Classification of Primary Bone Lesions

Abstract

Primary bone tumors are classified on the base of their histological differentiation, as reported in the following table. Thay are divided into “benign” (with a limited capacity of local recurrence), “intermediate” (locally aggressive: local recurrence, also in a destructive way; rarely metastasizing: as above also with possible distant metastasis in occasional cases, not predictable on the basis of the morphology), and “malignant,” the latter furtherly divided into low-grade and high-grade malignant.

Primary bone tumors are classified on the base of their histological differentiation, as reported in the following table. Thay are divided into “benign” (with a limited capacity of local recurrence), “intermediate” (locally aggressive: local recurrence, also in a destructive way; rarely metastasizing: as above also with possible distant metastasis in occasional cases, not predictable on the basis of the morphology), and “malignant,” the latter furtherly divided into low-grade and high-grade malignant.

Classification of primary bone tumors (WHO 2013)

Histogenesis	Benign	Intermediate (locally aggressive and/or rarely metastasizing)	Malignant [(∗) low-grade lesions if not dedifferentiated]
Fibrogenic and fibrohistiocytic	Histiocytic fibroma Benign fibrous histiocytoma	Desmoplastic fibroma	Fibrosarcoma
Chondrogenic	Osteochondroma Hemimelic epiphyseal dysplasia Enchondroma Periosteal chondroma Osteochondromyxoma Subungual exostosis Bizarre parosteal osteochondromatous proliferation Synovial chondromatosis	Chondromyxoid fibroma Chondrosarcoma grade 1 Chondroblastoma Fibrocartilaginous mesenchymoma	Chondrosarcoma grade 2 Chondrosarcoma grade 3 Dedifferentiated chondrosarcoma Mesenchymal chondrosarcoma Peripheral chondrosarcoma (∗) Periosteal chondrosarcoma (∗) Clear cell condrosarcoma (∗)
Osteogenic	Osteoma Osteoid osteoma	Osteoblastoma	Low-grade central osteosarcoma (∗) Conventional osteosarcoma Telangiectatic osteosarcoma Small-cell osteosarcoma Secondary osteosarcoma Parosteal osteosarcoma (∗) Periosteal osteosarcoma (∗) High-grade surface osteosarcoma
Osteoclastic giant cell rich	Giant cell reparative granuloma	Giant cell tumor of bone	Malignancy in giant cell tumor
Vascular	Hemangioma Lymphangioma	Epithelioid hemangioma	Epithelioid and other hemangioendothelioma (∗) Angiosarcoma
Nervous	Schwannoma Neurofibroma		MPNST
Lipogenic	Lipoma		Liposarcoma
Myogenic	Leiomyoma		Leiomyosarcoma
Notochordal	Benign notochordal cell tumor		Chordoma (∗)
Hematopoietic neoplasms			Primary non-Hodgkin and Hodgkin lymphoma Plasmocytoma of bone/plasma cell myeloma
Tumors of undefined neoplastic nature/miscellaneous tumors	Simple bone cyst Fibrous dysplasia Osteofibrous dysplasia Chondromesenchymal hamartoma Rosai-Dorfman disease	Aneurysmal bone cyst Langerhans cell histiocytosis Erdheim-Chester disease	Adamantinoma (∗) Ewing sarcoma Undifferentiated pleomorphic sarcoma