Abone sarcoma is aprimarymalignantbone tumour, a type ofsarcoma that starts in thebones.^[1] This is in contrast to mostbone cancers that are secondary having developed as ametastasis from another cancer. Bone sarcomas are rare, and mostly affect thelegs. The other type of sarcoma is asoft-tissue sarcoma.

There are three main types of bone sarcoma based ontissue type – anosteosarcoma, aEwing's sarcoma, and achondrosarcoma.^[1]

The three main types of bone sarcoma are anosteosarcoma, most frequently found of the three;Ewing's sarcoma, and achondrosarcoma.^[2] There are many subtypes of these.

An osteosarcoma is predominantly found in childhood and adolescence.^[1] They are primarily found inlong bones, and may be secondary tumours.^[3] Osteosarcomas are composed ofmesenchymal cells that produce immature bone.^[4] The tumour cells are unique in that they produce immatureosteoid.^[3]

Ewing's sarcoma is the next most commonly found sarcoma in adolescents and young adults. Ewing's is highly aggressive, typically developing from themedullary cavity of a bone with cells invading theHaversian system.^[5] Animmunohistochemistry test shows the tumour as having small rounded blue cells.^[6][7] The cells express high levels ofCD99.^[5]

Achondrosarcoma is the type of bone cancer that starts in thecartilage cells. It is the most common type found in adults. Unlike the other types it is rarely found in those under the age of twenty. Most chondrosarcomas develop in thepelvis, legs or arms. Benign counterparts are known asenchondromas. Chondrosarcomas are classified by grade as a measurement of their growth rate – I, II, and III. The lower the grade the slower the rate of growth. Grade III are the most aggressive, and are liable tospread.^[8]

Subtypes of chondrosarcomas have different features and differentoutlooks, they include:^{[citation needed]}

Dedifferentiated

Dedifferentiated chondrosarcomas can change in part to cells that are like those of an osteosarcoma for example which has a faster rate of growth.

Clear cell

Clear cell chondrosarcomas are rare, slow-growing, and seldom spread.

Mesenchymal

Mesenchymal chondrosarcomas can grow quickly but unlike other types may respond toradiotherapy, andchemotherapy.^[8] They have densely packed small round blue cells like those in Ewing's sarcoma.^[9]Type II collagen can help distinguish it from other tumours.^[10]