progression-free survival (PFS). The immunostimulatory effects of SBRT and potential synergy with immune checkpoint inhibitors has prompted enthusiasm in combining the two; however, the toxicity is unknown. Method: In this phase Ib study, a cohort of 21 pts with oligometastatic NSCLC receive SBRT to all sites of disease between 30 and 50 Gy in five fractions and durvalumab 1500 mg IV + tremelimumab 75 mg IV every 4 weeks x 4 cycles in a sequential fashion, followed by durvalumab maintenance until progression, unacceptable toxicity or patient wishes. Eligible patients had 1-6 metastatic extracranial lesions, all of which were suitable for SBRT, ECOG performance status 0-1, no actionable driver mutation, and no prior immunotherapy.The primary endpoint is safety of this combination. The period for evaluating dose-limiting toxicities (DLTs) is from the time of first administration of SBRT until 28 days post completion of the first dose of durvalumab and tremelimumab. Grading of DLTs follows CTCAE version 4.03. A DLT will be defined as any Grade 3 toxicity. Secondary endpoints include PFS and overall survival. Correlative studies of baseline TMB, PD-L1 expression on post-SBRT biopsy and immune biomarkers on circulating tumor cells will be correlated with outcomes. In this interim analysis, we assess the safety of the first nine patients enrolled. Result: Nine pts enrolled from 2/2018-3/2019. Median follow-up: 2.8 months (range 1.5-8.2 months). Characteristics included: median age 72 years (range 56-81 years), female/male 2/7, squamous/ nonsquamous 2/7, median number of sites treated 2, CNS involvement 3/9. Most toxicities were Grade (G) 1/ 2. Severe adverse events (AEs) included: G4 elevated CK (1). Severe immune-related (ir)AEs: G3 rash (1), G3 AST (2), G3 ALT (1), G3 amylase (1), G3 lipase (1). One DLT reported due to grade 3 AST > 7 days (recovered). One additional pt discontinued treatment due to grade 3 irAE. There were no treatmentrelated deaths. Two patients (22%) died of disease progression. Conclusion: There were no unexpected safety signals in the first nine patients enrolled. The incidence of grade 3 or greater irAEs was similar to those seen in the treatment of advanced NSCLC, and no additional toxicity is observed with the addition of SBRT to date. The study continues to enroll and results will be updated.

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Conclusion: Current work-up without invasive tools for cN2a in AP zone showed relatively high false-positive rate (32.1%). However, surgical outcome of cN2a in aortopulmonary zone was comparable. Upfront surgery should be considered in highly selected patients.