WHO classification of tumors of bone

The World Health Organization (WHO) classification of bone tumors is the most widely used pathologic classification system for such disorders. The current revision, part of the 5^th edition of the WHO series, was published in 2020 and is reflected in the article below ¹.

Classification

Chondrogenic tumors

• osteochondroma

• periosteal chondroma

• enchondroma

• chondromyxoid fibroma

• osteochondromyxoma

• subungual exostosis

• bizarre parosteal osteochondromatous proliferation

• synovial chondromatosis

• chondroblastoma

• central atypical cartilaginous tumor / chondrosarcoma (grade 1)

• secondary peripheral atypical cartilaginous tumor / chondrosarcoma (grade 1)

• central chondrosarcoma (grades 2-3)

• secondary chondrosarcoma (grade 2-3)

• periosteal chondrosarcoma

• dedifferentiated chondrosarcoma

• mesenchymal chondrosarcoma

• clear cell chondrosarcoma

Osteogenic tumors

• osteoma

• osteoid osteoma

• osteoblastoma

• low-grade central osteosarcoma

• osteosarcoma

  • conventional osteosarcoma

  • telangiectatic osteosarcoma

  • small cell osteosacroma

• parosteal osteosarcoma

• periosteal osteosarcoma

• high-grade surface osteosarcoma

• secondary osteosarcoma

Fibrogenic tumors

• desmoplastic fibroma of bone

• fibrosarcoma of bone

Vascular tumors

• hemangioma

• epithelioid hemangioma

• epithelioid hemangioendothelioma

• angiosarcoma

Osteoclastic giant cell-rich tumors

• aneurysmal bone cyst

• giant cell tumor of bone

• non-ossifying fibroma 

Notochordal tumors

• benign notochordal cell tumor

• chordoma

• dedifferentiated chordoma

• poorly differentiated chordoma

Other mesenchymal tumors of bone

• chondromesenchymal hamartoma

• osteofibrous dysplasia

• adamantinoma

• simple bone cyst

• fibrocartilaginous mesenchymoma

• fibrous dysplasia

• lipoma of bone

• liposarcoma

• leiomyosarcoma

• undifferentiated pleomorphic sarcoma

• bone metastasis

Hematopoietic neoplasms

• solitary plasmacytoma of bone

• primary non-Hodgkin lymphoma of bone

• Langerhans cell histiocytosis

• Erdheim-Chester disease

• Rosai-Dorfman disease

Changes from the prior version

New entities and variants

Newly introduced entities include the following ¹:

• chondrogenic tumors

  • secondary peripheral atypical cartilaginous tumor / chondrosarcoma (grade 1)

  • secondary chondrosarcoma (grade 2-3)

• osteogenic tumors

  • secondary osteosarcoma

• notochordal tumors

  • dedifferentiated chordoma

  • poorly differentiated chordoma

• other mesenchymal tumors of bone

  • fibrocartilaginous mesenchymoma

  • bone metastases

Other changes

• Ewing sarcoma has been moved to a whole different chapter together with several other new entities of undifferentiated small round cell sarcomas of soft tissue and bone

• clearer differentiation of central and secondary peripheral chondrosarcoma variants:

  • central atypical cartilaginous tumor / chondrosarcoma (grade 1)

  • secondary peripheral atypical cartilaginous tumor / chondrosarcoma (grade 1)

  • central chondrosarcoma (grades 2-3)

  • secondary chondrosarcoma (grade 2-3)

• non-ossifying fibroma and aneurysmal bone cyst have been classified as osteoclastic giant cell-rich tumors

• Langerhans cell histiocytosis, Erdheim-Chester disease and Rosai-Dorfman disease have been classified as hematopoietic neoplasms of bone

• myogenic, lipogenic, epithelial tumors and tumors of undefined neoplastic nature have been classified as other mesenchymal tumors of bone which also includes undifferentiated pleomorphic sarcoma

• giant cell lesion of the small bones has been removed as a separate entity

See also

• WHO classification of tumors of soft tissue

• undifferentiated small round cell sarcomas of bone and soft tissue

• genetic tumor syndromes of soft tissue and bone