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Classification of bone tumours

Osteosarcoma is the most frequent primary malignant tumour of bone, deriving from primitive bone-forming mesenchyme and characterized by the production of osteoid tissue or immature bone by the malignant proliferating spindle cell stroma.

The World Health Organization's histologic classification of bone tumours separates the osteosarcomas into central (medullary) and surface (peripheral) tumours and recognizes a number of subtypes within each group (table 1).

The most common pathologic subtype is conventional high-grade central osteosarcoma. It accounts for 80-90% of all osteosarcomas and is characterized by areas of necrosis, atypical mitoses and malignant cartilage.

Its most frequent subtypes are osteoblastic, chondroblastic and fibroblastic osteosarcomas.

Table 1: Osteosarcoma subtypes within central and surface tumours

CENTRAL (MEDULLARY)

a. Conventional high-grade central osteosarcoma b. Telangiectatic osteosarcoma c. Intraosseous well-differentiated (low-grade) osteosarcoma d. Small cell osteosarcoma

SURFACE (PERIPHERAL)

a. Parosteal (juxtacortical) well-differentiated (low-grade) osteosarcoma b. Periosteal osteosarcoma - low- to intermediate-grade osteosarcoma c. High-grade surface osteosarcoma

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