Overview

The spread of cancer from its site of origin to another location in the body is called metastasis. Cancer cells can spread, or metastasize, through the blood and lymph systems. Bone metastases usually occur by way of the bloodstream. A cancer cell may break away from the original location in the body and travel in the circulatory system until it gets lodged in a small capillary network in bone tissue. Cancer may also spread to bone by erosion from the adjacent cancer, though this occurs less frequently than spread by the bloodstream.Bone is one of the most common locations in the body to which cancer metastasizes. The major cancer types that tend to metastasize to bone include multiple myeloma, breast, prostate, lung, kidney, and thyroid cancers. Bone metastases may cause pain, may make the bones more susceptible to fractures, and may cause increased levels of calcium in the blood.Bone metastases result in lesions or injury to the bone tissue. There are two types of lesions: lytic lesions, which destroy bone material; and blastic lesions, which fill the bone with extra cells. Normal bone is constantly being remodeled, or broken down and rebuilt. Cancer cells that have spread to the bone disrupt the balance between the activity of osteoclasts (cells that break down bone) and osteoblasts (cells that build bone).Bone metastases generally occur in the central parts of the skeleton, although they may be found anywhere in the skeletal system. Common sites for bone metastases include the back, pelvis, upper leg, ribs, upper arm, and skull. More than 90% of all metastases are found in these locations.

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