This information has been written for patients, their families and friends and the general public to help them understand more about a form of primary bone cancer known as osteosarcoma. This page will detail what an osteosarcoma is and how osteosarcoma is diagnosed and treated.

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What is osteosarcoma?

Osteosarcoma is the most common type of primary bone cancer in children and young people, and the second most common overall after chondrosarcoma.

Osteosarcoma starts when one bone cell becomes abnormal and grows out of control to form a lump of cancerous tissue known as a tumour. The cells in the tumour still act like bone, in that they try to create new bone as they grow and divide. If a pathologist can see new bone (known as osteoid) in a tumour sample under the microscope, this helps to confirm a diagnosis of osteosarcoma.

'Osteo' comes from an ancient Greek word for bone. 'Sarcoma' is the name given to cancers that start in connective or supporting tissues, such as bone, fat, cartilage, blood vessels and muscle.

The majority of osteosarcomas arise from a single place within the area of a long bone known as the metaphysis or 'neck' of a long bone. The metaphysis contains the area of the bone where cells are growing and dividing, this is called the epiphyseal plate.

The long bones of the skeleton are bones that are longer than they are wide, for example the thigh bone (femur) or the upper arm bone (humerus). Half of osteosarcoma cases occur in the long bones of the lower body.

Figure 1 shows what is inside a long bone, and where osteosarcoma can arise.


The three areas most often affected by osteosarcoma are:

  • The lower thigh bone nearest to the knee (distal femur)
  • The upper shin bone nearest to the knee (proximal tibia)
  • The upper arm bone nearest to the shoulder (proximal humerus)

Other bones can be affected such as the jaw, spine and the pelvis.

Tumours found in the bones of the face, skull and spine are more common in older osteosarcoma patients than younger osteosarcoma patients.

Figure 2 shows where in the skeleton osteosarcoma most often occurs.