What is osteosarcoma?
This information has been written for patients, their families and friends, and the general public to help them understand more about chondrosarcoma: what it is and the different types. This information is produced in accordance with BCRT's information policy.
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 bone in a tumour sample under the microscope, this helps to confirm a diagnosis of osteosarcoma.
The majority of osteosarcomas arise from a single place within the area of a long bone known as the metaphysis (meta-FEE-siss). The metaphysis contains the area of the bone where cells are growing and dividing, this is called the epiphyseal (epi-FEE-see-al) plate.
The long bones of the skeleton are those bones that are very much longer than they are wide. The best examples being the bones of the limbs, for example, the thigh bone (femur) or the upper arm bone (humerus). Figure 1 shows what is inside a long bone, and where osteosarcoma can arise.
Figure 1: What is inside a bone?
(Image by Hannah Thompson)
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, these are shown in figure 2. Tumours found in the bones of the face, skull and spine are more common in older osteosarcoma patients than younger osteosarcoma patients.
Figure 2: Where in the skeleton does osteosarcoma most often occur?
(Image by Hannah Thompson)
Very rarely, osteosarcoma can start in more than one bone at the same time; this is called multi-focal osteosarcoma.
Osteosarcoma behaves in an aggressive manner, which means it can spread in the bloodstream from or through the bone and into 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 can spread to other parts of the body quickly, patients need treatment to the whole body; this is called systemic treatment.
When looked at under the microscope, all osteosarcomas can be seen to consist of abnormal cells that are 'trying' to make bone. By looking closely at what kind of cells are in the tumour, doctors can class each patient’s osteosarcoma as one of 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 all five are 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, meaning that the cancer cells can invade surrounding healthy tissues and spread to other organs. As a result, the cells can spread to other sites in the body at an early disease 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.
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.' These are treated in the same way as conventional osteosarcoma; with a combination of surgery and chemotherapy if the tumour is of a high grade.
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.
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Version 2 produced January 2013
Information will be reviewed in January 2015