Background: New treatment strategies are needed for advanced NSCLC patients who progress on treatment with immune checkpoint inhibitors (ICI). Tedopi (OSE2101) is a neoepitope vaccine restricted to HLA-A2 positive patients (45%) targeting five tumor-associated antigens frequently expressed in lung cancer cells, ACE, HER2, MAGE2, MAGE3 and P53. Previously, in a phase II trial (Barve et al. JCO 2008), Tedopi showed a median overall survival (OS) of 17.3 months with a manageable safety profile in advanced NSCLC patients. ATALANTE-1 (NCT02654587) is a randomized, open-label, phase 3 study comparing the efficacy and safety of TEDOPI with standard of care (SoC) treatment in HLA-A2 positive patients with advanced NSCLC, as second- or third-line therapy. Methods: Patients with advanced NSCLC without EGFR-sensitizing mutations or ALK rearrangements; progressive disease to platinum-based chemotherapy (ChT) with sequential or concurrent ICI; HLA-A2 positivity (blood test); ECOG PS 0-1; with treated and asymptomatic brain metastases,, are randomized 2:1 to receive 5mg Tedopi subcutaneously Q3W for 6 cycles, then Q8W for the reminder of the year and finally Q12W, or SoC treatment with: docetaxel 75 mg/m² Q3W or pemetrexed 500 mg/m² Q3W (in non-squamous and pemetrexed-naïve patients). Treatment continues until progression, intolerable toxicity or consent withdrawal, in both arms. Patients are stratified by histology, best response to first line, and line rank of ICI. Tumor assessment is performed every 6 weeks (RECIST 1.1). Primary endpoint is OS. Secondary end points are PFS, ORR, DCR, and duration of response, quality of life and safety. This is a superiority study with a hazard ratio of 0.7, two-sided alpha 5% and power 80%, after 278 events are observed. An independent analysis (1year OS rate) is planned in the first 84 patients treated with Tedopi. Last trial review by the DMC in June 18 suggested that the trial continues as planned. Translational research will be performed evaluating pharmacodynamic markers of efficacy such as immunogenicity response against Tedopi vaccine neoantigens, as well as parameters in liquid and tissue biopsies. End January 19, 87 patients (51 Tedopi, 36 Soc) have been enrolled. Clinical trial information: NCT02654587