What is osteosarcoma?
This information has been written for patients, their families and friends and the general public to help you understand more about osteosarcoma: what it is and the different types.
Osteosarcoma is the most common type of primary bone cancer. It starts when bone cells become abnormal, growing out of control to form a lump of cancerous tissue known as a tumour. The cancerous tissue consists of abnormal cells that are attempting to make bone. Being able to see this abnormal bone under a microscope helps to confirm a diagnosis of osteosarcoma.
'Osteo' comes from an ancient Greek word for bone and a '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 (meta-FEE-siss), which contains the growing areas of the bone called the epiphyseal (epi-FEE-see-al) plate. The site at which the cancer starts is known as the primary tumour site. A long bone is very much longer than it is wide. The best examples being the bones of the limbs, for example, the thigh bone (femur) or the upper arm bone (humerus), see figure 1.
Figure 1. Basic Anatomy of a Long Bone.
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) and the upper arm bone nearest to the shoulder (proximal humerus). Other bones can be affected such as the jaw, spine and the pelvis, see figure 2. Tumours found in the bones of the face, skull and spine are more common in older patients.
Figure 2. Main Tumour Sites for osteosarcoma
Very rarely, osteosarcoma can start in more than one bone at the same time; this is called multi-focal osteosarcoma.
Osteosarcoma usually behaves in an aggressive manner, which means it can spread in the bloodstream from or through the bone in which it starts to other places in the body. The most common place for it to spread to is the lungs. Osteosarcoma can also spread to other places in the body including other bones. Because osteosarcoma spreads at an early stage, as well as treatment to the site of the primary tumour, patients need treatment to the whole body; this is called systemic (sis-TEH-mik) treatment.
When looked at under the microscope, all osteosarcomas can be seen to consist of abnormal cells that are 'trying' to make bone. There are five main subtypes of osteosarcoma.
- Usually, the cancer cells look like bone forming cells. These cells are called osteoblasts and so this type of osteosarcoma is known as 'osteoblastic osteosarcoma.'
- Sometimes, the cells look different under the microscope. If the cancer is trying to make cartilage as well as bone then the tumour is called 'chondroblastic (KON-dro-blast-ick) osteosarcoma.' Cartilage is tissue that covers and cushions the ends of bones, see figure 1.
- If there is only a small amount of bone being made by the cancerous cells then the tumour may be called 'fibroblastic osteosarcoma.'
- If there are lots of abnormal blood vessels in the tumour as well as bone forming cells then the tumour is called 'telangiectatic (teh-LAN-jee-ek-TAT-ick) osteosarcoma.'
- Some osteosarcomas contain small round cells and are called 'small cell osteosarcoma.' These can sometimes be difficult to tell from other tumours, which contain small round cells.
These five subtypes above account for about 90% of osteosarcomas and are all treated in the same way. Mostly these osteosarcomas start inside the bone and are called 'high grade.' High grade means that when the cells of the tumour are looked at under a microscope, many cells are in the process of dividing. This means the tumour behaves in an aggressive manner. As a result, they can spread to other sites in the body at an early stage.
Sometimes, osteosarcoma can start either on or close to the surface of bone. Some of these tumours have the same high grade appearance (cells are dividing rapidly) as the common subtypes above and are treated in the same way with a combination of surgery and chemotherapy drugs.
- Other types can be less aggressive (low grade) and may require surgery alone. These may be called 'parosteal' (pa-ROSS-tee-al) or 'periosteal' (peh-RIH -oss-TEE-al) osteosarcoma.'
Very rarely tumours, which appear identical to osteosarcoma, can arise outside of the bone in unusual places. This is known as 'extraosseous (extra-OSSY-os) osteosarcoma.'
Last reviewed: October 2010; Version: 1.1
Review due: October 2011
The authors and reviewers of this information are committed to producing reliable, accurate and up to date content reflecting the best available research evidence, and best clinical practice. We aim to provide unbiased information free from any commercial conflicts of interest. This article is for information only and should not be used for the diagnosis or treatment of medical conditions. BCRT can answer questions about primary bone cancers, including treatments and research but we are unable to offer specific advice about individual patients. If you are worried about any symptoms please consult your doctor.
