Primary bone cancer is different from secondary or metastatic bone cancer. In secondary or metastatic bone cancer, the cancer originates in a different place but spreads (metastasizes) to the bones. For example, someone with prostate cancer may develop bone lesions from the prostate cancer. But, even though the cancer has spread to the bone, it's still prostate cancer.
Metastatic bone cancer is much more common than is primary bone cancer. Additionally, primary bone cancer doesn't refer to cancer that begins in the bone marrow — the soft inner core of your bones that makes your blood cells. Bone marrow cancers include diseases such as multiple myeloma and acute and chronic leukemias.
In general, no one knows for certain what causes most primary bone cancers. Adults with Paget's disease of bone, which involves abnormal development of new bone cells, may be at increased risk of osteosarcoma.

In a few cases, bone cancers may have a hereditary component, such as in:
Li-Fraumeni syndrome. This condition is characterized by an increased risk of many different cancers, including osteosarcoma, breast cancer, brain cancer and others.
Rothmund-Thomson syndrome. This condition causes short stature, skeletal problems and rashes, and increases risk of bone cancer.
Hereditary retinoblastoma. Children with this rare cancer of the eye have an increased risk of osteosarcoma.
Multiple exostoses. Children with this inherited condition that causes cartilage bumps to form on your bones have an increased risk of chondrosarcoma.
The association with radiation Radiation is occasionally associated with bone cancer. Exposure to radiation from a diagnostic X-ray won't harm you. But heavy doses of radiation, such as radiation therapy given for other cancers, can increase your risk of developing bone cancer, especially if you receive the therapy at a young age.
Still, radiation therapy is becoming more and more sophisticated, which may lead to fewer of such side effects. For example, doctors today are better able to regulate doses of radiation and more precisely target the tumor being treated.