Adjuvant zoledronic acid may aid breast ca survival.(NEWS)

SAN ANTONIO--The number of premenopausal women with hormone-responsive early breast cancer who need to be treated with zoledronic acid for 3 years to prevent one cancer-related major event in 4 years is 31, according to a large Austrian study.

As numbers-needed-to-treat (NNT) go, an NNT of 31 is favorable. Indeed, it's comparable to the NNTs associated with other major therapeutic advances that have transformed adjuvant therapy for premenopausal breast cancer, such as the taxanes, study investigator Dr. Michael Gnant asserted at the San Antonio Breast Cancer Symposium.

He presented a new secondary analysis from the Austrian Breast and Colorectal Study Group trial 12 (ABCSG-12), which involved 1,803 premenopausal patients with hormone-responsive early breast cancer who were undergoing ovarian suppression with the gonadotropin-releasing hormone analogue goserelin.

Participants were randomized to 3 years of endocrine therapy with either tamoxifen or anastrozole (Arimidex), and further randomized to receive 4 mg of intravenous zoledronic acid (Zometa) every 6 months or not.

Treatment with anastrozole did not result in significantly different disease-free survival, compared with tamoxifen. The addition of zoledronic acid to either endocrine therapy did, however, result in a highly significant 36% improvement in disease-free survival. The combined end point of local recurrence, contralateral breast cancer, distant metastasis, secondary carcinoma, or death occurred in 54 patients in the zoledronic acid arm, compared with 82 who didn't receive the bisphosphonate, according to Dr. Gnant, professor of surgery at the Medical University of Vienna.

There were 16 deaths in the zoledronic acid arm and 26 in the control group, a 40% relative risk reduction that didn't achieve significance, he added.

Dr. Gnant noted that an Italian National Cancer Institute meta-analysis of phase III trials of adjuvant taxane therapy in early breast cancer found that the NNT "with 43-60 months of docetaxel to prevent one event included in disease-free survival was 31, identical to the NNT for zoledronic acid in the ABCSG-12 trial. The NNT for 60-69 months of adjuvant paclitaxel was 28 in the Italian study (Cancer 2006;106:2337-44).