When cancer spreads to the bone, it can cause very serious complications like broken bones or spinal cord compression. For someone with advanced cancer, bone complications are a serious challenge, yet many people are unaware of this health issue.
If you have cancer, it’s important to be proactive about your bone health. Speak to your doctor if you have persistent, unexplained bone pain, or think you may be at risk of serious bone complications.
When cancer from another part of your body spreads, or metastasizes, to your bones, this is called bone metastases. Bone metastases are also called secondary bone cancer, metastatic cancer in the bone, or secondary cancer in the bone. Patients with bone metastases are at risk for various complications, including pathological fractures (bones breaking spontaneously), hypercalcemia, spinal cord compression. Collectively, complications from bone metastases are called skeletal-related events (SREs). These events are a significant cause of death, loss of mobility and independence, and decrease in quality of life for patients with bone metastases.
Any kind of cancer can spread to a bone. However, it happens more often with certain types of cancer. These are:1
- Breast cancer
- Prostate cancer
- Lung cancer
- Kidney cancer
- Thyroid cancer
As many as 65 to 75 percent of women with advanced breast cancer and up to 90 percent of men with advanced prostate cancer develop bone metastases.2
Myeloma is a blood cancer that develops from bone marrow cells – it often affects the bones too.
Bone metastases are different from primary bone cancer, which originates in the bone. They are also much more common.
Sometimes a secondary bone cancer is found before the primary cancer is known. This may lead to a diagnosis of the primary cancer. Occasionally the primary cancer can’t be found. When this happens, it is called a cancer of unknown primary.3
- Pelvis (hip bone)
- Femur (thigh bone)
- Humerus (upper arm bone)
- Sternum (chest bone)
Signs and complications
This is the most common symptom of bone metastases. The amount varies – different people experience it differently. Many who experience it find it gets worse at night. In some cases it is worse when you are moving. Bone metastases are the most common cause of cancer-related pain.5
Pain is often the first sign of bone metastases. In other cases, however, there are no symptoms at all. About a third of advanced breast cancer patients who develop osteolytic bone metastases feel no pain from them.5
This is when there is too much calcium in the blood. This may show up on a routine blood test. It can also cause a variety of symptoms. Symptoms that occur early on include:4
- Lethargy, sleepiness, sluggishness
- Feeling thirsty all the time
Further symptoms and complications often develop later on, such as:4
- Muscle weakness
- Kidney failure
Bone metastases weakens the bone, increasing the risk of fracture. Sometimes a fracture caused by bone mets may happen spontaneously — this is called a pathological fracture. It often happens to the leg bones near the hip, because these support most of your weight; but can happen in other bones as well. It is often preceded by a lot of pain in the bone. Some preventative treatments include surgery to put a rod through the bone.
Spinal cord compression.
The spine is one the places bone metastases often form. When a metastasis in the spine exerts pressure on the nerves in the spinal cord, that is spinal cord compression.3 It can cause a number of symptoms:
- Back or neck pain. The pain may grow in intensity, and is concentrated in the area where the tumour is. It is often worse at night and when coughing or sneezing. This is the earliest symptom that appears – it may precede other symptoms by weeks or months.3 5
- Weakness in arms or legs, or difficulty moving them. This symptom occurs later on, indicating damage to nerves is beginning to take place.6
- Numbness or strange sensations in the legs, hands, or pelvis. This is also a later symptom. 5
How it happens
There are several reasons that bones are a common site for metastasis – among them: high blood flow within the marrow, certain molecules on tumour cells that bind to certain cells in the marrow, and factors within the bone that provide a good environment for tumour growth.2
Note that when a cancer spreads to a bone – or to anywhere else, for that matter – it is still called by the name of the organ where it originated. It is also treated according to the site where it originated, rather than as bone cancer. (Primary bone cancer, which originates in the bone, is something else, and is much rarer than cancer metastasizing to the bone.)4
Bone is not static: it is continually being broken down and rebuilt. Cells called osteoclasts destroy bone, and cells called osteoblasts build new bone. Normally the actions of these cells are coordinated so that the bone structure is regular, strong, and in good health.1
Bone metastases interfere with this process. They do this by stimulating osteoclasts, so that bone is destroyed without new bone replacing it; or by stimulating osteoblasts, which create bone (sclerotic). Bone metastases exist on a spectrum in which some mostly destroy bone, some mostly build bone, and others do some of both. These are called ‘lytic’, ‘sclerotic’, or ‘mixed’, respectively.2
Both kinds of activity create lesions that are harmful to bone health. Places with extra bone (sclerotic lesions) are just as likely to cause breakage as place where bone has been destroyed (osteolytic lesions, lytic lesions), because the overall structure of the bone has been compromised.4
When a bone has been weakened by lesions from bone metastases can break spontaneously (without an incident like a fall). This is called a pathological fracture. This can be a sign of bone metastases for patients who did not already know they had it.4
Different kinds of cancer tend to produce different kinds of lesions when they spread to the bone. Breast cancer and myeloma mostly create lytic lesions. Prostate cancer mostly creates sclerotic lesions. Both these kinds of cancer usually contain the other kind of lesion too, but not always.5
There is no cure for bone metastases. Treatment can help manage symptoms, reduce pain, and help you live longer.
The main drugs used to treat bone metastases are a class of drugs called biphosphonates, and denosumab. Both biphosphonates and denosumab prevent bone loss by inhibiting the work of osteoclast cells, but they do so by different mechanisms. Both are well-established and have been found to be effective at preventing skeletal-related events (SREs).7
Radiation therapy and surgery are also used. Talk to your doctor about what kind of treatment plan may be best for you.
- Just Breathe: Learning to Live with Bone Mets. An article by Eileen Dahl for the CCSN on living with bone metastases.
- Bone metastases information at the Canadian Cancer Society.
- Secondary bone cancer page at MacMillan Cancer Support (UK).
- Canadian Cancer Society. (2020). “Bone metastases.” https://www.cancer.ca/en/cancer-information/cancer-type/metastatic-cancer/bone-metastases/
- Suva, L., Washam, C., Nicholas, R., & Griffin, R. (2011). “Bone metastasis: mechanisms and therapeutic opportunities.” Nature Reviews Endocrinology 7: 208-211. https://doi.org /10.1038/nrendo.2010.227
- MacMillan Cancer Support. (2019). Understanding Secondary Cancer in the Bone. Retrieved August 2020 from https://www.macmillan.org.uk/cancer-information-and-support/stories-and-media/booklets/understanding-secondary-cancer-in-the-bone
- American Cancer Society. (2016). “Understanding Advanced Cancer, Metastatic Cancer, and Bone Metastasis.” Retrieved August 2020 from https://www.cancer.org/treatment/understanding-your-diagnosis/advanced-cancer/what-is.html
- Coleman, R. E. (2006). “Clinical Features of Metastatic Bone Disease and Risk of Skeletal Morbidity.” Clinical Cancer Research 12(20): 6243s-6249s. https://doi.org/10.1158/1078-0432.CCR-06-0931
- American Cancer Society. (2016). “Managing Symptoms of Bone Metastases.” Retrieved August 2020 from https://www.cancer.org/treatment/understanding-your-diagnosis/advanced-cancer/managing-symptoms-of-bone-metastases.html
- Burgess, Leslie. (2013). “Preventing Skeletal-Related Events in Patients With Solid Tumors.” Cancer Therapy Advisor. Retrieved August 2020 from https://www.cancertherapyadvisor.com/home/cancer-topics/bone-cancer/preventing-skeletal-related-events-in-patients-with-solid-tumors/