Abstract
9005 Background: ZOL (4 mg q 4 wk) is an established therapy for reducing the risk of debilitating skeletal-related events (SREs) in patients (pts) with bone metastases (mets) from BC. As BC treatments continue to improve pt survival, long-term SRE-reduction is increasingly important, and evaluation of modified ZOL dosing to retain efficacy with reduced adverse events (AEs) is warranted. Methods: ZOOM, a phase III prospective, randomized, open-label, multicenter study, assessed the safety and efficacy of quarterly (4 mg q 12 wk; Arm 1) vs monthly (4 mg q 4 wk; Arm 2) ZOL for ~1 yr in pts with BC who have ≥ 1 bone met, and have received ~1 yr of prior ZOL treatment (9 to 12 doses over ≤ 15 months; last dose ≤ 3 months prior). The primary endpoint was skeletal morbidity rate (SMR; number of SREs/pt/yr). Sample size to detect non-inferiority with 80% power (1-sided a = 0.025) was 420 pts. Secondary endpoints included time to first SRE, bone pain, bone marker (N-telopeptide of type I collagen; NTX) levels, and safety. Results: 425 pts were enrolled (209 in Arm 1; 216 in Arm 2); arms were well balanced for pt and disease characteristics, and anticancer therapies. SMR was similar between arms: 0.26 (95% confidence interval [CI] = 0.15, 0.37) in Arm 1 vs 0.22 (95% CI = 0.14, 0.29) in Arm 2; between-arms difference = 0.04 (upper limit of 1-tailed 97.5% CI = 0.17). Despite the proximity of 0.17 to the adjusted non-inferiority margin (0.19), the non-inferiority of Arm 1 vs 2 remains statistically significant. Safety analyses showed that ZOL was well tolerated. Renal AEs were reported in similar proportions of pts in both arms; 7 cases of osteonecrosis of the jaw were reported (1.65% overall; 4 cases in Arm 1 vs 3 in Arm 2). Conclusions: ZOOM is the first randomized trial to compare ZOL q 12 wk vs ZOL q 4 wk in BC pts after 1 yr of standard ZOL therapy. SMR was similar between arms. Limitations in study design suggest the need to confirm non-inferiority of ZOL q 12 wk in other ongoing phase III trials.
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