Pleural effusions associated with squamous cell lung carcinoma have a low diagnostic yield and a poor prognosis

Background: Malignant pleural effusion (MPE) portends a poor prognosis in non-small cell lung cancer (NSCLC). However, the yield of pleural fluid cytology as well as survival of patients with MPE associated with squamous cell carcinoma versus adenocarcinoma is not well understood. We conducted this study to assess the diagnostic yield of pleural cytology and survival of patients with NSCLC related MPE.

Methods: We performed a single-center, retrospective analysis of patients with NSCLC related MPE between 2010 and 2017. Kaplan-Meier method was used to compare survival and Cox proportional hazards analysis to assess if squamous cell cytopathology was associated with mortality.

Results: We identified 277 patients, 29 with squamous cell and 248 with adenocarcinoma MPE. Pleural fluid cytology from initial thoracentesis was diagnostic in 13.8% (4/29) patients with squamous cell and 80.2% (199/248) with adenocarcinoma (P<0.001). Cytology from second thoracentesis was diagnostic in 13.3% (2/15) patients with squamous cell carcinoma, compared to 37.5% (12/32) with adenocarcinoma (P=0.17). There was no statistically significant difference in the pleural biopsy yield from medical pleuroscopy or video-assisted thoracoscopic surgery (VATS) in the two groups. The median survival of patients with squamous cell MPE was 112 [interquartile range (IQR): 44-220] days versus 194 (IQR: 54-523) days in adenocarcinoma (Log-rank test P=0.04). Multivariate Cox proportional hazards analysis showed that squamous cell cytopathology was independent predictor of mortality (hazard ratio for death of 1.73, 95% CI: 1.1-2.6; P=0.01).

Conclusions: Pleural fluid cytology has a low diagnostic yield in squamous cell carcinoma MPE, and these patients have a poor survival compared to lung adenocarcinoma.