Bone Metastases - Overview

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The spread of cancer from its site of origin to another location in the
body is called metastasis. Cancer cells can spread, or metastasize,
through the blood and lymph systems. Bone metastases usually occur by way
of the bloodstream. A cancer cell may break away from the original
location in the body and travel in the circulatory system until it gets
lodged in a small capillary network in bone tissue. Cancer may also spread
to bone by erosion from the adjacent cancer, though this occurs less
frequently than spread by the bloodstream.

Bone is one of the most common locations in the body to which cancer
metastasizes. The major cancer types that tend to metastasize to bone
include multiple myeloma, breast, prostate, lung, kidney, and thyroid
cancers. Bone metastases may cause pain, may make the bones more
susceptible to fractures, and may cause increased levels of calcium in the
blood.

Bone metastases result in lesions or injury to the bone tissue. There are
two types of lesions: lytic lesions, which destroy bone material; and
blastic lesions, which fill the bone with extra cells. Normal bone is
constantly being remodeled, or broken down and rebuilt. Cancer cells that
have spread to the bone disrupt the balance between the activity of
osteoclasts (cells that break down bone) and osteoblasts (cells that build
bone).

Bone metastases generally occur in the central parts of the skeleton,
although they may be found anywhere in the skeletal system. Common sites
for bone metastases include the back, pelvis, upper leg, ribs, upper arm,
and skull. More than 90% of all metastases are found in these locations.
Complications Associated with Bone Metastases

Complications that are associated with bone metastases include pain, bone
loss, hypercalcemia, and decreased blood cell production.

Pain: A common complication, and often the initial symptom of bone
metastases, is bone pain. The thick membrane that covers each bone, called
the periosteum, has many nerves, making it a highly sensitive tissue.
Damage or pressure to this tissue caused by bone metastases may result in
a great deal of pain. Bone pain can be debilitating to the point that it
compromises a patient's ability to manage normal day-to-day activities.
Bone pain due to metastases may be hard to differentiate from ordinary low
back pain or arthritis. The most notable difference is that pain due to
bone metastasis is typically more constant, even at night.


Bone loss: Bone loss occurs when there is decreased calcification or
reduced density of the bones. The result is weak bones that are at
increased risk of fracture. Bone loss in the leg or hip bones can be a
serious condition because these are major weight-bearing bones and
fractures in these areas are often debilitating.


Hypercalcemia:An increased level of calcium in the bloodstream is called
hypercalcemia. This disorder results from the destruction of bone
associated with metastases. Hypercalcemia can be a life-threatening
condition.

Symptoms of hypercalcemia may include:
Nausea
Fatigue
Vomiting
Lethargy
Stomach Pain
Moodiness
Constipation
Irritability
Anorexia
Confusion
Excessive thirst
Extreme muscle weakness
Dry mouth or throat
Irregular heart beat
Frequent urination


Coma

These many signs and symptoms make it difficult for doctors to correctly
diagnose hypercalcemia. Consequently, they are commonly attributed to
either the cancer treatment or the malignancy itself. This disorder can be
severe and difficult to manage. Severe hypercalcemia is a medical
emergency requiring immediate treatment.

Learn more about the management of Hypercalcemia

Decreased blood cell production: Bone metastases can also cause a decrease
in blood cell production. The multiplication of cancer cells in the bone
marrow eventually crowds out and suppresses the normal production of blood
cells. This may cause a significant decrease in red blood cells,
platelets, and white blood cells, which can cause anemia, abnormal
bleeding, and neutropenia, respectively. Anemia decreases the body's
ability to transport oxygen to the body's organs. Anemia may cause
patients to experience tiredness, fatigue, shortness of breath, and/or a
reduced tolerance to activity. Neutropenia, or the depletion of white
blood cells, compromises the immune system and makes patients more
susceptible to infection.

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Surgery

Although surgery to remove a primary bone tumor (one that started in the
bone) is often done with the intent to cure, the purpose of treating a
bone metastasis surgically is to relieve symptoms. Bone metastases can
weaken bones, leading to breaks that tend to heal very poorly. An
operation to stabilize the bone with a metal rod or external device can
prevent some fractures and, if the bone is already broken, can rapidly
relieve pain and help the patient return to usual activities.

If you can?t have surgery to reinforce a bone affected by metastasis
(because of poor general state of health, other complications of the
cancers, or side effects of other treatments) a cast may help stabilize
leg bones to reduce pain and avoid the need to stay in bed.

Sometimes the cancer will spread to a bone in the spine. The cancer can
grow enough to press against the spinal cord (spinal cord compression). If
not treated immediately, this can lead to paralysis. Surgery can relieve
the pressure on the spinal cord and prevent paralysis as well as help
relieve the pain. Radiation therapy is another option. A recent study has
found that surgery followed by radiation may be the best treatment.

Radiation therapy uses high-energy rays or particles to destroy cancer
cells or slow their rate of growth. Radiation therapy can be used to cure
primary cancers that have not spread too far from their original site.
When a cancer has metastasized to bones, radiation is used to relieve
(palliate) symptoms. Radiation may prevent fractures once the bone has
healed. But this takes time and if there is a impending risk of a bone
fracture, radiation will not prevent this. Instead the bone must be
stabilized with surgery (see below).

External beam radiation: The most common way to deliver radiation to a
bone metastasis is to carefully focus a beam of radiation from a machine
outside the body. This is known as external beam radiation. To reduce the
risk of side effects, doctors carefully figure out the exact dose and aim
the beam as accurately as they can to hit the target.

External beam radiation therapy for bone metastasis can be given as a
large dose at one time, or in smaller amounts over 5 - 10 treatments. Most
radiation oncologists (doctors who specialize in radiation therapy) prefer
to give the radiation over several treatments. Both provide the same
benefit in pain reduction and when asked, most patients prefer the single
does treatment. The advantage of the 1-dose treatment is fewer trips for
therapy and it costs less. The advantage of more treatments is that it
reduces the number of patients who need re-treatment (because the pain has
come back) from about 18% to around 9%.

Each treatment lasts only a few minutes. External beam radiation is an
excellent option if you have 1 or 2 metastases that are causing symptoms.
But if there are many metastases scattered throughout the body, treatment
is more difficult. In rare cases, some patients can benefit from radiation
therapy to the entire upper or lower half of their bodies. A few weeks
later, the other half of the body can be treated.

Radiopharmaceuticals (Strontium-89 and Samarium-153)

Strontium-89 (Metastron) and samarium-153 (Quadramet) are drugs called
radiopharmaceuticals. They are not used to treat early stage, localized
cancer but are used to treat bone pain caused by some types of metastatic
cancer.

Radiopharmaceuticals are a group of drugs that have radioactive elements.
They are injected into a vein and settle in areas of bone that contain
cancer. The radiation they give off kills the cancer cells and relieves
some of the pain caused by bone metastases. Other radiopharmaceuticals,
such as rhenium-186 and rhenium-188, are also being studied.

If cancer has spread to many bones, this approach is much better than
trying to aim external beam radiation at each affected bone. In some
cases, they may be used together with external beam radiation aimed at the
most painful bone metastases.

These drugs work best when the metastases are osteoblastic. Osteoblastic
means the cancer has stimulated the bone cells (osteoblasts) to form new
areas of bone. These areas appear dense (white) on x-rays (as opposed to
osteoclastic lesions, which appear as dark areas or holes in the bones).
Osteoblastic metastases occur most frequently in prostate cancer that has
spread to bone. They are found less often in breast cancer that has spread
to bone and even less often in most other cancers.

The major side effect of this treatment is a lowering of blood cell counts
(white cells and platelets), which could place you at increased risk for
infections or bleeding, especially if your counts are already low.

Surgery

Although surgery to remove a primary bone tumor (one that started in the
bone) is often done with the intent to cure, the purpose of treating a
bone metastasis surgically is to relieve symptoms. Bone metastases can
weaken bones, leading to breaks that tend to heal very poorly. An
operation to stabilize the bone with a metal rod or external device can
prevent some fractures and, if the bone is already broken, can rapidly
relieve pain and help the patient return to usual activities.

If you can?t have surgery to reinforce a bone affected by metastasis
(because of poor general state of health, other complications of the
cancers, or side effects of other treatments) a cast may help stabilize
leg bones to reduce pain and avoid the need to stay in bed.

Sometimes the cancer will spread to a bone in the spine. The cancer can
grow enough to press against the spinal cord (spinal cord compression). If
not treated immediately, this can lead to paralysis. Surgery can relieve
the pressure on the spinal cord and prevent paralysis as well as help
relieve the pain. Radiation therapy is another option. A recent study has
found that surgery followed by radiation may be the best treatment.

Pain Medications for Bone Metastasis

There are effective and safe ways to treat pain caused by bone metastasis.
In some cases, this may include treatments that kill the cancer cells
(chemotherapy or radiation therapy), slow their growth (hormonal therapy),
or reduce bone damage (bisphosphonates). If the treatment does not relieve
your pain, you should not hesitate to ask for pain medicines.

You may not want to ask for or accept pain medicines such as opioids
because you think you will become addicted or that the medicines will make
you too sleepy to continue your usual activities. In reality, addiction
rarely occurs, drowsiness can be controlled, and being free of pain can
help you concentrate on the activities that are important to you.

If you are in pain and have been given prescription pain medicines, you
should take them on a regular schedule. It is better to prevent the pain
than to treat it once it starts. For more information on management of
pain, please see "Pain Control: A Guide for People with Cancer and their
Families."