When Breast Cancer Spreads to the Bones

Management of Bone Metastases from Breast Cancer

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Breast cancer spreads to the bones far too often. Bone metastases occur in roughly 70 percent of women with metastatic breast cancer (stage 4 breast cancer) and are often the first sign that a cancer has recurred. Thankfully, bone metastases may have a better prognosis than that of breast cancer which has spread to other regions, and several treatments are available which not only reduce pain but may improve survival as well.

Let's take a look at which bones breast cancer most commonly spreads to, the symptoms of bone metastases, the different treatment options available, and possible complications you should be familiar with.

Breast Cancer with Bone Metastases

Breast cancer which spreads to the bone is a source of much confusion, so we will start by defining exactly what this means. Breast cancer which spreads (metastasizes) to bone is still breast cancer. If you took a sample of the tumor in a bone and looked at it under the microscope, you would see cancerous breast cells.

Breast cancer which has spread to the bones is not bone cancer (under a microscope bone cancer would reveal cancerous bone cells). When breast cancer spreads to bones the correct terminology is "breast cancer metastatic to bones." When cancer is found in bones it is much more likely to be metastatic cancer from another area of the body than primary bone cancer.

Importance of Bone Metastases

Addressing bone issues and bone metastases is important no matter what stage of breast cancer a person has. Not only may breast cancer spread to bones, but treatments for breast cancer 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.

The pain which often accompanies bone metastases, combined with a decrease in mobility due to fractures or a predisposition to fractures, can have a significant impact on quality of life for women living with metastatic breast cancer. Yet, unlike the common perception that there is little you can do if you have stage 4 breast cancer, there is much that can be done to not only reduce the pain and complications of bone metastases, but to extend life.

Breast Cancer Spread to the Bone - Overview

As noted above, bone metastases from breast cancer are the most common site of distant metastases with breast cancer. Bone metastases are slightly more common in women who have estrogen receptor positive breast cancer (liver and brain metastases are more common in women with HER2/neu positive and triple negative breast cancer).

Bone metastases are also more common in women with invasive ductal breast cancer than invasive lobular breast cancer (in lobular carcinoma, metastases to the abdomen (peritoneal metastases) are more common). Of the different subtypes of breast cancer, bone metastases are more common in luminal cancers.

What Bones Does Breast Cancer Spread To?

Breast cancer has a tendency to spread to some bones in the body more often than others, but this can vary and metastases have occurred to nearly every bone in the body.

Metastases occur most commonly to the:

  • Spine
  • Ribs
  • Pelvis
  • Long bones of the arms and legs (the humerus and the femur)

It's not uncommon 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 they are noted in bones.

Why Does Breast Cancer Spread to Bones?

We don't currently understand why breast cancer spreads to bones. The bones are rich with blood vessels, but so are the liver and lung, areas to which breast cancer spreads but with a lower frequency than bone.

Since metastases are so important (metastases are the cause of death in 90 percent of women who die from breast cancer), this area is being actively investigated.

There is a theory that breast cancer may lie dormant in bone marrow, and the bones which breast cancer most commonly spreads to are those which are rich in bone marrow. If you are interested, you can learn more about the theory of cancer stem cells and dormancy as a possible explanation for why breast cancer can hide for years or decades and then recur.

How Are Bone Metastases From Breast Cancer Diagnosed?

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 due to a metastasis, a pathologic fracture). Other times, bone metastases are diagnosed incidentally when a test such as a PET scan is done for another reason. Tests done specifically to look for bone metastases include bone scans and PET scans, with the combination of PET/CT, SPECT/CT, whole body MRI, and PET/MRI offering further sensitivity. There is some debate over the best test, but your oncologist will take several considerations into account when making a recommendation.

Treatments for Bone Metastases

A number of different treatments are available for bone metastases. The option which 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 treatment options for metastatic breast cancer such as chemotherapy, hormonal therapies, and targeted medications are often used, but other options designed specifically to treat the spread of cancer to bones are often used, and can frequently result in the management of a cancer for quite some time. These may include:

Pain control - Metastases to bones can be very painful, yet there are many different approaches for relieving pain. Finding the right medications and balancing the side effects of these drugs with adequate pain relief can be challenging. If this becomes difficult, some people work with a palliative care physician or a pain specialist to address the best management for their pain.

Radiation therapy - Radiation therapy is often used and can help both to decrease pain and reduce the risk of fractures. Radiation treatments are "local treatments" which means that it works better for isolated areas of metastases than for widespread metastases.

Radiopharmaceuticals - Radiopharmaceuticals are medications which include a particle of radiation attached to another chemical, which can then be injected into the bloodstream. The radiation is thus delivered directly to the bone metastases. Examples include Strontium-89 and Radium-223. Radiopharmaceuticals may be particularly helpful for those who have multiple or extensive bone metastases which would be difficult to treat with local therapies such as radiation therapy. They have relatively few side effects and can be very effective in controlling bone pain.

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

  • Bisphosphonates - Bisphosphonates are medications which were first approved for osteoporosis and then found to be very effective in treating bone metastases. An example is Zometa (zoledronic acid). In addition to reducing complications from bone metastases, these medications appear to have strong anti-tumor effects. For this reason, they are now being considered even for women with early stage breast cancer (who are postmenopausal or premenopausal on ovarian suppression therapy), as they may both help with the bone loss caused by hormonal therapies (such as aromatase inhibitors) and prevent metastases to bone. Bisphosphonates do carry a rare side effect of osteonecrosis of the jaw.
  • Xgeva (denosumab) - Denosumab is an antibody which has been found to be effective in reducing complications (such as fractures) for people with bone metastases from breast cancer. It also appears to have anti-cancer properties. It is given as a subcuticular injection once every four weeks.

Surgery - Surgery is used most often to stabilize fractures or areas of bone at risk for fractures (see below).

Possible Complications From Bone Metastases

Bone metastases can lead to many different symptoms and complications. These include:

Difficult-to-manage pain – The pain which accompanies bone metastases can be severe. Pain is often treated with a combination of pain medications and treatments which are designed to reduce the bone metastases. In addition to pain medications, pain specialists have a number of other therapies, including nerve blocks that are sometimes needed.

Fractures/risk of fractures - It's not uncommon for a person to first learn they have bone metastases after suffering a fracture. (Here is an example of a woman with breast cancer and a pathologic hip fracture due to metastases.) Surgery is often done to repair the fractures. With fractures in the long bones of the arms or legs, a rod is usually placed. Not only does this provide support for a weakened bone, but may allow you to become active more rapidly. Vertebroplasty or "cement" may be used for spinal fractures or impending fractures.

Spinal cord compression - Spinal cord compression is a medical emergency that can be caused by bone metastases. Infiltration of cancer in the lower spine can lead to the collapse of the vertebrae, and in turn, compression of the nerves that leave the spine to travel to the lower half of the body. Symptoms may include worsening lower back pain which may radiate down the legs, weakness or numbness in one or both legs, and loss of bladder and/or bowel control when breast cancer metastasizes to the spine. Surgical procedures are used to stabilize the spine.

Hypercalcemia – As bones are broken down by cancer, calcium is released into the blood. This, in turn, can lead to constipation, fatigue, extreme thirst, and muscle weakness. When severe, untreated hypercalcemia caused by cancer can lead to kidney failure, coma, and death. 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.

Loss of mobility – The impact of decreased activity associated with recovery from a fracture cannot be stressed enough. With studies telling us that exercise can play a role in survival, even with metastatic breast cancer, anything which reduces your ability to be physically active needs to be addressed carefully.

Poor quality of life - Between the pain related to bone metastases, and immobility related to fractures or risk of fractures, bone metastases can significantly reduce your quality of life. Thankfully, as noted above, there are many options for treatment.

Prognosis When Breast Cancer Spreads to Bone

The prognosis of breast cancer which has spread only to bones is somewhat better than for cancers which have spread to other regions of the body. Treatment of bone metastases can sometimes control the disease for a long time. The average overall survival for metastatic breast cancer is 18 to 24 months, with only around 20 percent of people surviving beyond five years. It's important to note again, however, that the prognosis is better for people with only bone metastases and there are some long-term survivors of breast cancer which has spread to bones.

Bottom Line on Bone Metastases Due to Breast Cancer

When breast cancer spreads to bones it can be terrifying, especially when this is the way that you discover that your cancer has recurred and you now have metastatic breast cancer.

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.

Sources:

Coleman, R. Impact of Bone-Targeted Treatments on Skeletal Morbidity and Survival in Breast Cancer. Oncology (Williston Park). 2016. 30(8):pii:218394.

Das, T., and S. Banerjee. Radiopharmaceuticals for Metastatic Bone Pain Palliation: Available Options in the Clinical Domain and Their Comparsions. Clinical and Experimental Metastasis. 2017. 34(1):1-10.

National Cancer Institute. Meta-Analysis Finds Benefits of Adjuvant Bisphosphonates for Postmenopausal Breast Cancer. 09/09/15. https://www.cancer.gov/types/breast/research/adjuvant-bisphosphonates-meta-analysis

O’Sullivan, G., Carty, F., and C. Cronin. Imaging of Bone Metastasis: An Update. World Journal of Radiology. 2015. 7(8):202-211.

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