When Cancer Spreads to Bone

By: Gabriel N. Hortobagyi, MD
By: Paul Mathew, MD
By: Nora Janjan, MD
Though there are many different types of cancer cells, which can originate in any area of the body, they all have one very important characteristic in common. Unlike normal cells, cancer cells do not know when to die. And as they grow in numbers, they spread to other tissues and organs. One area of the body that is particularly receptive to spreading cancer cells is the bone.
Bone is a rich repository of substances that enhance the growth of tumor cells. When cancer reaches the bone, a vicious cycle begins. The tumor cell produces substances that enhance the destruction of normal bone. In turn, the destruction of normal bone ends up in the release of substances that encourage the growth of cancer cells.

Below, three experts in the area of skeletal complications of cancer offer an introduction to this insidious and deadly cycle.

Dr. Hortobagyi, what exactly are skeletal complications in cancer?
GABRIEL N. HORTOBAGYI, MD: Skeletal complications are complications that develop when cancers of different origin spread to bone. The weakening bone can produce a number of symptoms and problems related to the condition of the patient.


Can you explain the difference between primary bone cancer and metastatic bone cancer? Which is more common?
PAUL MATTHEW, MD: Primary bone cancer refers to a tumor that originated in the bone whereas the metastatic bone cancer refers to cancer that originated in another organ, and spread or metastasized to bone. Metastatic cancer, or "secondary bone cancer", is much more common, originating from common cancers such as lung cancer, breast and prostate cancer.

What are your first considerations when someone has cancer that has spread to the bone?
NORA JANJAN, MD: Well they cause significant problems. Patients can have a lot of pain due to complications from bony metastases. In those cases, we have three very important things to consider. First of all, we need to relieve the patient's suffering and we do that with pain medication. It's very important that the patient doesn't waste energy on pain when they could use that energy to fight the cancer.

The second thing we do is address the problem itself. We determine whether or not surgery is needed to stabilize the bone, or radiation therapy, a localized treatment to make that bone stronger in that location. And third, we have to realize that when cancer moves to the bone, it means we're seeing a spread of the cancer. So systemic therapies have to be used to treat the cancer as it goes throughout the whole system.

How are metastatic bone cancers classified?
NORA JANJAN, MD: They can be what we call "lytic", which means that they eat away at the bone. They cause a hole in the bone and weaken it. Or they can be "blastic", and that means that they make the bone very dense. When you look on an X-ray they look very thick. In either case, the bone metastases can cause similar symptoms. And oftentimes we see a mixed reaction, where you have a little bit of both of the types of cancer involving the bone that we've talked about -- the lytic and the blastic together.
Dr. Hortobagyi, what symptoms and signs do your patients experience when they have the skeletal complications of cancer?
GABRIEL N. HORTOBAGYI, MD: When cancer cells develop in bone or spread to bone, they weaken its normal structure and can produce a variety of symptoms. Number one is pain. They can produce fractures. They can produce symptoms related to abnormalities in calcium concentration in the blood stream. They can produce compression of nerves in the spinal cord. All of these are referred to as skeletal complications. Some are more serious than others, but all contribute to disability and compromised well-being for these patients.

Can you expand on the impaired mobility?
GABRIEL N. HORTOBAGYI, MD: Impaired mobility occurs for a variety of reasons. Pain itself can cause impaired mobility. If you know that every time you make a certain movement, it causes pain, you will stop making that movement. If you develop a fracture -- and common fractures occur in hips, spine, vertebrae and ribs -- all these areas can cause impaired mobility. These are very important complications that reduce the quality of life of patients.

PAUL MATTHEW, MD: Another important complication is the strategic advantage that some cancers enjoy as a result of spread to bone. Clearly there must be a unique relationship that these cancers, such as prostate cancer, have with what we refer to as the "microenvironment", the bone. So there is something about the bone microenvironment that allows the cancer cells to flourish and proliferate. Research has shown that targeting the bone specifically might alter the natural history of the disease. Not just improve quality of life, but perhaps quantity.

Dr. Janjan, how are primary and metastatic bone cancers diagnosed?
NORA JANJAN, MD: Patients with primary bone cancer come in with symptoms of pain and a biopsy will be performed to determine a diagnosis. Oftentimes we can diagnose spread of prostate or breast cancer to the bones through X-rays, and in that case we don't necessarily have to biopsy that again. It's very important for patients to understand the potential areas of spread for the cancer and to alert their physicians when they know there is something new because early diagnosis is always our best way of handling things.
What about bone scans, MRIs or simple blood tests?
NORA JANJAN, MD: Simple blood tests sometimes will alert us that the cancer has either recurred or has spread because there are blood tests that will become elevated if the cancer continues to grow. But that doesn't alert us to bone specifically.

So if a patient has a symptom in a specific site, we might do an X-ray of that site to evaluate it. Bone scans, or MRIs, are very sensitive. The diagnostic tool depends on the site that's involved.

Dr. Matthew, what are the goals when treating patients with skeletal complications of cancer?
PAUL MATTHEW, MD: Relief of symptoms and preserving function are two of the most obvious, immediate needs. Cancer is, by virtue of its behavior, uniquely dependent on the bone microenvironment for its growth and proliferation. But I think that there are opportunities for altering the natural history of the cancer as well, for example with bisphosphonates and other drugs in development.


Dr. Hortobagyi, can you explain why bisphosphonates are helpful in the treatment of skeletal complications of cancer?
GABRIEL N. HORTOBAGYI, MD: What bisphosphonates do very effectively is to interfere with the excessive activity of the type of bone cells that destroy normal bone. And by doing that, they restore, to some extent, the balance or the equilibrium between the two types of bone cells. There are some types of bisphosphonates that may have some direct effect over cancer cells themselves, although that is still under investigation.

Any final thoughts?
NORA JANJAN, MD: I think patients should realize that cancer is now often being considered a chronic disease. There are many patients who have cancer for a long time and they're able to function and continue their life. It's our hope with these new treatments for metastatic disease involving bone that we can relieve symptoms like pain, prevent them from having other symptoms caused by the cancer, and help them maintain and continue their life as well as possible.

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