A bone tumor is an abnormal growth of cells within the bone that may be noncancerous (benign) or cancerous (malignant).

The cause of bone tumors is unknown. They often arise in areas of rapid growth. Possible causes include:

• Inherited genetic mutations
• Radiation
• Trauma

But in most cases no specific cause is found.

Osteochondromas are the most common noncancerous (benign) bone tumors, and occur most often in people between the ages of 10 and 20. Some benign bone tumors go away on their own and do not require treatment. These benign tumors are monitored periodically by x-ray.

Cancers that start in the bones are referred to as primary bone tumors. Cancers that start in another part of the body (such as the breast, lungs, or colon) are not considered bone tumors. Multiple myeloma often affects or involves the bone, but is not considered a bone tumor.

Cancerous (malignant) bone tumors include:

• Chondrosarcoma
• Ewing's sarcoma
• Fibrosarcoma
• Osteosarcomas

The most common cancers that spread to the bone are cancer of the:

• Breast
• Kidney
• Lung
• Prostate
• Thyroid

These forms of cancer usually affect older people.

Bone cancer was once very common among people who painted radium on watch faces (to produce glow-in-the-dark dials). The painters would "tip" the brush with their tongue (in order to produce fine work) and absorb minute amounts of radium, which deposited in the bone and caused cancer. The practice of using radium paint was abandoned in the middle of the 20th century.

The incidence of bone cancer is higher in families with familial cancer syndromes. The incidence of bone cancer in children is approximately 5 cases per million children each year.