Background: Infections are common complications in patients with non-small cell lung cancer (NSCLC) and may adversely influence clinical outcomes. Their prognostic impact after definitive treatment is not well established. This study aimed to investigate the incidence, microbiological profile, and prognostic significance of infections occurring within one year after definitive treatment in patients with NSCLC. Methods: We retrospectively analyzed patients with NSCLC who completed definitive treatment between 1 January 2016, and 31 December 2023. Microbiological culture results obtained within one-year post-treatment and inflammatory markers measured one month after treatment were evaluated. Pathogens were classified as healthcare-associated infection (HAI) or non-HAI agents. Overall survival (OS) was estimated using the Kaplan–Meier method, and prognostic factors were assessed using Cox regression analysis. Results: Among 214 eligible patients, 45 had positive microbiological cultures. Gram-negative bacteria predominated (n = 24), with Pseudomonas aeruginosa (n = 8) and Acinetobacter baumannii (n = 6) being the most frequently isolated species. Among all isolates, 20 Gram-negative and 6 Gram-positive microorganisms were identified as HAI pathogens. In multivariate analysis, culture positivity (HR: 2.75, p < 0.001) remained an independent prognostic factor for worse OS. Conclusion: Infections within the first year after definitive treatment, particularly those caused by HAI-related Gram-negative pathogens, are associated with reduced OS in NSCLC. Early microbiological diagnosis, targeted antimicrobial therapy, and strict infection prevention strategies may help improve outcomes in this high-risk population.

Infections arising after radiotherapy for glioblastoma are insufficiently characterized. We aimed primarily to describe the microbiological profile and ant