Women with high-risk, early-stage breast cancer see no improvement in disease-free survival (DFS) or overall survival (OS) after five years of adjuvant bisphosphonate treatment compared with just two years of treatment, according to SUCCESS A, a phase III study. European researchers presented these findings during the San Antonio Breast Cancer Symposium on Wednesday, December 6.

A recent meta-analysis reported benefits of adjuvant bisphosphonate treatment in postmenopausal women with early-stage breast cancer, including improved survival and reduced recurrences in the bone. SUCCESS A trial researchers compared two and five years of zoledronate treatment following adjuvant chemotherapy to assess benefits between durations.

A total of 3,754 women with high-risk, early-stage breast cancer were randomly assigned to adjuvant chemotherapy treatment with three cycles of combination 5-fluorouracil, epirubicin, and cyclophosphamide (FEC) followed by either three cycles of docetaxel or three cycles of gemcitabine plus docetaxel. After chemotherapy, patients were randomly assigned to five years of zoledronate treatment (4 mg IV every three months for two years, followed by 4 mg IV every six months for three years) versus two years of zoledronate treatment (4 mg IV every three months for two years). Outcomes were DFS and OS, with survival times measured between two and four years after zoledronate treatment began. Median observation time was 2.95 years for DFS and 3 years for OS.

Overall, 2,987 of the 3,754 women on study were available for analysis because DFS events or loss to follow up (1,540 women in the five-year zoledronate arm and 1,447 women in the two-year zoledronate arm). DFS and OS did not differ between the two treatment arms (DFS: hazard ratio [HR] = 0.97, 95% CI = 0.75–1.25, p = 0.81; OS: HR = 0.98, 95% CI = 0.67–1.42, p = 0.90). Menopause status also had no impact on DFS of OS; no differences in DFS or OS existed between the two arms in premenopausal (DFS: HR = 1.21, 95% CI = 0.81–1.81, p = 0.35; OS: HR = 0.93, 95% CI = 0.57–1.53, p = 0.78) or postmenopausal women (DFS: HR = 0.85, 95% CI = 0.62–1.16, p = 0.30; OS: HR = 0.96, 95% CI = 0.67–1.39, p = 0.84).

Researchers concluded that extended adjuvant bisphosphonate treatment has no benefit in high-risk women with early-stage breast cancer, regardless of menopause status.