Protecting Bone From Breast Cancer
Erica Heilman
Many people who have experienced cancer live with the fear that the cancer will spread to other areas of the body. Although the patterns of migration vary, bone is often fertile ground for the growth of tumor cells, and is a popular destination for many cancers?including breast cancer. Once there, cancer of the bone can cause severe pain, weakness or fracture, but these symptoms often do not occur until the malignancy is fairly advanced.

But for many women with breast cancer, there is one less intuitive reason why bone complications pose a serious risk?medication. Approximately two-thirds of women with breast cancer are "hormone-receptor positive." meaning their cancer relies on estrogen to fuel its growth. Newer hormonal therapies for breast cancer?such as aromatase inhibitors?are very effective in depriving the body of estrogen, thus slowing the growth of cancer. But reducing estrogen can also rob a woman?s body of its natural protector of bone.

Women ordinarily experience slow, progressive bone loss starting at around age 35 when estrogen levels begin to decrease. When these levels fall off dramatically during menopause, the process of bone loss gains speed. Women taking hormonal therapies that block estrogen experience a kind of ?super-menopause.? For them, bone loss, if left unchecked, is nearly inevitable.


Dr. Ernest Greenberg is a clinical associate professor of medicine at Cornell University Medical College. In the following conversation, he talks about the causes of bone complications in women with breast cancer, and the medications used to address bone metasteses and rapid bone loss.

How can bones be affected by breast cancer?
Well first, cancer that has spread to bone will proceed to destroy the bone. So for women with breast cancer that has spread to bone, this is certainly one important reason for bone loss and subsequent complications.

One of the other problems is aromatase inhibitors, which deprive the body of hormones and which are an effective treatment of breast cancer, can produce an effect that has nothing to do with cancer, but has to do with the metabolism of bone. These medications can produce bone loss and osteoporosis in the same way as in menopause, but they are more dramatic. This is an unfortunate side effect of aromatase inhibitors that we?re becoming more familiar with.

Are there any symptoms of bone metastasis?
Patients who have cancer that has spread to the bone may have no symptoms until the bone lesions become large enough or are placed in such a way that they cause pain. And pain is usually the symptom that a patient first notices. Sometimes a patient may notice weakness in the limb, but they?re weak because when they move the limb, it?s painful. In very advanced cases or if a large lesion has grown rapidly, there can be spontaneous fracture. A patient may have had various aches and pains of no great consequence, and all of a sudden, she has pain all over her chest because she has fractured two or three ribs as a result of the weakening of the bone structure by the cancer which has implanted in there. Women can fracture a hip with minor injuries because the cancer had localized in that region and so forth. So bone fractures can be a sign of advanced disease. But pain is usually the first symptom.
What is actually happening in the bone that initiates bone loss?
Bone is a living tissue. It?s a tissue that heals if it?s injured or fractured, and hurts when it?s injured. There?s blood supply, there are all sorts of things going on, and bone is constantly remodeling itself. Cells called osteoclasts and osteoblasts do this work. The normal function of the osteoclasts is to break down old bone and other cells, and lay down new bone.

So bone loss?whether it happens with menopause or the result of certain hormonal therapies?is a rate of destruction that is not compensated by a rate of production.

Is there anything that can be done to address this bone loss?
Bisphosphonates, which are medications that interfere with the function of the osteoclasts, can stop or slow the action of the osteoclasts in removing bone tissue allowing the bone production to continue. Eventually, the two processes equilibrate, but at least one can stop the process of osteoporosis and bone destruction.


But the role of bisphosphonates may actually be twofold. One is the prevention or hopefully the reversal of the osteoporosis, which can develop as a result of hormone deprivation during hormonal therapy. But bisphosphonates may also protect bone tissue against the damage that can be caused by cancer that has spread to bone.

So these medications may protect against bone metastases?
One of the mechanisms by which bone is destroyed by cancer is, the cancer cell stimulates osteoclasts to destroy more and more bone where the cancer is growing.

We?ve found that by using bisphosphonates in patients who have cancer that has spread to bone, one can slow this process. Bisphosphonates are not specifically an anticancer medication, but they can slow down the destruction of bone, which is stimulated by the presence of the cancer. Bisphosphonates?to some extent, do this.

How are these medications used in women with breast cancer?
Woman receiving hormonal therapy for breast cancer that has spread to bone will also receive bisphosphonates. The combination of bisphosphonates with hormonal therapy is quite common.

Should women without bone metastases who are receiving hormonal therapy take bisphosphonates to prevent bone loss?
Well that poses an interesting question, and one that hasn?t been conclusively answered. We don?t know yet, and large studies are currently underway to determine whether bisphosphonate therapy in postmenopausal women with breast cancer who receive hormonal treatment?usually an aromatase inhibitor?have a lesser incidence of bone metastases or if the appearance of the metastases are delayed. But that will not be known for a number of years.

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