Adding zoledronic acid to breast cancer therapy improves outcomes

STOCKHOLM (Reuters Health) - Treatment with the bisphosphonate zoledronic acid along with adjuvant endocrine therapy significantly improves clinical outcomes in premenopausal women with early breast cancer, investigators reported at the 33rd Congress of the European Society for Medical Oncology (ESMO).

The results show that, compared with endocrine therapy alone, combined treatment cuts recurrence or relapse by more than a third. "The magnitude of the treatment effect is larger than that typically seen with new chemotherapy agents," said principal investigator Dr. Michael Gnant, with the Medical University of Vienna, Austria.

Dr. Gnant and colleagues randomized 1,803 women to three years of treatment with either goserelin plus tamoxifen with or without zoledronic acid or goserelin plus anastrozole with or without zoledronic acid as part of the phase III Austrian Breast & Colorectal Cancer Study Group Trial 12 (ABCSG-12) study.

All participants in the trial were premenopausal and had estrogen receptor-positive stage I or II breast cancer with fewer than ten positive nodes.

The primary endpoint in the analysis was disease-free survival (DFS) at five years in the tamoxifen versus anastrozole group and the zoledronic acid versus no-zoledronic acid group.

Results showed that zoledronic acid plus endocrine therapy yielded a 36% reduction in the risk of DFS events versus endocrine therapy alone (p = 0.012).

The treatment also improved recurrence-free survival (RFS), a secondary endpoint, with a reduction in risk of RFS events of 35% (p = 0.014).

In addition, zoledronic acid produced a trend towards improved survival (p = 0.10) and a trend towards a reduction in bone metastases (p = 0.22).

The study also documented a decrease in contralateral breast cancer, locoregional recurrences, and distant recurrences with zoledronic treatment. "This shows us that the drug is not only affecting bone but also impacting indirectly on the 'silent fights' between the patients and their dormant tumor cells," Dr. Gnant observed.

The combination of zoledronic acid and adjuvant endocrine therapy was generally well tolerated.

"What's great is that we can eliminate more than a third of relapses by using a low-intensity treatment requiring only two 15-minute infusions per year at six-month intervals for a total of seven infusions," Dr. Gnant, professor of surgery, said. "So this means that treatment is done in about three years."

He estimated that about half of all breast cancer patients under 55 years of age could benefit from zoledronic acid treatment.

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