Utility of pleural fluid for predictive marker testing in malignant pleural effusion

Introduction: Pleural fluid cytology has an average diagnostic yield of 60%, depending on cell type. However standard cancer pathways also now require predictive markers (PM) to deliver optimal therapy. Building on an earlier smaller study we set out to determine the utility of pleural fluid cytology for this purpose using data from 4 UK centres. Methods: Electronic data from all patients (Jan 2016-Oct 2018) with pleural fluid cytology samples reporting lung, breast or ovarian cancer were reviewed retrospectively. PM testing was defined as successful if all markers mandated by current ESMO guidelines was completed. Results: 249 patients were identified. Overall, PM testing was successful in 32%, see Figure 1 for details. The median volume of pleural fluid sent in successful cases was 30ml (IQR 20 – 40) vs. 60ml (IQR 25 – 100) in unsuccessful cases (p Conclusions: Testing for PM on pleural fluid is often unsuccessful. ER and PR testing in breast cancer was more successful than average (>80%) but HER2 in breast and BRCA in ovarian cancer was never successful. The time required to report PM and subsequent biopsy will cause treatment delay. A review of pleural diagnostic pathways and a prospective study are warranted.