Accuracy of pleural fluid cytology in patients with malignant pleural effusion from non-small-cell lung cancer, pulmonary metastases and pleural mesothelioma. A case-control study

Background: The usefulness of pleural fluid cytology (PFC) in patients with malignant pleural effusion (MPE) is controversial, and the reported overall sensitivity varies widely, according to the different causes of MPE. This study retrospectively compared the results of PFC performed in a group of patients with confirmed pulmonary or pleural malignancy, and evaluated whether this technique might help to establish the etiology of the effusion. Methods: Medical records from 117 consecutive patients with confirmed lung or pleural malignancy and MPE who underwent PFC (cases) were reviewed. There were 66 (56.4%) men and 51 (43.6%) women with a median age of 70 years (range 40-88 years). Controls were 58 patients with benign pleural effusion. Final pathology showed 48 (41.0%) non-small-cell lung cancer (NSCLC), 38 (32.5%) pulmonary metastases (PMs) from colorectal and non-colorectal cancer, and 31 (26.5%) pleural mesotheliomas (MT). Results: Overall, the sensitivity of PFC was 57.3% and the specificity 98.3%. The other results are reported in the Table. The presence of atypical reactive mesothelial cells, suspicious for malignancy, was considered as a false positive result. The sensitivity of PFC in detecting NSCLC, PMs, and MT was 60.4%, 71.0%, and 42.1%, respectively. PFC was significantly more sensitive in patients with PMs with respect to those with MT (Χ2=5.75, OR=0.30, 95%CI=0.11-0.81, p=0.016), while the difference was not significant between NSCLC and both MT (Χ2=0.92, OR=0.62, 95%CI=0.24-1.64, p=0.33) and PMs (Χ2 =2.85, OR=0.48, 95%CI=0.20-1.13, p=0.09). Conclusions: Pleural fluid cytology is an inexpensive diagnostic tool that should be routinely performed in all patients with MPE, having virtually 100% specificity.