Nancy A. Melville

October 08, 2013

BALTIMORE — The oral bisphosphonate risedronate can maintain or even improve skeletal strength among postmenopausal women experiencing bone loss due to breast-cancer treatment with aromatase inhibitors, according to new results from a 2-year trial presented at the American Society for Bone and Mineral Research (ASBMR) 2013 Annual Meeting.

The research is some of the first to examine the impact of an oral bisphosphonate in such women with low bone mass rather than overt osteoporosis, said Susan Greenspan, MD, a professor of medicine and director of the Osteoporosis Prevention and Treatment Center at the University of Pittsburgh Medical Center, Pennsylvania, who reported the findings.

The study is also novel because it looked at the use of 3 aromatase inhibitors, an important practical point because people often switch between different drugs in this class, Dr. Greenspan told Medscape Medical News.

The findings suggest that the benefits of bisphosphonate treatment in those with breast cancer appear similar to those seen in the general population.

"We were encouraged to see that the improvement was what might be expected among women not taking any breast-cancer therapy," said Dr. Greenspan. "The bone density actually improved in the spine and the femoral neck despite the use of an aromatase inhibitor, while in the placebo group the measures declined."

Suzanne Jan De Beur, MD, an associate professor of medicine at Johns Hopkins University School of Medicine, Baltimore, Maryland, and moderator of the session in which the results were presented, said the study was "well-done" and the data "compelling," offering valuable insights on a useful option for preventing bone loss in breast-cancer patients. While intravenous bisphosphonates are commonly used in such patients, Dr. De Beur said oral formulations offer patients another choice, so "it was good to see that an oral bisphosphonate can be effective."

Bone Loss Accelerated in Women Taking Aromatase Inhibitors

Bone loss is accelerated in women taking aromatase inhibitors due to the drugs' inhibition of the peripheral conversion of androgens to estrogen, Dr. Greenspan explained.

For the current study, the Risedronate's Effect on Bone in Women With Breast Cancer II (REBBeCA II) trial, 109 breast-cancer survivors with a mean age of 64.2 years with low bone mass and taking aromatase inhibitors were randomized to risedronate 35 mg once weekly or placebo for 2 years.

The subjects in both groups also received daily calcium supplementation up to 1200 mg and 800-IU vitamin D, so there were no differences in calcium/vitamin-D intake, nor were there significant differences between the 2 study groups in terms of age, body mass index (BMI), or bone-mineral density (BMD).

Among the participants, 77% were taking anastrozole (Arimidex, AstraZeneca), 15% were taking letrozole (Femara, Novartis), and 8% were on exemestane (Aromasin, Pfizer).

With 87% completing the study at 2 years, significant increases in BMD at the spine, total hip, and femoral neck were seen in the active-treatment group compared with the placebo group at 1 and 2 years.

The treatment group showed an absolute difference of 3.9 percentage points at the spine and 3.2 at the total hip at 24 months.

Dr. Greenspan said the improvements were important, considering the significant bone loss associated with aromatase-inhibitor treatment.

"In women in this age group (mid-60s), bone loss is typically about 1% per year, but women on aromatase inhibitors lose about 2.6% per year," she said.

There were no significant differences in side effects between the 2 groups, and the medication was well-tolerated.

Good to Have an Oral Option

Clinical guidelines from the American Society of Clinical Oncologists (ASCO) recommend that women being treated for breast cancer are considered for antiresorptive therapy, and Dr. Greenspan said the new findings underscore that women with low bone mass can benefit from bisphosphonate treatment when also receiving treatment for breast cancer.

She added that it was important to evaluate an oral bisphosphonate, because many women are reluctant to have an injection. Also, "If there are side effects and it's just a once-a-week therapy, they will be gone relatively soon, compared with an intravenous treatment, which is in the bloodstream and can last much longer.

"Aromatase inhibitors have become the standard of care for breast cancer, but we know these patients will lose bone, and this study lets us know that the bisphosphonate risedronate can prevent it and seems to be safe and effective," she concluded.

Dr. De Beur said oncologists often use IV bisphosphonates, such as zoledronic acid, which are more potent, so "it was encouraging to see that the bone density…went up and that [it] can be improved" with an oral bisphosphonate in women taking aromatase inhibitors.

Another benefit of oral formulations "is that if the patient…for some reason stops taking [aromatase inhibitors] after only 6 months or so, you can stop the bisphosphonates as well at that point, so it's nice to be able to have choices for women.

"I think the study offers information that can drive a change in our clinical practice," she concluded.

Dr. Greenspan and Dr. De Beur have reported no financial relationships.

American Society for Bone and Mineral Research 2013 Annual Meeting. Abstract 1050, presented October 6, 2013.

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