Bone metastases are a common complication of lung cancer. Others cancers that metastasize to bone include multiple myeloma, breast, prostate, kidney, and thyroid cancer.

Metastases are cancer cells that have spread from their site of origin to another location in the body. Cancer cells can spread, or metastasize, through the blood and lymph systems. A cancer cell may break away from the original location in the body and travel in one of these systems until it gets lodged in a small vessel in another area of the body. Once there, the cell grows and divides, thereby establishing cancer in that new tissue.

Metastases are not new or different cancers; the cancer cells in the new location are the same as the original cancer, only in a different location.

Bone is one of the most common locations in the body to which cancer metastasizes. Bone metastases usually occur by way of the blood stream. Cancer may also spread to bone by erosion from the adjacent cancer, though this occurs less frequently than spread by the blood stream.

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 up 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).

The damage caused by bone metastases may make the bone more susceptible to complications such as pain or fractures. Another more serious complication of bone metastases is the risk of hypercalcemia. Hypercalcemia is an increased level of calcium in the blood and can be a medical emergency.

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 are the back, pelvis, upper leg, ribs, upper arm, and skull. More than 90% of all metastases are found in these locations.