e20550 Background: Soon after the publication of the PACIFIC trial, the Food and Drug Administration (FDA) approved durvalumab following definitive chemoradiation in patients with unresectable stage III non-small cell lung cancer (NSCLC). However, patterns of durvalumab adoption within the United States are currently unknown. We investigated the pace of uptake of durvalumab as well as patient and tumor characteristics associated with receipt of durvalumab following FDA approval. Methods: This study used the nationwide Flatiron Health database, a longitudinal electronic health record-derived de-identified database. During the study period, the de-identified data originated from approximately 280 US cancer clinics (̃800 sites of care). From this de-identified database, we selected patients with stage IIIB-C NSCLC who completed at least two cycles of first-line (1L) platinum doublet chemotherapy between February 16, 2018 (FDA approval date for durvalumab) and August 16, 2019, and did not develop disease progression over a follow-up period of at least 120 days after 1L chemotherapy. In the absence of radiation therapy and surgery details in the database, these criteria served as a proxy for selecting patients who were most likely to be eligible for consolidative durvalumab. We evaluated temporal trends in the uptake of durvalumab after completion of 1L chemotherapy using the Cochran-Armitage test, clustering the time periods in 3-month intervals. We also characterized patient and tumor characteristics associated with durvalumab receipt using the chi-square test and multivariable logistic regression. Results: A total of 424 patients were included in our study sample, among whom 282 (66.5%) patients had documentation of having received durvalumab after 1L chemotherapy. Within the first 3 months after FDA approval, 60.4% of potentially eligible patients received durvalumab, while in the final 3 months of the study period, this proportion rose modestly to 68.3% (p = 0.19). On univariable and multivariable analysis, patient characteristics like age, sex, race, insurance, smoking status, performance status, and comorbidity score, as well as tumor characteristics like histology, EGFR status, and PD-L1 status, were not significantly associated with receipt of durvalumab. However, there was significant geographic variability in receipt of durvalumab, ranging from 65.7% in the South to 85.3% in the Midwest (chi-square p = 0.04). Conclusions: Early adoption of durvalumab upon completion of 1L chemotherapy for stage IIIB-C lung cancer was rapid across the United States, starting at over 60% in the first three months after FDA approval. Regional variation appears to be a more powerful driver than patient characteristics in discrepancies of durvalumab dissemination. Further exploration into these regional variations may help improve guideline-concordant care.