplasm, characterized by skeletal muscle differentiation, a marked lymphohistiocytic infiltrate (Fig. 4E, F), and near-haploidization.^27–30 Malignant progression to rhabdomyosarcoma can be seen and is characterized by high mitotic activity and often necrosis.³¹ Based on genetic features and differences in clinical behavior, spindle cell/sclerosing rhabdomyosarcoma has been split into 3 separate entities: fusion-associated spindle cell rhabdomyosarcomas and MYOD1-mutant spindle cell/sclerosing rhabdomyosarcoma are discussed in the soft tissue chapter, while TFCP2-rearranged rhabdomyosarcoma predominantly occurs in bone and is discussed in the bone chapter (see Tables 1 and 2). Fusion-associated spindle cell rhabdomyosarcomas are a heterogeneous group of sarcomas with skeletal muscle differentiation and fascicular spindle cell morphology, defined by recurrent pathognomonic fusions, including, among others, NCOA2 or CITED2, ZFP64, and VGLL3 as fusion partners.^32–34MYOD1-mutant spindle cell/sclerosing rhabdomyosarcoma is an aggressive subtype of rhabdomyosarcoma, characterized by fascicular spindle cell and/or sclerosing morphology and MYOD1 p.L122R mutation.^31,35–37 Ectomesenchymoma, an extremely rare and predominantly pediatric tumor, was removed as a separate entity from the classification; this lesion is now recognized as a subtype of embryonal rhabdomyosarcoma and referred to as “embryonal rhabdomyosarcoma with divergent neuroectodermal differentiation” based on the presence of intermixed neuroblastic elements.

Gastrointestinal Stromal Tumor

Succinate dehydrogenase-deficient gastrointestinal stromal tumor has been recognized as a separate category, given the distinct molecular pathogenesis, implications for possible familial syndromic associations, and differences in clinical behavior.^38–42

Chondro-Osseous Tumors

No significant changes were made to this section.

Peripheral Nerve Sheath Tumors

Epithelioid malignant peripheral nerve sheath tumor (EMPNST), previously considered a subtype of MPNST, is now recognized as a separate entity, based on its distinctive epithelioid morphology and specific molecular pathogenesis (loss of SMARCB1 [INI1] expression).^43,44

Tumors of Uncertain Differentiation

A large number of recently recognized tumor types are included for the first time in this volume, including OGT-rearranged mesenchymal neoplasm (formerly known as OGT-rearranged acral mesenchymal neoplasm) (Fig. 5),⁴⁵ acral fibrochondromyxoid tumor (AFCMT),⁴⁶GLI1-altered mesenchymal tumors,^47–49 superficial FET-ETS family neurocristic tumor,^50,51 pseudoendocrine sarcoma,^52,53 NUT-rearranged sarcoma,^54,55 and FET-CREB family epithelioid mesenchymal tumors (see Tables 1 and 2).^56–58 AFCMT is a benign mesenchymal neoplasm of uncertain differentiation arising in acral sites and composed of bland spindle or round cells arranged in a chondromyxoid stroma lobulated by fibrovascular septa (Fig. 6A, B). GLI1-altered mesenchymal tumors have variable clinical behavior, often nested epithelioid morphology and a rich capillary network (Fig. 6C-E), and are driven by fusions or amplification of GLI1. Superficial FET-ETS family neurocristic tumor is an indolent superficial neoplasm that shares similar fusion events with Ewing sarcoma (Fig. 7A, B). Pseudoendocrine sarcoma is a malignant neoplasm of uncertain lineage, predominantly arising in paravertebral soft tissues, morphologically resembling a well-differentiated neuroendocrine tumor (Fig. 7C, D), but lacking expression of keratins and neuroendocrine markers, while harboring CTNNB1 mutations. NUT-rearranged sarcoma is an aggressive malignant mesenchymal neoplasm characterized by heterogeneous morphology (Fig. 7E, F) and gene fusions involving NUTM1. FET-CREB family malignant epithelioid mesenchymal tumors typically involve mesothelial-lined cavities, show epithelioid morphology and epithelial marker expression (Fig. 8), and are characterized by fusions between EWSR1 or FUS genes with members of the CREB family of transcription factors (ATF1, CREB1, and CREM).

The former “emerging” category of NTRK-rearranged spindle cell neoplasms was expanded to kinase-altered spindle cell neoplasms, since it is now recognized that a wide range of kinase gene fusions (as well as point mutations) can be identified in this tumor class.^59–61PATZ1-rearranged sarcoma was introduced into this section; this tumor was included within round cell sarcomas with EWSR1-non-ETS fusions in the 5th edition. These tumors show more morphologic heterogeneity than round cell sarcomas, with round and spindle cell morphology, co-express myoepithelial and skeletal muscle markers, and are characterized by fusions involving EWSR1 and PATZ1. Two entities (atypical fibroxanthoma and ectopic hamartomatous thymoma) were no longer included, and the umbrella term “undifferentiated soft tissue sarcoma” is no longer recommended as a miscellaneous category for the group of tumors including undifferentiated pleomorphic sarcoma (moved to (myo)fibroblastic tumors; see above), undifferentiated spindle cell sarcoma, and undifferentiated round cell sarcoma.

VASCULAR TUMORS OF SOFT TISSUE AND BONE

The most significant change in this section is the nomenclature for lesions formerly known as hemangiomas and lymphangiomas, introducing the term vascular anomalies (and lymphatic malformations) to align the classification with the International Society for the Study of Vascular Anomalies (ISSVA).⁶² Spindle cell hemangioma was inadvertently omitted from the 2020 classification; it has been included in STB6. YAP1::TFE3 hemangioendothelioma has been separated from epithelioid hemangioendothelioma given the differences in histopathology, molecular pathogenesis, and clinical behavior (see Tables 1 and 2).⁶³YAP1::TFE3 hemangioendothelioma is a malignant vascular neoplasm composed of epithelioid endothelial cells that often display abundant eosinophilic cytoplasm and vasoformative features (Fig. 9A), characterized by YAP1::TFE3 fusion. Patients with this tumor type have a more favorable clinical outcome than those with conventional epithelioid hemangioendothelioma.

UNDIFFERENTIATED SPINDLE AND SMALL ROUND CELL SARCOMAS

Given the fact that some of these high-grade sarcomas show not only round cell but also spindle cell morphology, the chapter name has been modified accordingly. The tumors included in this section are Ewing sarcoma, NFATC2-rearranged sarcoma, sarcomas with BCOR genetic alterations, and CIC-rearranged sarcoma. As mentioned above, the category round cell sarcomas with EWSR1-non-ETS fusions in the 5th edition has been split into NFATC2-rearranged sarcoma (included in this section)^64–66 and PATZ1-rearranged sarcoma (included under tumors of uncertain differentiation in the soft tissue tumors chapter). NFATC2-rearranged sarcoma is a round and spindle cell sarcoma with fibrohyaline stroma, associated with EWSR1::NFATC2 or FUS::NFATC2 fusions.

BONE TUMORS

Significant Changes in Bone Tumor Classification

Chondrogenic Tumors

A multidisciplinary approach for diagnosing these lesions with radiological correlation is emphasized in this edition . In the 5th edition, the terms “atypical cartilaginous tumor” and “chondrosarcoma, grade 1” were further defined: cartilaginous tumors in the appendicular skeleton (long and short tubular bones) are diagnosed as atypical cartilaginous tumors, and the term “chondrosarcoma, grade 1,” is reserved for tumors of the axial skeleton, including the pelvis, scapula, and skull base (flat bones), reflecting the poorer clinical outcome of these tumors at these sites.⁶⁷ Using different terminology for tumors with identical histomorphology could be considered counterintuitive and controversial. However, this terminology has the dual benefit of being simple in application and reflecting the worse outcome for tumors at these sites where there is a need for more extensive surgery.⁶⁷ Consequently, this terminology is further endorsed in the current classification. Chondromesenchymal hamartoma of the chest wall, based on the presence of cartilage, is discussed in STB6 under chondrogenic tumors instead of other tumors of bone as in STB5. In STB6, based on recent publications,⁶⁸ it is now recognized that a very small subset of chondroblastomas is malignant. These tumors show atypia and permeation, occur in the flat bones of older individuals, and are H3K36M positive by IHC.

Osteogenic Tumors

Benign osteogenic tumors include osteoma, osteoid osteoma, and osteoblastoma. Osteosarcoma is the most common malignant bone sarcoma, and multiple types as well as morphological patterns are distinguished based on location as well as morphology. No changes were made in their classification as compared to the 5th edition.

Fibrogenic Tumors

The category of “fibrogenic tumors” has been deleted from the bone tumor classification. Desmoplastic fibroma of bone was moved to “other tumors of bone.” Fibrosarcoma of bone, formerly considered a diagnosis of exclusion, was removed (similar to the soft tissue chapter), since most of these seem to represent dedifferentiated chondrosarcoma or leiomyosarcoma of bone, or rare bone presentations of soft tissue tumors such as solitary fibrous tumor, kinase-altered spindle cell neoplasms, or synovial sarcoma.

Osteoclastic Giant Cell-Rich Tumors

While many bone tumors can contain osteoclasts, they are a defining feature in giant cell tumor of bone, aneurysmal bone cyst, and nonossifying fibroma. Brown tumor of hyperparathyroidism, which was shown to be neoplastic when KRAS mutations were found to be necessary for their development, in addition to elevated parathyroid hormone (PTH) levels,⁶⁹ is included as a separate entity in STB6. It is defined as a benign spindle cell neoplasm with intermingled osteoclastic giant cells (Fig. 9B), occurring in the context of hyperparathyroidism.

In the previous edition, the occurrence of H3.3 p.G35W (G34W) in bone sarcomas (osteosarcoma, undifferentiated pleomorphic sarcoma) without associated giant cell tumor histology was acknowledged, suggesting a relationship to giant cell tumor of bone. More recent evidence showed that undifferentiated pleomorphic sarcoma or osteosarcoma with H3.3 p.G35 (G34) mutations show similar molecular and methylation profiles and thus may represent malignant giant cell tumors of bone.⁷⁰ However, studies with larger cohorts are needed to confirm this association and direct clinical management.

Notochordal Tumors

Notochordal tumors include benign notochordal cell tumor, conventional chordoma (including chondroid chordoma), dedifferentiated chordoma, and poorly differentiated chordoma. No changes were made in their classification as compared to the 5th edition.

Other Tumors of Bone

In this 6th edition, “osteofibrous dysplasia (OFD)-like adamantinoma” has been renamed as “atypical OFD” and is now considered a locally aggressive subtype of OFD. This better reflects the nonmalignant behavior of atypical OFD and should avoid overtreatment of these tumors in young patients.⁷¹ The diagnosis can nevertheless be difficult, and interobserver variability is high. TFCP2-rearranged rhabdomyosarcoma is a novel type of high-grade sarcoma with skeletal muscle differentiation (Fig. 9C), characterized by the fusion of TFCP2 to EWSR1 or FUS, with a predilection for the maxillofacial bones.⁷² This tumor is now included as a new bone tumor entity (see Tables 1 and 2).

HEMATOPOIETIC AND DENDRITIC CELL NEOPLASMS OF SOFT TISSUE AND BONE

Significant Changes in Hematopoietic and Dendritic Cell Neoplasms

Based on the approach taken by STB6 of describing only hematopoietic neoplasms that arise in nonmucosal extranodal soft tissues or involve bone primarily, this chapter includes plasmacytoma; diffuse large B-cell lymphoma, not otherwise specified (NOS) involving bone; Langerhans cell histiocytosis; Erdheim-Chester disease; follicular dendritic cell sarcoma; and Rosai-Dorfman disease.

Myeloid neoplasms and other medullary proliferations arising within the bone marrow compartment are excluded from this chapter. However, it should also be noted that virtually any hematolymphoid neoplasm may secondarily involve soft tissue and/or bone in the setting of locally extensive or systemic disease. Accordingly, diagnostic evaluation requires integration of morphological, immunophenotypic, and molecular findings with appropriate imaging and clinical assessment to determine the extent of involvement and to establish whether the lesion represents a primary neoplasm of soft tissue or bone.

GENETIC TUMOR SYNDROMES OF SOFT TISSUE AND BONE

Significant Changes in Genetic Tumor Syndromes

AD indicates autosomal dominant; AR, autosomal recessive; PZ, postzygotic.

^* OMIM indicates Online Mendelian Inheritance in Man (https://www.omim.org).

Germline (constitutional) pathogenic variants associated with an increased risk of developing soft tissue and/or bone tumors are being identified in a growing list of genes through the application of sequencing technology such as massively parallel DNA sequencing (Table 3). These tumor-predisposing genetic variants often have additional phenotypic consequences, resulting in clinically recognizable syndromes. As germline pathogenic variants are often inherited from one of the parents, it is important to recognize such tumor-predisposing syndromes to screen at-risk individuals in affected families for referral to genetic counseling and implementation of guideline-based surveillance for early cancer detection. While most of these syndromes demonstrate Mendelian inheritance, patients with disorders caused by postzygotic mutations have now been recognized and may need distinct forms of therapy and personalized follow-up. The study of germline tumor-predisposing variants may shed light on the pathogenesis of sporadic tumors.

This chapter provides detailed descriptions of 6 syndromes associated with predisposition to the development of bone or soft tissue tumors (see Table 3). These well-characterized syndromes are included because the tumor manifests in the bone or soft tissues as part of the syndrome at high frequency and is a primary outcome of the genetic alteration underlying that syndrome, often with neoplasm features that are different from those of their sporadic counterparts.

Changes in STB6 related to genetic tumor syndromes include the removal of Rothmund-Thomson syndrome and Werner syndrome from having their own sections in the 5th edition to now only being mentioned in a table in the introduction. Paget disease of bone was selected to move from the introductory table in the 5th edition to currently having an extended section.

CONCLUSION

The 6th edition of the soft tissue and bone tumors volume provides an updated classification and comprehensive overview of tumors arising in soft tissue and bone based on the current best available evidence. It has attempted to meet global requirements while balancing scientific advances.

Acknowledgments

The authors gratefully acknowledge support extended by all in the WHO Classification of Tumors (WCT) group and the contributions made by the WCT subcommittees: Genetics and Genomics, Computational Pathology, WCT/LMIC Liaison, Tumor Harmonization, Imaging and Radiology, and Tumor Defining and Clarification. The figures are reprinted with permission from: WHO Classification of Tumours Editorial Board. Soft tissue and bone tumours. Lyon (France): International Agency for Research on Cancer; 2026. (WHO classification of tumours series, 6th ed.; vol. 3). Available from: https://tumourclassification.iarc.who.int/chapters/87.