When cancer cells spread from one area of the body to your bones, it is called bone metastasis (or bone mets). Cancer that metastasizes (spreads) to the bone is not bone cancer. It is cancer of where the primary (original) tumor is. Cancer cells from the primary tumor can travel through the bloodstream or lymph system to a part of a bone.
Bone mets, sometimes called lesions, can be a part of advanced cancer and can happen in any bone in the body. They tend to happen more often in bones in the middle of the body, like the spine. Other common sites for bone mets are the pelvis (hip), upper leg bone (femur), upper arm bone (humerus), ribs, and the skull. The most common cancers to metastasize to the bone are breast, prostate, lung, thyroid, and kidney cancer.
What are the types of bone metastasis?
When metastatic cancer cells reach the bones, they release substances that turn on osteoclasts or osteoblasts. They make up the two types of bone mets:
- The tumor has caused the bones to break down or thin.
- Calcium is released from the bone into the bloodstream.
- On X-rays, the mets are seen as holes, called "lucencies.”
- Often seen in multiple myeloma but may be seen in patients with other types of cancers.
- Increased bone production.
- Your tumor sends signals to the bone to make extra bone cells. This causes rigid (stiff), thickened, inflexible bone to form.
- Most often seen in prostate cancer.
Cancers can lead to osteolytic or osteoblastic bony changes or both.
Why does cancer spread to the bone?
There are three reasons cancer spreads to the bone:
- Blood Flow: There is a lot of blood flow to the bone and bone marrow. Once cancer cells get into the blood vessels, they can travel all over the body. They often go where there is the highest flow of blood.
- Adhesive Molecules: Tumor cells put out adhesive (sticky) molecules that can stick to the bone marrow and bone. This can cause the tumor to signal for more bone to be destroyed and for more tumor to grow within the bone.
- Growth Factors: The bone has a lot of growth factors. These growth factors signal cells to divide, grow, and mature. As the cancer attacks the bone, these growth factors are released and cause tumor cells to grow.
What are the signs of bone metastasis?
The most common signs of bone metastases are:
- Bone pain: Often the first symptom. The pain often comes and goes, is worse at night, and is often relieved with movement. It may worsen and become constant.
- Fracture (broken bone): Bone may weaken and fracture (break). Fractures from bone metastases are called "pathologic" fractures. The fractures could be caused by trauma, but if the bone is weak enough, it can break just by doing an everyday activity.
- Spinal cord compression: Cancer that has spread to the spine can cause pressure on the spinal cord called spinal cord compression. Signs are new or worsening pain in the back or neck, numbness and weakness in the body below the tumor, and trouble walking. Spinal cord compression can lead to nerve damage and even paralysis (losing the ability to move). *Spinal cord compression is an oncologic emergency, which is a serious health problem. Oncologic emergencies need to be treated right away.
- Bowel and bladder problems: You may lose control of urine and/or stool (continence) or have severe constipation and urinary retention (not being able to pee or not emptying your bladder fully).
- High calcium levels: Some bone metastases can cause calcium to leak from the bones into the bloodstream. This can lead to high calcium levels (hypercalcemia) in the blood. Hypercalcemia can cause constipation, nausea, loss of appetite, extreme thirst, frequent urination, dehydration, fatigue, and in very serious cases, confusion and even coma.
Your provider will watch you closely during the treatment of your primary cancer for these signs and symptoms. You should tell your provider if you start to have any symptoms of bone metastases.
How are bone metastases diagnosed?
If you have signs of bone metastasis, tests can be done to find the cause. In some cases, bone metastasis may be found before the symptoms start. X-rays, bone scans, and MRIs, among other tests, are used to diagnose bone metastases.
- Bone metastases often do not show up on plain x-rays until they are quite advanced. X-rays are good at finding osteolytic lesions. These often look like "holes" or dark spots in the bone on the x-ray film.
- A bone scan can find very early bone metastases. A small amount of radio-tracing material is injected into a vein. Special x-rays are taken a short time after the injection. The radiotracer will go to the site of the metastases, which will look darker and denser on the film. Infections, arthritis, and old fractures can also show as dark spots on the bone scan and may at first look like cancer. Bone scans are also used to follow patients with known bone metastasis.
- CT scan images can show if a cancer has spread to the bone.
- An MRI is useful when looking at nerve roots that are being pressed on by tumor or bone pieces (called spinal cord compression).
- There are no specific blood tests that are used to diagnose bone metastasis. There are blood tests that may suggest bone lesions, but the diagnosis comes from radiology testing, symptoms, and the type of cancer. For example, high levels of calcium can be related to bone metastasis, but these lab tests alone cannot make a diagnosis. An elevated tumor marker level may also suggest that cancer has metastasized to the bone.
- A biopsy may be done to test the lesion for cancer cells. During a biopsy, a piece or all of the lesion is removed. It is looked at under a microscope by a pathologist to see what type of cells make up the tumor. The type of biopsy used depends on where the tumor is found.
If you are diagnosed with bone mets, your team will talk to you about possible treatment and management.
How are bone mets treated?
Treating bone mets is important because it can improve symptoms and your quality of life. Often, treatment of your primary cancer is the best treatment for bone metastasis. There are also treatments used to treat bone mets. These treatments are either systemic (affect your whole body) or local (affect a specific area). Clinical trials, physical therapy, and pain management may also be used to manage bone mets.
Systemic treatments get into the bloodstream and go throughout the whole body to kill cancer cells. They can be given by mouth (orally) or directly into a vein (IV). Systemic treatments are:
- Medication: Chemotherapy, targeted therapy, immunotherapy, and hormone therapy treat the primary cancer and can go through the body to kill cancer cells, including bone met cells. Bisphosphonates can help make diseased bone stronger and prevent fractures. Denosumab is a targeted therapy that can prevent further bone damage from cancer cells.
- Radionuclide Therapy: A radioactive element is injected into the body and goes inside the bone mets. The radiation kills the cancer cells and lessens pain.
Local therapies target only the bone met and not the whole body:
- Radiation Therapy: Radiation is the use of high-energy x-rays to destroy cancer cells. It can be directed at bone mets.
- Ablation: Radiofrequency (electric current) or cryoablation (cold) uses a needle placed directly into a tumor to destroy cancer cells.
- Bone Cement: Used to treat fractures caused by bone mets. Bone cement strengthens or stabilizes the bone.
- Surgery: Rods, screws, pins, plates, and cages may be used to stabilize, treat, and prevent fractures.
More information about the treatment of bone mets can be found in “Bone Metastases Treatment”.
Research is ongoing in the prevention and treatment of bone metastases. Your care team will monitor you for bone mets throughout your cancer treatments. If you have bone mets, talk with your provider about your treatment options and how to best manage your mets.
The American Cancer Society. Advanced Cancer, Metastatic Cancer, and Bone Metastasis. Treating Bone Metastases. Found at: https://www.cancer.org/treatment/understanding-your-diagnosis/advanced-cancer/treating-bone-metastases.html
Radiation Therapy Answers. Bone Metastases. Found at: http://www.rtanswers.org/bonemetastases/