Clinical and Molecular Features of Malignant Pleural Effusion in Non-Small Cell Lung Cancer (NSCLC) of a Caucasian Population

<b><i>Background and Objectives:</i></b> The diversity of patients with malignant pleural effusion (MPE) due to non-small cell lung cancer (NSCLC) as well as the variability in mutations makes it essential to improve molecular characterization. <b><i>Objective:</i></b> Describe clinical, pathological, and molecular characteristics MPE in a Caucasian population. <b><i>Materials and</i><i>Methods:</i></b> Retrospective study of patients with NSCLC diagnosis who had undergone a molecular study from 1 January 2018-31 December 2022. Univariate analysis was performed to compare patient characteristics between the group with and without MPE and molecular biomarkers. <b><i>Results:</i></b> A total of 400 patients were included; 53% presented any biomarker and 29% had MPE.PDL1, which was the most frequent. EGFR mutation was associated with women (OR:3.873) and lack of smoking (OR:5.105), but not with MPE. Patients with pleural effusion were older and had lower ECOG. There was no significant difference in the presence of any biomarker. We also did not find an association between the presence of specific mutations and MPE (22.4% vs. 18%, <i>p</i> = 0.2), or PDL1 expression (31.9% vs. 35.9%, <i>p</i> = 0.3). Being younger constituted a protective factor for the presence of MPE (OR:0.962; 95% CI 0.939-0.985, <i>p</i> = 0.002), as well as ECOG ≤ 1 (OR:0.539; 95% CI 0.322-0.902, <i>p</i> = 0.01). <b><i>Conclusions:</i></b> This is the first study that describes the clinical, pathological, and molecular characteristics of MPE patients due to NSCLC in a Caucasian population. Although overall we did not find significant differences in the molecular profile between patients with MPE and without effusion, EGFR mutation was associated with a tendency towards pleural progression.