Bone metastases are tumors that occur when cancer cells break away from the place where they first started growing and move into bone tissue. Bone metastases are considered a form of advanced cancer. These secondary cancers within the bone are difficult to completely cure, but can be treated to lessen symptoms and lengthen life.
Bone metastases are not bone cancer. Bone metastases are formed from cancerous cells that start somewhere else in the body. So, bone metastases could, for instance, be cancerous breast tissue, or another type of tissue elsewhere in the body, that has started growing inside bone tissue.
Cancer is a disease in which abnormal cells start dividing without control. Some tumors can have cells break off and move around the body. Most of these shed cells die off, but some live on in new tissue and create a metastatic tumor. These metastases can remain hidden, even when the original tumor is gone and the patient is pronounced cancer-free.
It is unclear why certain tumors become metastatic, and others do not. In certain types of cancer, such as advanced breast cancer or advanced prostate cancer, up to 70 percent of patients develop bone metastases (Roodman, 2004).
The most common cancers that result in bone metastases include:
- breast cancer
- prostate cancer
- lung cancer
- kidney cancer
- thyroid cancer
The most common (but not only) locations for bone metastases include:
- pelvis (hips)
- long bones of the leg
- upper arms
Bone metastases are common in many cancer patients. Unfortunately, bone metastases can result in severe pain and neurological impairment due to changes in bone structure. Other symptoms of bone metastases can include:
- fragile bones
- high levels of calcium in the blood (which may cause nausea, confusion)
- loss of urinary or bowel control
- weakness in the legs
- anemia due to the loss of bone marrow
Bones can be severely damaged by metastatic cancer. Metastatic tumors can destroy surrounding bone tissue, causing “osteolytic bone destruction.” Osteolytic damage occurs most often from tumors that originate in the colon, kidney, lung or thyroid. Other damage can result when new bone is formed due to chemicals released by the tumor, and this new bone may be weak and deformed. This is osteoblastic (bone formation) damage, and is seen in cancers that start life as prostate, bladder, or stomach cells. Some cancers, like breast cancer, can create both osteolytic and osteoblastic damage.
Both osteoblastic and osteolytic damage can result in “pathological” bone fractures. These bones break not from a fall or pressure, but during everyday activities. Bone damage in the bones of the spine can also affect the nerves of the spinal cord, causing neurological problems.
After a full medical history and physical exam, including a discussion of any past incidence of cancer, tests will be performed. X-rays will be taken of the affected bone. Bone scans may be ordered to examine more bones to see if they are affected. Computed tomography (CT) scans and magnetic resonance imaging (MRI) may be done in some cases. Blood tests may also be done. If there is some question as to whether the affected bone is the result of a bone metastasis or a primary bone cancer, a biopsy may be performed, in which a small amount of the tumor is removed and thoroughly examined by a pathologist.
Treatment of metastases often depends on the location and the source tumor cells. Treatments can include radiation, medication, and surgery.
Radiation therapy is often used to slow the growth of a bone metastasis. There are multiple types of radiation therapy, including:
- Local field radiation: This is directed at tumor and nearby tissue, and can result in complete pain relief in 50-60 percent of cases (University of Connecticut).
- Hemi-body radiation: This is directed at a large part of the body, and is used if there are multiple bone metastases.
- Radioisotope therapy: This involves injection of radioactive medication through a vein.
Medications are a key part of therapy for patients with bone metastases, and may include one or more of the following:
- bone-building medications (bisphosphonates help reduce bone damage)
- chemotherapy to kill tumor cells and reduce tumor size
- hormone therapy (certain cancers like breast cancer and prostate cancer may be slowed by certain hormones)
- pain medications
Surgery may be necessary when bones have fractured or will soon fracture. Tumors may be removed during surgery. Fixation devices may be attached directly to surrounding bone. Bone cement may be used for reinforcing bone structure.
Heating or freezing cancer cells with a probe (radiofrequency ablation or cryoablation) can also reduce tumor size.
All of these treatment methods have complications and risks. Each patient will have a unique treatment for their specific cancer and work with a variety of doctors to tailor their care.
Bone metastases occur in advanced cancer. Often it is not possible for all cancer cells to be removed and the patient declared cancer-free. Treatments available may reduce the size and slow the growth of metastases so that pain and other symptoms can be reduced, and a patient can live longer.