e20007 Background: Epidermal Growth Factor Receptor mutations ( EGFRm) are commonly found in patients with resectable and metastatic non-small cell lung cancer (NSCLC). In December 2020, the FDA approved adjuvant osimertinib, for resectable EGFRm NSCLC, based on results of the ADAURA trial which showed significant survival benefit compared to placebo post-resection, further reinforcing need for biomarker testing in NSCLC. In light of publication of Aduara this study aims to understand US oncologists' biomarker testing practices and adjuvant osimertinib use in resectable EGFRm Stage IB–IIIA NSCLC. Methods: Questions related to biomarker testing and adjuvant therapy decision-making for resectable EGFRm Stage IB–IIIA NSCLC were presented to US-based oncologists/hematologists during live meetings in June and July 2023. In addition, questions related to impact of updated overall survival data from ADAURA trial on physicians’ reported treatment preferences were presented.Up to 108 participants responded to questions, though not all participants answered each question. Aggregate responses were summarized using descriptive statistics. Results: Among respondents, 52% identified as medical oncologists and 46% as hematological oncologists, 41% identified as being from an independent community practice and 75% indicated lung cancer was among the 3 solid tumors they most often treat. For patients with newly diagnosed resectable NSCLC patients, respondents indicated that genetic testing was performed before surgery on initial diagnostic biopsy sample (73%), after surgery (44%), and upon progression/relapse (31%). Commonly utilized diagnostic tools reported by respondents included NGS testing of tissue samples (87%), NGS liquid biopsy (42%), and IHC (31%). Barriers impacting molecular testing practices for resectable NSCLC included access to tissue for testing, cost to patient, disease stage, histology, tumor burden, patient age, patient fitness, and prior authorization or time to approval. Half (50%) of respondents reported prescribing adjuvant osimertinib monotherapy for patients with resectable EGFRm NSCLC in the past 6 months. After reviewing the updated ADAURA data, most (83%) respondents indicated they would prescribe adjuvant osimertinib immediately following surgery for resectable EGFRm NSCLC, and 56% would prescribe adjuvant osimertinib with or without adjuvant chemotherapy, 21% would prescribe adjuvant osimertinib with adjuvant chemotherapy, and 17% would prescribe adjuvant osimertinib only. Conclusions: Overall, nearly three-fourths of medical oncologist respondents prefer pre-operative genetic testing and regardless of test timing, when EGFRm identified > 80% will treat adjuvantly with osimertinib. Unfortunately, multiple barriers complicate this pursuit of evidence-based medicine.