Treating Weak Bones in Cancer Patients

By Erica Heilman
Bone is one of the most popular destination sites for cancer cells that are migrating from one area in the body to another. On arrival, these cancer cells begin a systematic process of weakening and damaging the skeletal system. But bone has another, more unlikely enemy: cancer treatment. Many treatments for cancer actually contribute to bone loss and the development of osteoporosis. But people are living longer with cancer, and bone complications can persist long after treatment has successfully managed the malignancy, causing pain and risk of debilitation. Below, Dr. Bob Smith from South Carolina Oncology talks about why certain cancer patients are at particular risk for bone complications, and ways to avert some potential consequences.

How prevalent are bone complications in cancer?
They are particularly problematic for people with prostate cancer, metastatic breast cancer, multiple myeloma or diseases where, due to fairly long expected survivals, the bone complications become a crucial element impacting the quality of life. Lung cancer, for instance, frequently will involve bones, but the patient has a shorter expected survival, and other problems become more important to a patient with lung cancer.

But myeloma, prostate cancer and breast cancer are all diseases that almost universally will affect the bone in advanced disease, and at the same time, the people that have those illnesses can now live for a long time with treatments. We frequently have people whose malignancy is under excellent control, and yet they have ongoing bone pain and bone complications because of osteoporosis and damage to the bone structure by the cancer. So it's very important for us to use treatments to prevent bone problems and reduce this damage as much as possible.

Why does cancer spread to bone?
Bone is 'fertile soil' for certain cancer cells to settle in, then grow and cause problems. Of course multiple myeloma, which is primarily a disease of the bone marrow, so naturally that affects bone.

What additional risks do these complications cause in people with cancer?
There are a few problems. First is pain. Second, these bone complications can lead to osteoporosis, which makes patients more susceptible to fracture. They are also at greater risk of compression fractures of their spine, and dangerously high calcium levels.

Can the treatments for cancer also put patients at risk for bone problems?
We're finding that more and more treatments cause osteoporosis. Chemotherapy causes osteoporosis. Hormonal treatments cause osteoporosis. Aromatase inhibitors, which are treatments for breast cancer that affect hormonal levels, are very effective drugs with few side effects or complications, but they do increase the amount of osteoporosis that occurs.
What is the treatment for bone complications?
There are a number of treatments. Radiation therapy is effective in treating bone pain in particular areas, and surgery is used to address bone fractures. To strengthen bone and prevent a lot of complications from happening in the first place, we use bisphosphonates, which are a class of drugs that have been around for a while to treat osteoporosis. Newer more potent formulations have become very easy to use.

Why are breast cancer patients more susceptible to bone complications?
Currently, the gold standard treatment for hormone-dependent breast cancer is tamoxifen. And I anticipate in the next few years that most women will begin being treated with another type of hormone therapy called aromatase inhibitors, rather than tamoxifen. The side effects of the new aromatase inhibitors are minimal. But in fighting the cancer, these drugs deprive the bone of estrogen, and estrogen is very important in the prevention of osteoporosis. So we are going to have to develop effective treatment schedules that address both the cancer and the pending bone complications at once.

Why are men with prostate cancer at greater risk of bone complications?
Men with prostate cancer are also at high risk of osteoporosis. We now use hormonal therapies that prevent testosterone production. In the male, estrogen, which is necessary to prevent osteoporosis, is produced from testosterone. As a result, the same drugs that are very effective at treating prostate cancer, also cause osteoporosis. It's becoming a major problem in men with prostate cancer because we're treating it earlier with hormonal therapy, and they have very long survivals.

How does multiple myeloma affect bone?
Multiple myeloma, just by the nature of its malignant cells, causes osteoporosis to develop diffusely. You also have lesions in the bone that cause destruction of localized area of bone and make it especially prone to fracture. So you've got the generalized osteoporosis and multiple sites of damage to the bone structure. This is a disease where bisphosphonates are especially important, and we start patients on them as soon as multiple myeloma is diagnosed.

Are there side effects with bisphosphonates?
Their side effects are minimal. With intravenous bisphosphonates, there is some bone pain on the day of injection. Sometimes there's a low-grade fever for a short period of time. Also, these drugs can affect a person's kidney function, and there is the potential of kidney damage. It's important to monitor function regularly, and if there is a problem, we increase the amount of time of administration of the drug.

How are bisphosphonates being used now to treat cancer-related bone complications?
At this point, bisphosphonates are used routinely only in patients with documented bone metastases. Clinical trials are underway that will determine the benefit of using bisphosphonates in adjuvant settings-in other words, in conjunction with cancer treatments to prevent bone deterioration caused by those treatments. What we will see in the near future is those trials coming out.