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WHO classification



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PubMed Search: Bone tumors - WHO classification [title]

Borislav A. Alexiev, M.D.
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Cite this page: Alexiev BA. WHO classification. PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/boneWHOclass.html. Accessed December 3rd, 2022.
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:
WHO (2020)







Microscopic (histologic) images

Contributed by Borislav A. Alexiev, M.D.
Enchondroma

Enchondroma

Chondrosarcoma

Chondrosarcoma

Dedifferentiated chondrosarcoma

Dedifferentiated chondrosarcoma

Mesenchymal chondrosarcoma

Mesenchymal chondrosarcoma

Low grade osteosarcoma

Low grade osteosarcoma

Osteosarcoma

Osteosarcoma


Aneurysmal bone cyst

Aneurysmal bone cyst

Chondroblastoma

Chondroblastoma

Giant cell tumor of bone

Giant cell tumor of bone

Nonossifying fibroma

Nonossifying fibroma

Conventional chordoma

Conventional chordoma

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?

  1. Chest wall
  2. Long and short tubular bones
  3. Pelvis
  4. Scapula
  5. 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
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?

  1. Chondrosarcoma, grade 1
  2. Chordoma
  3. Low grade osteosarcoma
  4. Mesenchymal chondrosarcoma
  5. 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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