Background: ICIs revolutionized aNSCLC treatment. The next challenge lays on the search for predictive markers. Detection of multiple tumor-related genetic alterations through NGS in cell free DNA is a promising tool, provided the limited availability of tumor tissue in most cases. Methods: Between January 2017 and October 2019, aNSCLC pts consecutively referring to our Institution were prospectively screened with plasma NGS while included in two clinical trials: VISION (NCT02864992) and MAGIC trial, an observational study. In VISION trial NGS was performed in plasma (Guardant360 test) and tissue (Oncomine Focus Assay). In MAGIC Myriapod NGS-IL 56G Assay was used. Aim of the study was to evaluate the impact of STK11, KRAS and TP53 mutations (muts) on outcome of ICI-treated pts, with overall survival (OS) as primary endpoint. A control group of pts not receiving ICIs was also analyzed. Results: A total of 235 NSCLC pts were enrolled and received ICIs. 93 pts were analyzed in plasma at the time of beginning ICIs: median OS was 18.9 m (95% CI: 13.7-24.1) and median immune-related progression free disease (irPFS) 3.8 m (95% CI: 2.5-5.1). 49 (52.7%), 22 (23.7%) and 8 (8.6%) pts carried TP53, KRAS and STK11 pathogenic alterations, respectively. STK11 mutated pts showed a trend for worse OS compared with wildtype counterpart (14.9 m, 95% CI: 6.5-23.3, versus 20.3, 95% CI: 13.4-27.2, p = 0.192) KRAS muts had no impact on outcome. Pts with TP53 or STK11/KRAS co-mut (n = 3) had worse OS (12.3 m, 95% CI: 9.2-15.4; HR = 3, 95% CI: 1.6-5.8, p = 0.001 and 5.9 m, 95% CI: 1.4-7.6; HR = 2.9, 95% CI: 1.4-6.3, p = 0.007) and worse irPFS (2.8 m, 95% CI: 1.7-3.9, HR = 1.8 95% CI: 1.1-3.1, p = 0.03 and 1.2 m, 95% CI: 0.9-1.5, HR = 2.2 95% CI: 1.2-4.1, p = 0.01). Number of muts negatively impacts pts’ OS (HR = 1.2, 95% CI: 1.1-1.3, p = 0.02) and was higher among TP53 mutated pts (p < 0.001, Mann-Whitney test). In multivariate analysis, TP53 and STK11/KRAS retained significance. A control group of pts not receiving ICIs was analyzed (n = 101): median OS was 16.8 m (95% CI: 13-20.6). Nor STK11 (n = 10), nor STK11/KRAS (n = 6) had impact on OS (HR = 1.8, 95% CI: 0.7-4.7, p = 0.267 and 1.4, 95% CI: 0.7-3.0, p = 0.293) while the presence of TP53 muts (n = 41) was associated with shorter OS (11.4 m, 95% CI: 7.3-15.5; HR = 2.2, 95% CI: 1.2-4.2, p = 0.009). Conclusions: NGS performed in plasma might be used to detect predictive markers. TP53 muts in plasma at baseline had prognostic value, while STK11/KRAS muts were associated with worse outcome to ICIs.