Denosumab also delayed the time to bone radiation by 26 percent compared to zoledronic acid.
And when asked about their quality of life, 10 percent more of those on denosumab had a "meaningful" improvement in quality of life compared to those on zoledronic acid.
The U.S. Food and Drug Administration approved Xgeva, made by California-based Amgen, for preventing bone complications caused by cancer in late 2010. Amgen funded the study. Stopeck, who is also director of the clinical breast cancer program at the University of Arizona's cancer center, has been a consultant and advisor for both Amgen and Novartis, which makes Zometa.
While the researchers say the study provides additional evidence that denosumab outperforms zoledronic acid in this group of patients, Dr. Joanne Mortimer, director of the women's cancer program at the City of Hope Comprehensive Cancer Center in Duarte, Calif., said it is too soon to say one will replace the other.
The downside of zoledronic acid is that patients' kidney function must be monitored and perhaps adjusted before each dose. That's not needed with denosumab.
However, zoledronic acid may have an anti-tumor effect, and it remains in the body longer than denosumab, she said. "And we don't have long-term results from denosumab," Mortimer added.
Cost is another consideration. While denosumab is about $1,650 an injection (plus fees for administering), zoledronic acid costs about $900 to $1,000. Also, zoledronic acid is due to come off patent soon, and should become less expensive.
Mortimer said more research is needed to evaluate which patients benefit from denosumab and zoledronic acid. Currently, "the available guidelines [from the American Society of Clinical Oncology] say to use one or the other," she said.
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