Denosumab Slightly Better Than Zometa at Easing Bone Pain, Complications of Metastatic Breast Cancer

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Metastatic breast cancer that has spread to one or more bones can be painful and can cause broken bones and spinal compression if bone is destroyed by the cancer. Zometa (chemical name: zoledronic acid) is used to strengthen bones in women diagnosed with breast cancer that has spread to the bone. Zometa is given intravenously and can reduce bone pain and the risk of fractures and other bone complications.

A study found that denosumab, an experimental targeted therapy medicine, was a little better than Zometa at preventing bone pain and slowing bone complications, including broken bones, from breast cancer that had spread to the bones. These results were reported at the 2009 San Antonio Breast Cancer Symposium.

Targeted therapy medicines target specific cell characteristics that affect how the cells behave. Some targeted therapies, including denosumab, are antibodies that work like the antibodies made naturally by the body's immune system. Denosumab targets a protein called RANK ligand (RANKL), which affects the activity of certain bone cells (osteoclasts). Osteoclasts cause a normal amount of bone breakdown to help regulate the body's calcium level. Osteoclasts tend to be overactive when breast cancer spreads to the bones. Overactive osteoclasts can cause bone pain and bone destruction. By blocking or inhibiting the RANKL protein, denosumab lowers the activity level of the osteoclasts, which reduces the risk of pain and other bone complications.

In this study, 2,046 women diagnosed with advanced-stage breast cancer that had spread to bone were split into two groups:

  • about half the women got denosumab every 4 weeks; denosumab is given as an injection under the skin
  • the other women got Zometa every 4 weeks; Zometa is given intravenously every 4 weeks

To make sure that neither the doctors nor the women knew who was getting which medicine, all the women got both an injection and an intravenous infusion, one of which had no medicine in it, every 4 weeks.

All the women were monitored for bone pain, bone fractures, and spinal cord compression. The researchers also watched to see if any of the women needed radiation treatments or surgery to treat bone complications due to the cancer.

  • The length of time before moderate or severe bone pain developed was 13% longer in women who received denosumab compared to women who got Zometa.
  • Radiation often is used to treat bone pain caused by metastatic breast cancer; women who got denosumab went about 22% longer before they needed radiation treatment compared to women who got Zometa.
  • Bone complications (also called skeletal morbidities) -- fractures, spinal cord compression, or the need for radiation or surgery to bone metastasis problems -- were 22% lower overall in women who got denosumab compared to women who got Zometa.
  • Bone complications happened a little bit later in women who got denosumab compared to women who got Zometa, but this difference wasn't statistically significant, which means it could have been due to chance and not because of the denosumab.

Denosumab seemed to cause the same side effects as Zometa. A rare but serious side effect of both medicines is osteonecrosis of the jaw, a condition in which the cells in the jawbone start to die. Osteonecrosis of the jaw developed in 1.4% of women who got Zometa and 2% of women who got denosumab.

While these results are promising, denosumab is still considered an experimental treatment. The U.S. Food and Drug Administration (FDA) is considering approving denosumab to treat women diagnosed with breast cancer that has spread to bone. One advantage of denosumab is that it's given by a simple injection under the skin, instead of an intravenous infusion like Zometa. Still, denosumab is expected to be more expensive than Zometa.

If you've been diagnosed with advanced-stage breast cancer that has spread to one or more of your bones, you and your doctor will work together to develop a treatment plan that minimizes any pain you might have and reduces your risk of bone complications. Zometa may be part of your plan, but if denosumab is approved by the FDA, it could be an option.

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