Is Early Injection-Site Reaction Associated With the Efficacy of Romosozumab?

Introduction Injection-site reactions (ISRs) associated with romosozumab may indicate immune activation that influences bone mineral density (BMD) response, aligning with the concept of "immunoporosis." This study aimed to investigate whether early ISRs following romosozumab administration are associated with greater increases in BMD in women with primary osteoporosis. Methods We conducted a sub-analysis of a previously reported prospective cohort study involving 181 untreated Japanese women aged 52-100 years with primary osteoporosis who began a 12-month course of romosozumab. Patients were categorized into an ISR group (n=44) and a non-ISR group (n=137) based on the occurrence of ISRs within the first six months of treatment. Percent changes in lumbar spine (LS), total hip (TH), and femoral neck (FN) BMD at six and 12 months were compared between groups using Student's t-test or Fisher's exact test. Results The ISR group exhibited significantly greater increases in LS BMD compared to the non-ISR group at six months (12.8% vs. 9.5%, p=0.039) and 12 months (18.0% vs. 14.4%, p=0.046). In contrast, no significant differences were detected between groups in TH BMD at six months (3.5% vs. 2.9%, p=0.647) or 12 months (6.7% vs. 5.5%, p=0.330), or in FN BMD at six months (4.0% vs. 3.5%, p=0.588) or 12 months (6.7% vs. 5.4%, p=0.326). Conclusion ISR could serve as a no-cost and clinically observable indicator associated with LS BMD response to romosozumab that requires no additional testing. Further studies are needed to validate this hypothesis and clarify the underlying mechanisms.