Introduction and objectivesRecent publications report a significant survival disadvantage associated with minimal pleural effusion (MiniPE) at presentation of non-small cell lung cancer (NSCLC). MiniPE is defined when an effusion is too small for thoracentesis or where aspiration cytology is negative. Occult pleural metastases (OPM), indirect pathophysiology or comorbidity may cause MiniPE, but staging beyond thoracentesis is rarely performed. Assumption of OPM and therapeutic nihilism may contribute to poor outcomes. We assessed the prognostic impact of MiniPE in potentially radically-treatable NSCLC (Stage I-IIIA), oncologists’ attitudes to treatment planning and the final treatment delivered.MethodsElectronic records and baseline imaging were reviewed retrospectively in 441 consecutive diagnoses of NSCLC made over 6 months in 2009. Stage I-IIIA patients were dichotomized into: No effusion and MiniPE. Malignant effusion (Stage IV) cases were recorded for comparison. The impact of effusion status on overall survival (OS) was estimated using Kaplan-Meier methodology. The probable cause of MiniPE was assessed indirectly using follow-up imaging/records. 3 Clinical Oncologists were surveyed for theoretical treatment plans in 8 randomly-selected MiniPE Stage I-IIIA cases based on anonymised imaging and history. These 24 plans were compared to the treatment delivered in MiniPE patients.Results103/441 (23%) patients had MiniPE. 167/441 (38%) were Stage I-IIIA; 26/167 (16%) of these had MiniPE. OS based on effusion status (Stage I-IIIA) is shown in Figure 1. 28/103 (17%) MiniPE patients survived <30 days and had limited post-diagnosis imaging. These were excluded from probable cause analyses. Of the remaining 75/103, 20 (27%) had radiological evidence of progressive pleural malignancy. Radical treatment was delivered in 4/26 (15%) Stage I-IIIA MiniPE cases but advocated in 17/24 (71%) theoretical plans, which showed significant inconsistencies.ConclusionsThese retrospective data confirm the negative prognostic impact of MiniPE and suggest the prevalence of OPM is at least 27% in Stage I-IIIA NSCLC. This is likely an underestimate given our limited data in poor prognosis patients. Radical treatment was rarely delivered despite aggressive treatment plans. A prospective study utilising thoracoscopic staging could define the true prevalence of OPM in MiniPE. Objective staging might improve decision-making, radical treatment rates and OS in this context.Abstract P6 Figure 1Stage I-IIIA NSCLC Survival by Effusion Status

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IntroductionMalignant Pleural Effusion (MPE) is common and often Results in disabling breathlessness. Non-expansile lung (NEL) frequently complicates pleural drainage, resulting in talc pleurodesis failure. Reliable detection of NEL would allow better clinical decision-making and more rational design of MPE trials. We developed 2 semi-objective definitions of NEL, which we hypothesised might prove more accurate and more consistent than the currently used subjective British Thoracic Society (BTS) method.Materials and MethodsA retrospective cohort study was performed, involving 93 consecutive patients who underwent local anaesthetic thoracoscopy at our centre (July 2010- January 2015). NEL was defined prospectively at 3 month follow-up in all. Post-drainage chest radiographs were retrospectively classified as ‘NEL’ or ‘expansile’ by 2 independent assessors using the subjective BTS method and the 2 semi-objective methods (Re-expansion Proportion (REP) and Lateral Apposition Ratio (LAR), shown in figure 1). Sensitivity, Specificity and Inter-observer Agreement (Cohen’s Kappa, k) for NEL by each method were compared. Overall Survival (OS) based on expansion status by each method was compared using Kaplan-Meier methodology (MPE cases only).Results65/93 patients had MPE. Sensitivity (0.81 (95%CI 0.71–0.89)) and specificity (0.87 (95%CI 0.81–1.00)) by the BTS method were highest. REP (sensitivity 0.61 (95%CI 0.49–0.72), specificity 0.94 (95%CI 0.73–1.00)) and LAR (sensitivity 0.56 (95%CI 0.44–0.67), specificity 0.94 (95%CI 0.73–1.00)) were less accurate. Inter-rater agreement (k) for BTS, REP, LAR were 0.68, 0.46 and 0.53, respectively. In MPE patients, NEL was consistently associated with a 2–4-fold lower median OS by all methods.DiscussionThe subjective BTS method appeared more accurate in predicting NEL than REP or LAR in this retrospective study, however all methods were subject to significant inter-observer variation. NEL is strongly associated with mortality. Our data highlight the clinical importance of NEL and its potential impact on MPE trial design, but do not strongly support any of these reported end-points as reliable clinical decision-making tools, trial end-points, or entry/stratification criteria. Further prospective research is needed to standardise the definition of NEL for these purposes, ideally prior to pleural drainage, and link this to patient-centred end-points.Abstract S26 Figure 1Semi-objective definitions of non-expansile lung (NEL) including worked examples and screenshots from Vue PACS v13 (Carestream Health Inc., Rochester, NY).

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