[Clinical Characteristics and Prognosis of 76 Lung Adenocarcinoma Patients 
Harboring EGFR Mutations with Pleural Effusion at Initial Diagnosis: 
A Single-center Retrospective Study].

BACKGROUND: Malignant pleural effusion is one of the common clinical manifestations of patients with lung adenocarcinoma. Patients with pleural effusion at the initial diagnosis of lung adenocarcinoma usually indicate poor prognosis. Epidermal growth factor receptor (EGFR) mutations mainly occur in patients with lung adenocarcinoma. Patients with different mutant subtypes have different prognosis. The clinical characteristics and prognostic factors of patients with EGFR mutated lung adenocarcinoma of different molecular subtypes combined with pleural effusion at initial diagnosis are still unclear. This study was designed to explore the clinical characteristics and prognostic factors of these patients in order to provide management recommendations for them. METHODS: A retrospective analysis of the clinical characteristics, treatment, outcomes and progression-free survival (PFS) of first-line treatment in patients with EGFR mutated lung adenocarcinoma combined with pleural effusion at initial diagnosis admitted to Department of Medical Oncology and Radiation Sickness, Peking University Third Hospital from January 2012 to June 2021 was performed. Pearson's chi-square test or Fisher's exact test were performed for comparison between groups. Kaplan-Meier method was performed for survival analysis and Cox proportional risk regression model was performed for multivariate analysis. RESULTS: 76 patients met the inclusion criteria in this study. The incidences of EGFR classical mutations 19del, 21L858R and non-classical mutations were 46.0%, 38.2% and 15.8%, respectively among these patients. There was no significant difference between the three mutations in terms of gender, age, presence of dyspnea at presentation, whether other distant metastases were combined, site of pleural effusion, volume of pleural effusion, presence of other combined effusions, tumor-node-metastasis (TNM) stage, presence of other gene mutations, and treatment of pleural effusion (P>0.05). In patients with EGFR classical mutations 19del or 21L858R or non-classical mutations subtype, the proportion of chemotherapy in first-line regimens were 17.1%, 20.7% and 58.3%, respectively (P=0.001); and first-line disease control rates were 94.3%, 75.9% and 50%, respectively (P=0.003); pleural effusion control rates were 94.3%, 79.3% and 66.7%, respectively (P=0.04); PFS were 287 d, 327 d and 55 d, respectively (P=0.001). Univariate analysis showed that EGFR mutation subtype, control of pleural effusion, first-line treatment agents, and first-line treatment efficacy were significantly associated with PFS (P<0.05). Cox multifactorial analysis showed that only EGFR mutation subtype and first-line treatment efficacy were independent prognostic factors for PFS (P<0.05). CONCLUSIONS: PFS was significantly better for classical mutations than for non-classical mutations in patients with EGFR mutated lung adenocarcinoma combined with pleural effusion at initial diagnosis. Improving the efficacy of first-line therapy is the key to improve the prognosis of these patients.