Table 2.

Osteosarcoma subtypes

Subtype	Location	Grade	Histology
Low-grade central osteosarcoma	Medulla	Low grade	Spindle cells with low-grade nuclear atypia and well-formed neoplastic woven bone trabeculae, often 12q13 amplification
Parosteal osteosarcoma	Surface	Low grade	Spindle cell proliferation, often with cartilaginous differentiation, and 12q13 amplification
Periosteal osteosarcoma	Surface (typically underneath the periosteum)	Intermediate grade	Predominantly chondroblastic bone-forming sarcoma
Conventional osteosarcoma	Medulla	High grade	High-grade sarcoma in which the tumour cells produce bone. Tumour cells can be fibroblastic, chondroblast- or osteoblast-like
Fibroblastic Chondroblastic Osteoblastic
Small-cell osteosarcoma	Medulla	High grade	Small cells with scant cytoplasm, associated with variable osteoid formation; may resemble Ewing sarcoma
Telangiectatic osteosarcoma	Medulla	High grade	Osteosarcoma composed of blood-filled or empty cystic spaces closely simulating aneurysmal bone cyst
High-grade surface osteosarcoma	Surface	High grade	Similar to conventional osteosarcoma