Zoledronic acid (ZA) effectively inhibits cancer treatment-induced bone loss (CTIBL) in postmenopausal women (PMW) with early breast cancer (BCa) receiving adjuvant letrozole (Let): 12 mos BMD results of the Z-FAST trial.

533 Background: Aromatase inhibitors (AIs) are effective therapies for PMW with BCa. Their use has been associated with increased bone resorption markers and bone loss at the lumbar spine (LS)/total hip (TH). This multicenter open-label randomized study evaluates the efficacy and safety of ZA in preventing CTIBL in PMW with early BCa who are receiving AI therapy.,602 PMW with stage I-IIIa ER+ and/or PR+ BCa starting Let (2.5 mg qd x 5 yrs) were randomized to upfront ZA (4 mg IV infusion q 6 mos) vs delayed ZA in 93 centers in the US and Canada. The delayed group will receive ZA when either post-baseline T-score decreases <-2 SD or in case of fracture. The primary endpoint is the percent change in LS BMD at 12 mos.,Baseline characteristics were similar between groups. 343 of 602 pts (170 upfront/173 delayed) are evaluable for 12 mos LS BMD. Upfront ZA group shows a mean increase of 2.02% while the delayed group shows a mean decrease of 2.61%, resulting in a significant difference of 4.63% between groups (p<0.001). 347 of 602 pts (175 upfront/172 delayed) are evaluable for 12 mos TH BMD. Upfront ZA group shows a mean increase of 1.40% while the delayed group shows a mean decrease of 2.10%, resulting in a significant difference of 3.50% between groups (p<0.001). Serum markers of bone turnover (N-Telopeptide, Bone-Specific Alkaline Phosphatase) were collected and analyzed on a subset of 226 pts at 3 month intervals for 1 yr. The results showed significant suppression of both markers over 12 mos in favor of upfront vs delayed ZA group. ZA was safe and well tolerated. Updated 12 mos BMD data on all pts will be presented at the meeting.,Upfront ZA prevents CTIBL in PMW with early BCa receiving adjuvant Let at 12 mos. ZA in combination with Let in this setting offers the potential to combine the anti-cancer efficacy of Let with the bone protective effect of ZA. [Table: see text].