What are Bone Metastases?

Bone metastases are tumors that develop from cancer cells that began in another part of the body but broke away from that tumor and spread to the bone. Metastasis is the movement of disease from one body part or organ to another more distant area of the body. Cancer is a disease that can metastasize from the primary site to the bones and grow into a new tumor. A single new tumor is called metastasis or a metastatic tumor. "Metastases" is the term given to two or more new tumors.

Cancer usually starts in a particular part of the body. This area is called the primary site. Cancer cells can break off from the primary site and be carried by the blood or lymph through the body. Most cancer cells that split away die without causing more disease. The cells that do not die can settle in new areas of the body and grow into new tumors.

Cancer type is identified by the name of the primary site, no matter what other parts of the body it has spread to. If the primary site is the lungs and it has metastasized to the skeletal system, it is called “lung cancer with bone metastases." Cancer that is most likely to spread to the bone has the breast, kidney, lung, prostate or thyroid as its primary site.

Bone metastases happen when one or more cancer cells split off from the primary site. These cells are carried through the bloodstream to the bone marrow. Here they settle, grow and form a bone tumor. Bone pain usually is the first symptom that occurs when cancer has spread to the skeletal system.

Metastases to the bones weaken them and can cause them to break. They also can cause compression fractures in the spine. Bone metastases cause pain because the tumors stretch the periosteum, the membrane that lines the outer surface of the bones, and stimulate the nerves. Metastases in the bone can cause reduced mobility and limit the quality of life and longevity.

Bones in the center of the body are the most prone to metastases. The spine is affected the most often. Bone metastases also are commonly found on the skull, humerus, ribs, pelvis and femur. The extremities rarely are affected.

It is difficult to identify early stages of bone metastases by using an X-ray. If tumors do show on the film, it is difficult to distinguish whether they are benign or malignant. A magnetic resonance imaging (MRI) exam is the best method of detecting and identifying cancerous bone tumors.

Bone metastasis is treated with systemic therapies that destroy the cancer or slow its growth. Systemic therapies carry cancer-fighting agents through the bloodstream to the cancer site. Chemotherapy is one such therapy used in treating bone cancer. Radiation therapy is a localized treatment that destroys cancer in specific areas. It is used as a pain-relieving measure when treating metastatic tumors.