Background: Non-expandable lung (NEL) often complicates management of malignant pleural effusion (MPE). However, its prevalence and clinical impact are poorly understood.

Objectives: Our study aims to describe the prevalence, clinical course and survival impact of NEL in an Asian cohort of MPE.

Methods: Histologically confirmed MPE patients who underwent pleural aspiration or drainage from Jan 2014 to Jan 2020 in a Hong Kong hospital were identified. Serial chest radiographs were evaluated for the presence of NEL (defined as lack of pleural re-apposition after fluid removal) by an independent assessor. Survival was evaluated using Kaplan-Meier curve and multivariate Cox model. 

Results: Of 272 MPE patients with 82% lung cancer primary, 80 (29%) had NEL identified. NEL was more frequently observed in lung cancers (35%) than in other cancer types (6%, p<0.0001), and in large effusion occupying >50% hemithorax (38%) than in smaller effusion (13%, p<0.0001). Patients with NEL had undergone more pleural procedures (median 3, IQR 2-4) compared with those without NEL (median 2, IQR 1-2, p<0.0001). Overall survival time of NEL group was similar to that of non-NEL group (median survival 278 vs 226 days, p=0.42). Using multivariate Cox model, NEL had no independent association with survival (adjusted HR 0.78, 95% CI 0.57-1.06). 

Conclusion: NEL is a relatively common phenomenon in MPE, especially in lung cancer and large effusion, which is associated with more pleural procedures. However, it has no independent association with survival.