Bone Metastases: When Cancer Spreads to the Bones
Cancer that has started in one place can spread and invade other parts of the body.
This spreading is called metastasizing. If a tumor spreads to the bone, it is called
Cancer cells that have spread to the bone can damage the bone and cause symptoms.
Different treatments are available to control the symptoms and the spread of bone
metastases. To better understand what happens in metastasis, it helps to understand
the anatomy of the bones.
Bone is a type of connective tissue made up mostly of minerals, such as calcium and
phosphate, and a type of protein called collagen. The outer layer of bone is called
the cortex. The spongy center of bone is called bone marrow.
Bone is alive and always repairing and renewing itself through a process called remodeling.
Two kinds of cells help with this process:
Osteoblasts are bone-forming cells.
Osteoclasts are cells that break down, or reabsorb, bone.
Below are some of the functions bones perform:
The skeleton gives structural support.
Bones store and release, as needed, minerals that the body needs to work properly,
such as calcium.
Bone marrow makes and stores blood cells. These include red blood cells, white
blood cells, and platelets. Red blood cells bring oxygen from the lungs to the
rest of the body. White blood cells fight infections. Platelets help the blood
When cancer cells invade the bone, any or all of these bone functions may be affected.
How cancer spreads to the bone
When cells break away from a cancerous tumor, they can travel through the bloodstream
or lymph vessels to other parts of the body. Cancer cells can lodge in an organ at
a distant location and start a new tumor. The original tumor that cells break away
from is called the primary tumor. The new tumor that the traveling cells create is
called the secondary tumor. Secondary tumors in the bone are called bone metastases.
Different types of cancer seem to spread to certain sites in the body. For example,
many types of cancer commonly spread to the bone. The bone is a common site of metastasis
for these cancers:
Bone metastases are not the same as cancer that starts in the bone. Cancer that starts
in the bone is called primary bone cancer. There are different types of primary bone
cancers, such as osteosarcoma. A tumor that has metastasized to bone is not made of
bone cells. Bone metastases are made up of abnormal cancer cells that start from the
original tumor site. For example, lung cancer that spreads to the bone is made of
lung cancer cells. In this case, bone metastasis would be called metastatic lung cancer.
Cancer cells that spread to the bone often stay in these places:
Cancer cells that spread from other parts of the body can form 2 main types of bone
The tumor may eat away areas of bone, creating holes called osteolytic lesions.
This can make bones fragile and weak, so that they break or fracture easily.
These areas may be painful.
The tumor may stimulate bone to form and build up abnormally. These areas of
new bone (osteosclerotic or osteoblastic lesions) are weak and unstable, and
may break or collapse. They can also be painful.
Symptoms of bone metastases
Bone metastases can cause the following symptoms:
Bone pain. Pain is the most common symptom of bone metastasis. It's often the
first symptom you notice. At first, the pain may come and go. It tends to be
worse at night or with bed rest. Over time, the pain may grow and become severe.
Not all pain means metastasis. Your doctor can help tell the difference between
pain from metastasis and aches and pains from other sources.
Broken bones. Bone metastasis can weaken bones, putting them at risk for breaking.
In some cases, a break (fracture) is the first sign of bone metastasis. The most
common sites of fracture are the long bones of the arms and legs, and the bones
of the spine. A sudden pain in the middle of your back may mean that a cancerous
bone is breaking and collapsing.
Numbness or weakness in the legs, trouble urinating or having a bowel movement,
or numbness in the belly. These are all signs that the spinal cord may be compressed.
When cancer metastasizes to the spine, it can squeeze the spinal cord. The pressure
on the spinal cord may cause these symptoms, as well as back pain. If you have
these symptoms, you should tell a doctor or nurse right away. If untreated, it can
Loss of appetite, nausea, thirst, constipation, tiredness, or confusion. These
are all signs that you may have high levels of calcium in your blood. Bone metastases
can cause a release of calcium into the bloodstream. This condition is called
hypercalcemia. If you have these symptoms, you should tell a doctor or nurse
right away. If untreated, it may cause a coma.
Other symptoms. If bone metastasis affects your bone marrow, you may have other
symptoms related to lower blood cell counts. Your red blood cell levels may drop,
causing anemia. Signs of anemia are tiredness, weakness, and shortness of breath.
If white blood cells are affected, you may get infections. Signs of infection
include fevers, chills, fatigue, or pain. If the number of platelets drops, bruising
or abnormal bleeding may occur.
It is important for you to discuss any of these symptoms with your doctor. Finding
and treating bone metastasis early can help reduce complications.
How doctors find and diagnose bone metastasis
In some cases, your doctor may find bone metastasis before you have symptoms. In some
cancers, where bone metastasis is common, your doctor may order tests to make sure
the cancer has not spread to your bones, before recommending treatment. When you have
symptoms of bone metastasis, doctors can do the following tests to find the cause:
Bone scan. A bone scan can often find bone metastasis earlier than an X-ray can. The scan looks
at your whole skeleton. It allows the doctor to check the health of all the bones
in your body, including how they respond to treatment. In a bone scan, the doctor
injects you with a low level of radioactive material. The amount is much lower than
that used in radiation therapy. The radioactive substance is attracted to diseased
bone cells all over the body. This helps diseased bone show up more clearly on the
bone scan image.
CT scan. This imaging test shows detailed images of any part of the body, including the bones.
It is more detailed than a regular X-ray. It uses a combination of X-rays and computer
technology to make cross-sectional images of the body. These images are combined into
1 detailed picture to show if cancer has spread to the bones.
MRI. An MRI scan uses radio waves and strong magnets, instead of X-rays, to make pictures
of bones and tissues. MRI provides cross-sectional images of the body, as a CT scan
does. It is very useful in looking at the spine and spinal cord, as well as joints.
Often, an MRI helps to further check a bone mass seen on an X-ray.
X-rays. An X-ray image can show where in the skeleton the cancer has spread. X-rays also show
the general size and shape of the tumor or tumors. It's common for more than 1 metastasis
to be found.
PET scan. This imaging test uses a type of sugar that is radioactive. This sugar is injected
into your blood. Cancer cells absorb large amounts of the sugar, compared to normal
cells. After the injection, you lie on a table in a PET scanner, while your whole
body is imaged. A special camera takes pictures of the radioactive areas found in
your body. A PET scan is not very detailed, but can sometimes find tumors too small
to be seen on other tests. If an abnormal area is seen, your doctor will likely order
another test for more information. This may be a CT scan or MRI. New technology combines
PET and CT scans for more detailed images all at once.
Lab tests. Bone metastasis can cause many substances to be released into the blood in amounts
that are higher than normal. Two such substances are calcium and an enzyme called
alkaline phosphatase. Blood tests for these substances can help diagnose bone metastasis.
Doctors can also measure the levels of these chemicals over time to check your response
to treatment. Higher levels of these substances can be a sign of other health problems
Biopsy. Your doctor may recommend a bone biopsy to be sure there is bone metastasis. A sample
of bone is removed and checked under a microscope. This is often done when imaging
tests and blood tests suggest, but don't confirm, you have metastasis.
How bone metastasis is treated
In addition to treating the cancer, these treatment options are available for bone
Bisphosphonates (medicines that slow down bone cells called osteoclasts)
Denosumab (another medicine that slows down osteoclasts)
Radiation therapy and radiopharmaceuticals (radioactive medicines)
Chemotherapy, hormone therapy, targeted therapy, or immunotherapy to treat the cancer
Other treatments, including physical therapy and pain medicines
These medicines slow the progression of abnormal bone destruction and formation that
bone metastases cause. The medicines do the following:
Decrease your risk for fractures
Reduce bone pain
Lower high blood calcium levels
Slow bone damage that metastases cause
Different types of bisphosphonates are available, such as:
Each has somewhat different effects. Bisphosphonates in cancer treatment are often
given through an IV (intravenous) line every 3 to 4 weeks. They are also available
as pills that you swallow. But the pills are not well absorbed and can irritate the
GI (gastrointestinal) tract. The side effects of bisphosphonates are usually mild
and don’t last long. Some of the most common side effects are:
Lack of appetite
Researchers are also trying to see if bisphosphonates can prevent bone metastases
from starting, or from coming back.
Doctors sometimes give this medicine in place of a bisphosphonate. It is given either
by IV or injected under the skin every 4 weeks.
Doctors may also prescribe denosumab if bisphosphonates stop working. Denosumab can
help prevent or delay problems like fractures in people with bone metastases.
Radiation therapy and radiopharmaceuticals
Radiation therapy uses high-energy ionizing radiation to hurt or destroy cancer cells. Radiation
is often helpful in easing pain and killing tumor cells in bone metastases. It may
also be used to help prevent fractures and to treat spinal cord compression. It may
take 2 to 3 weeks for the full effects of this treatment to occur. Side effects of
radiation may include skin changes in the area being treated. In rare cases, it may
cause a short-term increase in symptoms of bone metastasis.
Radiopharmaceutical therapy is another type of radiation. This approach involves injecting
a radioactive substance into a vein. The substance is attracted to areas of bone that
have cancer. Giving radiation directly to the bone in this way destroys active cancer
cells in the bone and can ease symptoms. It is often very useful if many bones are
affected. Two important side effects are lower blood counts and greater risk for bleeding.
In rare cases, there is a greater risk of leukemia.
Chemotherapy, hormone therapy, targeted therapy, and immunotherapy
These different types of medicine treatments are often used for advanced cancers.
Depending on the type of cancer you have, these treatments might be used to help treat
cancer that has spread anywhere in the body. They can sometimes help treat bone metastases
by helping to control tumor growth, reduce pain, and lower the risk for bone fractures.
Surgeons sometimes perform surgery for bone metastases to prevent or treat a bone
fracture. The surgery can involve removing most of the tumor or stabilizing the bone
to prevent or manage a fracture, or both. Metal rods, plates, screws, wires, or pins
may be surgically inserted to strengthen or provide structure to the bone damaged
by metastasis. Another example is kyphoplasty. The surgeon injects bone cement into
1 of the bones in the spine to help keep it from collapsing.
Other treatments for bone metastases and their symptoms include physical therapy,
and controlling pain with or without medicine. Doctors use many different medicines
or combinations of medicines to treat pain from bone metastases. The main types of
medicines used to treat this pain are NSAIDs (nonsteroidal anti-inflammatory drugs).
These include aspirin and ibuprofen. They stop the substances (prostaglandins) that
seem responsible for much bone pain. Other ways to manage pain without medicine include
using heat and cold, relaxation methods, and therapeutic beds or mattresses.
Researchers are studying new ways to better manage bone metastases. These new methods
are tested in clinical trials.