The addition of zoledronic acid (ZometaR) to adjuvant endocrine therapy in premenopausal women with early breast cancer significantly reduces the risk of disease-free and recurrence-free survival events by about a third, according to results released at the 33rd Annual Congress of the European Society of Medical Oncology (ESMO.

The data are from the landmark phase III Austrian Breast & Colorectal Cancer Study Group Trial 12 (ABCSG-12) study, which found in an earlier analysis that zoledronic acid plus routine endocrine therapy sustained bone mineral density (BMD) during three years of endrocrine therapy and actually improved BMD two years after the completion of therapy.

Michael Gnant, MD, with the Medical University of Vienna (Austria) and colleagues elsewhere, randomized 1,803 premenopausal 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.

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

The earlier analysis did not assess the impact of specific factors such as tumor stage, tumor grade, lymph node involvement and progesterone receptor status on outcomes in the different treatment groups.

The present analysis showed that zoledronic acid plus endocrine therapy yielded a 33% reduction in the risk of disease-free survival events (p=0.02) and recurrence-free survival events by 32% (p=0.03) versus endocrine therapy alone.

Elsewhere at the meeting, investigators reported that results from the Z-FAST/ZO-FAST trial showing that upfront treatment with zoledronic acid is better than delayed treatment for decreasing aromatase inhibitor-associated bone loss in premenopausal women with early breast cancer who received letrozole after surgery. Overall, 3.6% of women who received upfront zoledronic acid developed recurrent disease versus 5.5% of women who started zoledronic acid after the onset of bone loss, p=.0183.

Finally, preliminary results of an ongoing study suggest that zoledronic acid decreases the prevalence of disseminated tumor cells in the bone marrow in women with early breast cancer.

“Overall, the results from the three studies add to the growing body of evidence in support of an anticancer effect for zoledronic acid,” Diane Young, MD, Head of Global Medical Affairs at Novartis Oncology, pointed out.

Written by Jill Stein
Jill Stein is a Paris-based freelance medical writer.