Metastatic cancer

Metastatic cancer is cancer that has spread from the part of the body where it started (called its primary site) to other parts of the body. When cells break away from a cancerous tumor, they can travel to other areas of the body through the bloodstream or through the lymph system. Most often, cancer cells that break off enter the bloodstream. From there they can end up in any organ or tissue.

Cancer cells can also travel through the lymph system. This system includes lymph nodes and lymph vessels. The lymph vessels are much like blood vessels, except they carry a clear fluid called lymph back to the heart. Cancer cells that travel through the lymph system often end up in the lymph nodes, but they can also spread to other organs.

Many of the cancer cells that break off from the original tumor die without causing any problems. Some, however, settle in a new area. There, they begin to grow and form new tumors. This spread of cancer to a new part of the body is called metastasis. When cancer spreads, we say that it metastasizes. If there is only a single tumor, it is called a metastasis or a metastatic tumor. When there are 2 or more metastatic tumors, we call them metastases.

Even when cancer has spread from one part of the body to another, it is still named after the part of the body where it started. For example, if prostate cancer spreads to the bones, it is still called prostate cancer, not bone cancer. If breast cancer spreads to the lungs it is still breast cancer, not lung cancer. A person with breast cancer that has spread to 2 or more bones is said to have "breast cancer with bone metastases."

Sometimes metastatic tumors are found by tests that are done when the primary cancer is first diagnosed. In other cases, the metastasis is found first, causing the doctor to look for the place that the cancer started. Usually the primary tumor is found, but sometimes even though a cancer that has spread widely throughout the body, doctors are unable to find where it started. When doctors can't figure out where the primary cancer site is, it is called cancer of unknown primary. This is discussed further in a separate American Cancer Society document called Cancer of Unknown Primary.

Sometimes, no metastases are seen when the cancer is first found. Instead, they are found later, after the patient has been treated and was thought to be cancer free. When a cancer has come back after treatment, it is called recurrence. When it comes back as metastases, it is called a distant recurrence. In order for a cancer to recur as metastatic disease, some cancer cells had to have broken off from the primary tumor before treatment was complete. These cells traveled through the body, and started growing in new places. Different cancers tend to spread to different sites, but the most common sites of distant recurrence include the bones, the liver, and the lungs.

What does it mean when you have bone metastases?

Cancer cells that break off from a primary tumor and enter the bloodstream can reach nearly all tissues of the body. Bones are a common place for these cancer cells to settle in and start growing.

Cancers that start in the bone are called primary bone cancers. Bone metastasis and primary bone cancers are very different. Primary bone cancer is much rarer than bone metastasis. If you would like information on primary bone cancers, see our documents Bone Cancer, Osteosarcoma, Multiple Myeloma, and Ewing Family of Tumors.

Bone metastasis is one of the most frequent causes of pain in people with cancer. When a cancer spreads to the bone, it can make the bones weaker and even cause them to break. As the cancer cells damage the bones, calcium is released. This can lead to problems from high blood calcium levels. Bone metastasis also causes other problems that can limit your ability to keep up your usual activities and lifestyle.

Bone metastases will develop in many people with cancer at some point in the course of their disease. Bones are often a site for metastases for certain common tumors, such as breast and prostate cancers.

Metastases can occur in any bone in the body, but are most often found in bones near the center of the body. The spine is the most common site of bone metastasis. The next most common parts are the pelvis (hip), upper leg bone (femur), upper arm bone (humerus), ribs, and the skull.

Bone metastasis can only develop if you already have cancer somewhere else. Once cancer has spread to several sites in the body it is rarely able to be cured, but often it can still be treated. Even if cure is no longer possible, treating the cancer may be able to help you live longer and feel better. Other types of treatment can help prevent or manage cancer symptoms. (See the section, "How are bone metastases treated?")

Last Medical Review: 01/13/2008
Last Revised: 05/13/2009