LAUSR

e18593 Background: Bone metastases and skeletal related events (SREs) are a common cause of morbidity among patients with metastatic non-small cell lung cancer (mNSCLC). SREs include pathologic bone fractures, spinal cord compression, orthopedic surgery/stabilization, and palliative radiation to bone. Bone modifying agents (BMA) such as bisphosphonates and RANK ligand inhibitors are often used for mNSCLC patients with bone metastases to reduce the incidence of SRE. Data on the associations between BMA use and overall survival (OS) and the development of SRE among patients with mNSCLC treated with immune checkpoint inhibitors (ICI) is limited. Methods: We conducted a retrospective study of patients with mNSCLC treated with first line pembrolizumab or pembrolizumab plus chemotherapy at The Ohio State University from 2017-2020. The associations between SRE and categorical variables were studied using Fisher’s exact test and with continuous variables using the Kruskal-Wallis test. The association between BMA and risk of osseous progression was studied using Fisher’s exact test. The association between BMA and OS was examined using a Cox proportional hazard model. Median OS was estimated using the Kaplan-Meier method with 95% CI. OS was calculated from date of ICI initiation to death from any cause or last follow up. Results: We identified a cohort of 228 patients: 107 (47%) treated with pembrolizumab and 121 (53%) treated with pembrolizumab plus chemotherapy; 48 (21%) had squamous histology and 179 (79%) had nonsquamous histology (1 had NSCLC histology not specified); median age 62.6 years; median OS was 26.8 months (95% CI: 17.2 – 34.5 months). A total of 95/228 (42%) patients had bone metastases at time of ICI initiation; 45/95 (42%) had treatment with BMA and 50/95 (58%) were not treated with BMA. Among patients with bone metastases at time of ICI, 45 (42%) developed SRE after ICI initiation and BMA use was not associated with risk of SRE (p = 1). BMA use was not significantly associated with risk of osseous progression (p = 0.21). For patients with baseline bone metastases prior to ICI, the use of BMA was not associated with OS (p = 0.24); the type of BMA used (bisphosphonate vs RANK ligand inhibitor) was also not associated with OS (p = 0.13). Conclusions: In patients with metastatic NSCLC treated with first line pembrolizumab alone or with chemotherapy, bone modifying agents were not associated with OS, decreased risk of osseous progression, or development of SRE in patients with baseline bone metastases prior to ICI initiation. The type of BMA used was also not associated with survival. Further studies evaluating the utility and impact of BMA use in this patient population are needed.