Bone & joints
General
WHO classification
Author: Borislav A. Alexiev, M.D.
Editorial Board Members: Nasir Ud Din, M.B.B.S., Jose G. Mantilla, M.D.
Last author update: 24 February 2022
Last staff update: 21 December 2023
Copyright: 2022, PathologyOutlines.com, Inc.
PubMed Search: Bone tumors - WHO classification [title]
Table of Contents
Definition / general | Major updates | WHO (2020) | Microscopic (histologic) images | Additional references | Board review style question #1 | Board review style answer #1 | Board review style question #2 | Board review style answer #2Cite this page: Alexiev BA. WHO classification. PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/boneWHOclass.html. Accessed April 24th, 2024.
Definition / general
- WHO classification of bone tumors is regarded as the gold standard reference for diagnosis of bone tumors and provides an indispensable international resource for those involved in the care of patients with bone cancer or in cancer research, including pathologists, oncologists and surgeons (Adv Anat Pathol 2021;28:119)
Major updates
- Selected tumors removed in the 2020 WHO classification of bone tumors:
- Benign fibrous histiocytoma
- Giant cell lesion of the small bones
- Leiomyoma
- Liposarcoma
- Selected tumors reclassified in the categorization of 2020 WHO classification of bone tumors:
- Aneurysmal bone cyst (tumor categorization: osteoclastic giant cell rich tumor)
- Nonossifying fibroma (tumor categorization: osteoclastic giant cell rich tumor)
- Chondromesenchymal hamartoma of chest wall (tumor categorization: other mesenchymal tumor of bone)
- Simple bone cyst (tumor categorization: other mesenchymal tumor of bone)
- Fibrous dysplasia (tumor categorization: other mesenchymal tumor of bone)
- Osteofibrous dysplasia (tumor categorization: other mesenchymal tumor of bone)
- Adamantinoma (tumor categorization: other mesenchymal tumor of bone)
- Pleomorphic sarcoma, undifferentiated (tumor categorization: other mesenchymal tumor of bone)
- Langerhans cell histiocytosis (tumor categorization: hematopoietic neoplasm of bone)
- Erdheim-Chester disease (tumor categorization: hematopoietic neoplasm of bone)
- Rosai-Dorfman disease (tumor categorization: hematopoietic neoplasm of bone)
- Ewing sarcoma (tumor categorization: undifferentiated small round cell sarcoma of bone and soft tissue)
- Selected new tumor entities and subtypes in the 2020 WHO classification of bone tumors:
- Chondrogenic tumors
- The following new entities are considered in the new classification:
- Subungual exostosis
- Bizarre parosteal osteochondromatous proliferation
- Osteochondromyxoma
- Central atypical cartilaginous tumor / chondrosarcoma grade 1
- Secondary peripheral atypical cartilaginous tumor / chondrosarcoma grade 1
- The terminology atypical cartilaginous tumor (ACT) was introduced as a synonym for chondrosarcoma grade 1 (CS1) and classified as intermediate (locally aggressive) to reflect the clinical behavior of well differentiated / low grade lesions (Adv Anat Pathol 2021;28:119)
- Cartilaginous tumors in the appendicular skeletons (long and short tubular bones) should be termed ACTs, while the term CS1 should be 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 (Adv Anat Pathol 2021;28:119)
- Benign
- Subungual exostosis (Arch Pathol Lab Med 2022;146:60)
- Bizarre parosteal osteochondromatous proliferation (Arch Pathol Lab Med 2022;146:60)
- Osteochondromyxoma (J Bone Oncol 2016;5:194)
- Intermediate (locally aggressive)
- Atypical cartilaginous tumor (J Am Acad Orthop Surg 2021;29:553)
- The following new entities are considered in the new classification:
- Notochordal tumors
- 1 new entity is considered in the new classification:
- Malignant
- Poorly differentiated chordoma (Ann Diagn Pathol 2021;55:151809)
- Malignant
- 1 new entity is considered in the new classification:
- Other mesenchymal tumors of bone
- 3 new entities are considered in the new classification:
- Benign
- Chondromesenchymal hamartoma of chest wall (Diagn Pathol 2020;15:53)
- Hibernoma (Skeletal Radiol 2014;43:939)
- Malignant
- Dedifferentiated adamantinoma (Int J Surg Pathol 2019;27:193)
- Benign
- 3 new entities are considered in the new classification:
- Undifferentiated small round cell sarcoma of bone and soft tissue
- This new section contains not only the prototypical round cell sarcoma named Ewing sarcoma but also 3 distinct subsets that differ from Ewing sarcoma clinically, pathologically and molecularly (Pathologica 2021;113:70):
- Round cell sarcomas with EWSR1 gene fusion with non-ETS family members (Virchows Arch 2020;476:109, Am J Surg Pathol 2019;43:1112, Am J Surg Pathol 2019;43:220, Mod Pathol 2019;32:1593)
- CIC rearranged sarcomas (Genes Chromosomes Cancer 2012;51:207, Am J Surg Pathol 2017;41:941)
- BCOR rearranged sarcomas (Am J Surg Pathol 2018;42:604)
- This new section contains not only the prototypical round cell sarcoma named Ewing sarcoma but also 3 distinct subsets that differ from Ewing sarcoma clinically, pathologically and molecularly (Pathologica 2021;113:70):
- Chondrogenic tumors
WHO (2020)
-
Chondrogenic tumors ICD-O
- Benign
- Subungual exostosis9213/0
- Bizarre parosteal osteochondromatous proliferation9212/0
- Periosteal chondroma9221/0
- Enchondroma9220/0
- Osteochondroma9210/0
- Chondroblastoma, NOS9230/0
- Chondromyxoid fibroma9241/0
- Osteochondromyxoma9211/0
- Intermediate (locally aggressive)
- Chondromatosis, NOS9220/1
- Atypical cartilaginous tumor9222/1
- Malignant
- Chondrosarcoma, grade 19222/3
- Chondrosarcoma, grade 29220/3
- Chondrosarcoma, grade 39220/3
- Periosteal chondrosarcoma9221/3
- Clear cell chondrosarcoma9242/3
- Mesenchymal chondrosarcoma9240/3
- Dedifferentiated chondrosarcoma9243/3
-
Osteogenic tumors ICD-O
- Benign
- Osteoma, NOS9180/0
- Osteoid osteoma9191/0
- Intermediate (locally aggressive)
- Osteoblastoma, NOS9200/1
- Malignant
-
Fibrogenic tumors ICD-O
- Intermediate (locally aggressive)
- Desmoplastic fibroma8823/1
- Malignant
- Fibrosarcoma, NOS8810/3
-
Vascular tumors ICD-O
- Benign
- Hemangioma, NOS9120/0
- Intermediate (locally aggressive)
- Epithelioid hemangioma9125/0
- Malignant
- Epithelioid hemangioendothelioma, NOS9133/3
- Angiosarcoma9120/3
-
Osteoclastic giant cell rich tumors ICD-O
- Benign
- Aneurysmal bone cyst9260/0
- Nonossifying fibroma8830/0
- Intermediate (locally aggressive, rarely metastasizing)
- Malignant
-
Notochordal tumors ICD-O
- Benign
- Benign notochordal tumor9370/0
- Malignant
-
Other mesenchymal tumors of bone ICD-O
- Benign
- Chondromesenchymal hamartoma of chest wall
- Simple bone cyst
- Fibrous dysplasia8818/0
- Lipoma, NOS 8850/0
- Hibernoma8880/0
- Intermediate (locally aggressive)
- Osteofibrous dysplasia-like adamantinoma9261/1
- Mesenchymoma, NOS8990/1
- Malignant
- Adamantinoma of long bones9261/3
- Leiomyosarcoma, NOS 8890/3
- Pleomorphic sarcoma, undifferentiated8802/3
-
Hematopoietic neoplasms of bone ICD-O
- Plasmacytoma of bone9731/3
- Malignant lymphoma, non-Hodgkin, NOS9591/3
- Hodgkin disease, NOS9650/3
- Diffuse large B cell lymphoma, NOS9680/3
- Follicular lymphoma, NOS9690/3
- Marginal zone B cell lymphoma, NOS9699/3
- T cell lymphoma, NOS9702/3
- Anaplastic large cell lymphoma, NOS9714/3
- Malignant lymphoma, lymphoblastic, NOS9727/3
- Burkitt lymphoma, NOS9687/3
- Langerhans cell histiocytosis, NOS9751/1
- Langerhans cell histiocytosis, disseminated9751/3
- Erdheim-Chester disease9749/3
-
Undifferentiated small round cell sarcoma of bone and soft tissue ICD-O
Microscopic (histologic) images
Contributed by Borislav A. Alexiev, M.D.
Enchondroma
Chondrosarcoma
Dedifferentiated chondrosarcoma
Mesenchymal chondrosarcoma
Low grade osteosarcoma
Osteosarcoma
Aneurysmal bone cyst
Chondroblastoma
Giant cell tumor of bone
Nonossifying fibroma
Conventional chordoma
Additional references
Board review style question #1
Central atypical cartilaginous tumor / chondrosarcoma grade 1 is a locally aggressive, hyaline cartilage producing neoplasm arising in the medulla of bone. The term atypical cartilaginous tumor should be reserved for tumors arising in which of the following anatomical sites?
- Chest wall
- Long and short tubular bones
- Pelvis
- Scapula
- Skull base
Board review style answer #1
B. Long and short tubular bones. Cartilaginous tumors in the appendicular skeletons (long and short tubular bones) should be termed atypical cartilaginous tumors, while the term chondrosarcoma grade 1 should be 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.
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Reference: Bone tumors - WHO classification
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Reference: Bone tumors - WHO classification
Board review style question #2
The histologic pattern shown above would be most commonly expected in which of the following bone tumors listed in WHO 2020?
- Chondrosarcoma, grade 1
- Chordoma
- Low grade osteosarcoma
- Mesenchymal chondrosarcoma
- Osteosarcoma
Board review style answer #2
E. Osteosarcoma. Note highly atypical spindle cells producing lace-like unmineralized matrix (osteoid).
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Reference: Bone tumors - WHO classification
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Reference: Bone tumors - WHO classification
