How Are Bone Metastases Diagnosed?
Bone metastases are sometimes found because they cause problems, but in some cases, they’re found before you have any symptoms. Your doctor may do lab tests and imaging tests (like x-rays or bone scans) to see if and/or how far the cancer has spread. These tests may show bone metastases.
Imaging tests to find bone metastases
Imaging tests use x-rays, magnetic fields, or radioactive substances to create pictures of the inside of the body. Imaging tests may be done before, during, and after cancer treatment for a number of reasons, including to help find out if cancer has spread to the bones (or any other part of the body). People who are suspected of having bone metastases often have one or more of these tests.
Regular x-rays may show signs of the cancer’s spread to the bones. X-rays are often among the first tests done if a person with cancer is having bone pain or other symptoms.
In osteolytic (OS-tee-oh-lit-ik) or lytic (LIT-ik) metastases, the cancer cells dissolve the bone, making part of it less dense. If the cancer has destroyed enough of the bone, these changes look like a darker hole in the gray-white bone seen on the x-ray.
Osteoblastic or blastic metastases cause an area of the bone to look denser or sclerotic. On x-rays, these metastases show up as spots that are whiter than the bone around them.
Often, bone metastases have both lytic and blastic features.
X-rays can also show fractures (breaks) in bones that have been weakened by metastases.
This test shows the entire skeleton, and can sometimes show a bone metastasis that’s not yet causing symptoms. It’s best at showing metastases that are blastic (where bone is denser).
Bone scans can usually find metastases much earlier than regular x-rays. Bone scans can also be repeated over time to track how the metastases respond to treatments.
Sometimes bone scans fail to find cancer that has spread to the bones. Bone scans have a harder time detecting metastases that are purely osteolytic (where bone is less dense).
Computed tomography (CT)
The CT scan makes detailed cross-sectional images of your body. Sometimes, a CT scan can help tell if the cancer has spread into your bones. It may be used when bone metastases are likely to be osteolytic, since these metastases sometimes don’t show up well on bone scans. CT scans are also good for judging the size and shape of a tumor in the bone and for assessing how stable a bone containing a tumor is (how likely it is to break).
CT-guided needle biopsy: CT scans can also be used to guide a biopsy needle into a suspected area of bone metastasis deep in the body. You stay on the CT scanning table while a doctor guides the needle through your skin and toward the suspicious area. CT scans are repeated until the needle has reached the right place. A fine needle biopsy sample (tiny piece of tissue) or a core needle biopsy sample (a thin cylinder of tissue) is then taken out and checked in the lab to see if there are cancer cells in it.
Magnetic resonance imaging (MRI)
MRI scans use radio waves and strong magnets instead of x-rays to make very detailed pictures of parts of the body. Like a CT scan, MRI produces detailed cross-sectional slices of the body.
Because an MRI scan is very useful for looking at the spine and spinal cord, it’s the standard test used if spinal cord compression is suspected. MRIs are also good at finding problems in bones and joints. Often an MRI scan is done to better define a bone mass seen on an x-ray. MRI scans can usually tell if the mass is likely to be a tumor, an infection, or some type of bone damage from other causes.
Positron emission tomography (PET)
For a PET scan, you are injected with a slightly radioactive form of sugar, which collects mainly in cancer cells. A special camera is then used to create a picture of areas of radioactivity in the body.
This test can sometimes find tumors that are too small to see on other imaging tests. PET scans look at the whole body at once, so they are sometimes used when your doctor thinks the cancer has spread but doesn’t know where.
PET scans can give useful information, but they aren’t very detailed. If an area on the scan looks like it could be cancer, other tests such as MRI or CT scans can be used to check it out further. Special machines can combine PET and CT scans (PET/CT scanners) to give more details on areas of cancer spread.
When cancer spreads to the bones, certain substances that can be found by routine lab tests might be released into the blood. For example:
- Calcium: Bone metastases can dissolve the bones, leading to a high blood calcium level (called hypercalcemia [HI-per-kal-SEE-me-uh]). Problems other than bone metastases can cause high calcium levels, but if a person with cancer has a high blood calcium level, tests are often done to look for bone metastases.
- Alkaline phosphatase: When the bones dissolve, the levels of alkaline phosphatase or ALP may increase. Alkaline phosphatase is also made by the liver, so high ALP levels can mean liver problems. (They don’t always mean bone metastases.)
Several substances can be released into urine when bone is damaged. One substance that can be measured is called N-telopeptide.
Biopsies used to find bone metastases
In most cases, cancer is diagnosed by removing a piece of body tissue and looking at it under a microscope. This procedure is called a biopsy.
If you’ve been diagnosed with cancer or have had cancer in the past, your doctor may be able to tell if you have bone metastasis based on the results of imaging tests such as a bone scan. If any of your blood test results also suggest bone metastasis, this makes the diagnosis even more certain. When this is the case, your doctor might not need to get a tissue sample. But if it’s not clear from tests if the cancer has spread to the bones, your doctor might take a sample from the changed bone to find out if it’s cancer.
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Last Medical Review: May 2, 2016 Last Revised: May 2, 2016