Cancer that begins in an organ, such as the lungs, breast, or prostate, and then spreads to bone is called metastatic bone disease (MBD). More than 1.2 million new cancer cases are diagnosed each year. Approximately 50% of these tumors can spread (metastasize) to the skeleton.
With improved medical treatment of many cancers — especially breast, lung, and prostate — patients are living longer. However, the primary cancers in more of these patients are spreading to bone. The tumors that result are called bone metastases.
Every cancer patient should discuss his or her risk for developing MBD with an oncologist. Some cancers do not readily spread to bone, while others do.
The most common cancers that arise from organs and spread to bone include:
MBD causes pain in the area of spread, damages and weakens bone, and puts the patient at a greater risk for broken bones. It can make it hard to participate in daily activities. The biggest concern for patients with MBD is the general loss in quality of life.
How much of an effect MBD has on a patient will vary and is associated with how much the cancer has spread, which bones are affected, and how severe the bone damage is. There are a range of treatment options, however, that can help patients manage pain and maintain their independence and activity levels.
After the lung and the liver, the skeleton is the most common site of spread of cancers that begin in organs. Metastases to the lung and liver are often not detected until late in the course of disease because patients experience no symptoms. In contrast, bone metastases are generally painful when they occur.
Cancer most commonly spreads to these sites in the skeleton:
- Upper arm
- Long bones of the leg
Sometimes, the tumor can completely destroy the bone in a particular area. This type of process is termed osteolytic bone destruction. This type of damage is most common in cancers that have spread to bone from the lung, thyroid, kidney, and colon.
Alternatively, new bone can form in response to the cancer spread. This new bone, called osteoblastic, grows abnormally and causes the bone to be weak and deformed. It is more frequently seen in spread of prostate, bladder, and stomach cancer.
Breast cancer often behaves in a mixed osteolytic and osteoblastic manner. Osteolytic and osteoblastic metastatic bone disease occurs because the different cancer cells secrete factors that interact with the naturally occurring cells in the bone and cause bone destruction, new bone formation, or both.
Because MBD weakens the affected bones, people with the disease are prone to fractures. Broken bones caused by MBD are termed "pathological fractures."
Sometimes the bone has not yet broken but is so weak that a break is imminent. Such scenarios are termed "impending pathologic fractures." Patients with impending or actual fractures may be forced to remain on bedrest for long periods of time, which can lead to possible chemical imbalances in the blood such as increased calcium levels (hypercalcemia).
Patients with cancer that has spread to the spinal bones may develop nerve damage that can lead to paralysis or loss of the use of the legs and/or arms.
- Pain. The most common symptom of MBD is pain. Patients may have pain in the spine, pelvis, or extremities because the bone has been weakened by the tumor.
- Fractures. Weakened bones break more easily. A fracture from a minor injury is another possible sign of MBD.
- Anemia. The most common sites of spread — spine, pelvis, ribs, skull, upper arm, and long bones of the leg — correspond to areas of bone marrow that produce high levels of red blood cells, the cells responsible for carrying oxygen to tissues in the body. Anemia (decreased red blood cell production) is a common blood abnormality in patients with MBD.
A cancer patient who experiences any pain, especially in the back, legs, and arms, should notify his or her doctor immediately. Pain that occurs without activity (i.e., walking or lifting an object) is particularly concerning.
Medical History and Physical Examination
It is important for your doctor to understand your medical condition and your symptoms. Your doctor will ask questions about the nature of any pain you are having, your current health, and past medical conditions. The information your doctor learns is called your medical history.
After the medical history, your doctor will perform a physical examination, concentrating on the painful areas.
X-rays. After the interview and physical examination, your doctor will order x-rays if he or she suspects that you have metastatic bone disease. Because some pain is referred from other areas (for example, knee pain may be arising in the hip), your doctor may order x-rays of bone beyond the areas where you are experiencing discomfort.
This x-ray of the upper arm shows a pathological fracture in the humerus (arrow).
The x-ray examination can tell an oncologist a great deal of information about whether and how much of the bone is involved.
Other imaging tests. Your doctor may also order a bone scan. This test is helpful in determining if other bones, in addition to the one in question, are involved with metastatic bone disease. In select cases, a computerized tomography (CT) scan and/or magnetic resonance image (MRI) may be ordered, especially in cases where the spine or pelvis may be involved.
A technetium bone scan demonstrates extensive bony metastasis throughout the skeleton (arrows).
MBD vs. Primary Bone Cancer
The diagnosis of metastatic bone disease should not be assumed unless a patient has a known primary