An Overview of Bone Metastases

Bone metastases are common in people who've had cancer, especially that of the breast, lung, or prostate. They occur when cells from the original tumor break off and take up residence in the bone. Metastases are very painful and are different from tumors that originate in the bone. For example, breast cancer that moves to the bones is not bone cancer, but rather breast cancer metastatic to bone.

Common Sites

Each type of cancer has a tendency to spread to certain bones in the body more often than others, but this can vary. Metastases have occurred to nearly every bone in the body.

It's typical for bone metastases to occur in a few different bones at the same time, such as the spine and the pelvis. Metastases may also occur in other regions of the body (such as the liver, lungs, or brain) at the same time as the bones.

Symptoms and Complications

Bone metastases can lead to many different symptoms and complications, some of which may lead to the discovery that cancer has recurred. Many of them may require treatment above and beyond what's needed to battle the tumor(s).

• Difficult-to-manage pain
• Fractures and fracture risk
• Spinal cord compression
• Loss of mobility
• Hypercalcemia

Hypercalcemia

In hypercalcemia, bones release calcium into the blood as they're broken down by cancer. While calcium is something your body needs, having too much leads to several problems. Symptoms include:

• Constipation
• Fatigue
• Extreme thirst
• Muscle weakness

In severe cases, untreated hypercalcemia can lead to:

• Kidney failure
• Coma
• Death

Get treatment right away if you have symptoms that suggest hypercalcemia.

Causes

Experts don't yet understand why cancer spreads to bones. The bones are rich with blood vessels, but so are the liver and lungs—areas to which cancer spreads less frequently than bone. Metastases are the cause of death in 90% of fatal breast cancer cases, so this area is being actively investigated.

One theory is that cancer may lie dormant in bone marrow since the bones that cancer most commonly spreads to are those that are rich in bone marrow. This may explain why cancer can hide in the body for years, or even decades, and then recur.

Diagnosis

Bone metastases from breast cancer may be diagnosed in a number of different ways. Sometimes metastases are seen when an X-ray is done for a fracture that occurred with minimal trauma due to the weakening of a bone (what's known as a pathologic fracture).

Other times, they're diagnosed incidentally when a test such as a positron emission tomography (PET) scan is done for another reason.

Tests done specifically to look for bone metastases include:

• Bone scans
• PET scans
• Computed tomography (CT) scans
• Single-photon emission computerized tomography (SPECT) scans
• Whole-body magnetic resonance imaging (MRI)

The types of scans your healthcare provider orders will depend on a variety of factors, and some scans may be done in combination to reach a diagnosis. There's no consensus that one test or combination of tests is best in all cases.

Treatment

Addressing bone issues and bone metastases are important no matter what stage of cancer a person has. Cancer treatments such as hormonal therapies can lead to bone loss. In fact, medications used for bone metastases (bisphosphonates) are now being considered even for those with early-stage breast cancer as a way to strengthen bones and possibly prevent bone metastases from occurring in the first place.

A number of different treatments are available for bone metastases. The option that is best for you depends on a number of factors, such as the number and location of bones affected, the presence of other metastases, and your general health.

General cancer treatments such as chemotherapy, hormonal therapies, and targeted medications are often used, as are treatments designed specifically to slow the spread of cancer to bones. They frequently result in the successful management of cancer for quite some time.

Radiation Therapy

Radiation therapy is a common choice. It can help both to decrease pain and reduce the risk of fractures, often being the most effective treatment for alleviating pain. Radiation is a "local treatment," which means that it works better for isolated areas of metastases than those that are widespread. Even so, when combined with immunotherapy drugs, some people experience what's referred to as the abscopal effect, in which radiation appears to prime the immune system. This results in a decrease in the tumor at sites distant from where the radiation was given.

In the past, radiation was often given over several sessions, but a 2019 study suggests that a single dose is not only easier from a quality-of-life standpoint (fewer visits), but may more effectively reduce pain and reduce the risk of cancer recurring at the site—and with no greater side effects. In this approach, a single dose (either 12 Gy or 16 Gy, depending on the size of the metastasis) given by a specialized type of radiation called stereotactic body radiotherapy (SBRT) was even more effective than 10 sessions delivering a total of 30 Gy of radiation.

Radiopharmaceuticals

Radiopharmaceuticals are medications that include a particle of radiation attached to another chemical, which is injected into the bloodstream. The radiation is thus delivered directly to the bone metastases. Examples of these drugs include Strontium-89 and Radium-223.

Radiopharmaceuticals may be particularly helpful for those who have multiple or extensive bone metastases that would be difficult to treat with local therapies such as radiation therapy. These medications have relatively few side effects and can be very effective in controlling bone pain.

Bone-Modifying Agents

Bone-modifying agents are drugs that can be used orally or by injection to reduce bone metastases. These include:

• Bisphosphonates: First approved for osteoporosis, these drugs were later then found to be effective in treating and preventing bone metastases. They also appear to have strong anti-tumor effects and help prevent bone loss due to hormonal therapies (such as aromatase inhibitors). An example is Zometa (zoledronic acid). These medications are being considered for treating early-stage breast cancer in women on ovarian suppression therapy. Bisphosphonates do carry a rare side effect of osteonecrosis of the jaw.
• Xgeva (denosumab): Denosumab is an antibody that has been found to be effective in reducing complications such as fractures for people with bone metastases. It also appears to have anti-cancer properties. It is given as a subcutaneous injection once every four weeks.

Treatment for Complications

While the following will not address the metastasized cancer itself, they can help patients with issues that stem from such disease.

• Pain control: Metastases to bones can be very painful, but you have a lot of options for pain relief. Finding the right medications and balancing the side effects with effectiveness can be challenging. If you're struggling to find that balance, you may want to work with a palliative care healthcare provider or pain specialist. They use numerous therapies in addition to medications, including nerve blocks.
• Fractures and fracture risk: Surgery is used most often to stabilize fractures or areas of bone at risk for fractures. (It may also be done to remove tumors putting significant pressure on the spinal cord.) When fractures are in the long bones of the arms or legs, a rod is usually placed to provide support for a weakened bone. Vertebroplasty or "cement" may be used for spinal fractures or weakened areas where fractures are likely to occur.
• Hypercalcemia: First-line treatment includes IV rehydration and bisphosphonates. Sometimes other medications, such as calcitonin, gallium nitrate, or mithramycin may be used. If hypercalcemia is severe, dialysis is another option.

Prognosis

The prognosis for bone metastases depends on what type of cancer it is.

For example, the average overall survival for metastatic breast cancer with bone metastases is 19 to 25 months (and thought to be increasing), with around 20% of people surviving beyond five years. In bone metastases from lung cancer, the median survival time is just six to seven months.

A Word From Verywell

While bone metastases confirm that your cancer has spread and can be painful, there are some excellent treatment options available, with more treatments currently being evaluated in clinical trials. After you have adjusted to this diagnosis, work with your healthcare team to find the best regimen to control your disease and ease symptoms. Take it one day at a time.