Wednesday: Medical Research Study

Newer Bone Drug Better for Advanced Breast Cancer Patients: Study

But expert says it's too soon to say it will replace older drug.

The relatively new drug denosumab (Xgeva) reduces bone complications of advanced breast cancer more effectively than another osteoporosis drug, zoledronic acid (Zometa), according to new research.

Zoledronic acid belongs to a class of drugs known as bisphosphonates, which help delay bone complications such as fractures, spinal cord compression and bone pain. But zoledronic acid has been linked with kidney toxicity and other reactions. Denosumab, a newer drug called a monoclonal antibody, is superior to zoledronic acid in reducing skeletal problems and better tolerated, the study found.

"It's more effective at preventing bone destruction caused by breast cancer that has spread to the bone," said Dr. Alison Stopeck, associate professor of medicine at the University of Arizona, Tucson, and an investigator on the study, which was published Aug. 14 in the journal Clinical Cancer Research.

When cancer cells from the breast move to the bone, they stimulate osteoclasts, cells that break down bone tissue. In the face of severe bone pain, doctors resort to radiation therapy. "The most common reason for radiation therapy [in these patients] is bone pain," Stopeck said. The radiation kills the tumor cells, and the osteoclasts aren't stimulated, she explained.

Following up on previous research, the researchers assessed bone complications, health-related quality of life and length of time to radiation therapy in more than 2,000 women with breast cancer that had metastasized, or spread, to the bone.

The investigators assigned half of the women to denosumab, which is given by injection, and the others to zoledronic acid, given intravenously. Both drugs were given once a month for 20 months.

Denosumab was a bit better on all counts, they found.

Thirty-one percent of denosumab patients had a skeletal complication compared to 36 percent of the zoledronic acid patients.

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.

More information

To learn more about cancer's spread, visit the U.S. National Cancer Institute .

(SOURCES: Alison Stopeck, M.D., associate professor of medicine, and director, clinical breast cancer program, Arizona Cancer Center, University of Arizona, Tucson; Joanne Mortimer, M.D., director, Women's Cancer Program, City of Hope Comprehensive Cancer Center, Duarte, Calif.; Aug. 14, 2012, Clinical Cancer Research )