Background: Neoadjuvant treatment has demonstrated efficacy in several types of cancer and is increasingly used for the treatment of early-stage cancers with the potential of cancer downstaging to enhance complete surgical resection and to improve clinical outcomes. Recent evidences have demonstrated that the neoadjuvant use of first/second-generation epidermal growth factor receptor (EGFR) tyrosine kinase inhibitors (TKIs) may provide clinically meaningful improvement in EGFRm non-small cell lung cancer (NSCLC) patients, however, limited data were reported on osimertinib, the third-generation EGFR-TKI, in the neoadjuvant setting. Here we present an interim analysis of osimertinib as neoadjuvant treatment for resectable EGFRm NSCLC. Methods: NEOS is a prospective, multi-center, single-arm study to evaluate the efficacy and safety of osimertinib as neoadjuvant treatment in resectable EGFRm (19del/L858R) lung adenocarcinoma. Eligible patients were treated with osimertinib 80 mg orally per day for six weeks followed by surgery. Assessment of response to neoadjuvant therapy was performed according to RECIST 1.1. The primary endpoint was response rate. Secondary endpoints included safety, R0 surgical resection rate, quality of life, major pathologic response (MPR) rate, pathological complete response (pCR) rate, and N2 downstaging rate. Results: As of Dec. 17, 2020, 18 eligible patients (median age 61 [range 46-73], 27.8% male, 22.2% ECOG PS 1) have been enrolled. Patients with clinical stages IIa, IIb, and IIIa (8th AJCC) accounted for 16.7%, 22.2% and 61.1%, respectively. Half (9/18) of the patients had EGFR exon 21 L858R mutations and the other half (9/18) had EGFR exon 19del mutations. Amongst all 15 patients who completed efficacy assessment after neoadjuvant osimertinib, the response rate (RR) was 73.3% (11/15) and the disease control rate (DCR) was 100% (15/15). R0 surgical resection was performed in 93.3% (14/15) patients. Pathological downstaging occurred in 53.3% (8/15) patients. 42.9% (3/7) of the patients with confirmed N2 lymph nodes experienced downstaging to N0 disease after receiving neoadjuvant osimertinib. One patient was identified with a pCR. Adverse events (AEs) were reported in 66.7% (12/18) of patients, with the most common AE being rash (8/18, 44.4%), oral ulceration (8/18, 44.4%), and diarrhea (5/18, 27.8%). No grade 3-5 AEs or serious AEs were reported. Conclusions: Interim analysis from this study indicated neoadjuvant osimertinib as an effective and feasible treatment in patients with resectable stage II-IIIB EGFRm NSCLC. The trial is ongoing and the final results will be provided in the future. Clinical trial information: ChiCTR1800016948.