Randomized controlled trial of pre-transplant zoledronate versus observation for prevention of bone loss in allogeneic hematopoietic cell transplantation.

Background: Approximately half of allogeneic hematopoietic cell transplantation (HCT) recipients experience significant bone loss in the early post-HCT period. Only recently have international guidelines started recommending early screening. However, the guidance for intervention remains conservative. In this study, we sought to evaluate the efficacy of pre-transplant prophylactic zoledronate in preventing early bone loss in allogeneic HCT recipients.

Methods: This was an open-label, investigator-initiated, phase 2 randomized controlled trial (RCT) of prophylactic zoledronate versus observation to prevent bone loss in allogeneic HCT recipients. Recipients aged ≥ 18 years of age were included after informed consent and randomized to prophylactic zoledronate 4 mg pre-HCT or observation in a 1:1 ratio. The primary outcome of the study was bone mineral density (BMD) loss at the femoral neck (FN), total hip (TH), and lumbar spine (LS), as assessed using dual-energy X-ray absorptiometry (DXA) on day+100 post-HCT. The secondary outcomes included BMD loss on day+365 and Z scores on day+100 and day+365 at the FN, TH, and LS sites.

Results: The trial was terminated because the interim analysis showed a significant benefit in the intervention arm, with 50% planned recruitment. A total of 40 patients were randomized to the zoledronate and control arms. Both arms were matched for age, sex, diagnosis, pre-HCT steroid exposure, body mass index, human leukocyte antigen (HLA) match, and conditioning intensity. The grade 2-4 acute graft versus host disease (GVHD) incidences were comparable. The primary endpoint of BMD loss at FN and TH at day+100 was significant (5.62% vs. -6.78%, p = 0.009, -1.59 vs. -3.98, p = 0.016, respectively). There was no difference in the secondary endpoint of BMD loss on day+365 compared to that on day+100 or baseline at any BMD site. There was no difference in the Z-scores at any site on day+100 or day+365.

Conclusions: Prophylactic zoledronate prevented early bone loss on day+100. The indicated preemptive zoledronate beyond day+100 in recipients prevented further bone loss. Patients receiving prophylactic zoledronate may benefit from a supplementary dose of the indicated preemptive zoledronate.