Bone cancer is the growth of abnormal cells in the bone. These cells form a tumor. A cancerous (malignant) tumor can grow and spread to other parts of the body. (A benign bone tumor is not cancer.)

A malignant bone tumor that starts in the bones is called primary bone cancer. A bone tumor that started in another part of the body and spread (metastasized) to the bones is called secondary bone cancer, bone metastasis, or metastatic cancer. (For example, a bone tumor caused by the spread of lung cancer is called metastatic lung cancer.)

Most primary bone cancers are a type of cancer called sarcoma. Examples include osteosarcoma, Ewing sarcoma, and chondrosarcoma.