Accuracy of pleural biopsy for the diagnosis of histologic subtype of malignant pleural mesothelioma: Necropsy-based study of 134 cases

Background: Definition of histologic subtype of malignant pleural mesothelioma (MPM) is important for management of patients, because surgical treatment improves prognosis for patients with epithelioid but not biphasic or sarcomatoid MPM. In a series of necropsies performed in a hospital specialized for MPM diagnosis, we retrospectively investigated the accuracy of histologic diagnosis performed on pathologic specimens collected through pleural biopsies obtained at video-assisted thoracoscopic surgery (VATS) or surgery. Methods: We reviewed histologic records of an unselected series of autopsies performed in patients with MPM employed in the Monfalcone shipyards (Northeast Italy) or living with shipyard workers from 1999 through 2017. Using necropsy results as a gold standard, we calculated sensitivity, specificity, and positive and negative predictive values of histology from VATS or surgery after combining nonepithelioid subtypes. Results: We retrieved necropsy records for 134 patients: 62 (46.3%) with epithelioid, 51 (38.1%) with biphasic, and 21 (15.7%) with sarcomatoid MPM. We observed good sensitivity of VATS (0.94) and surgery (0.89) in diagnosing epithelioid MPM. Conversely, specificity was low (VATS: 0.46; surgery: 0.32). Therefore, positive predictive values were also low (VATS: 0.58; surgery: 0.60). Misclassification was particularly high for biphasic MPM (three-fourths of biphasic MPM at necropsy had been classified as epithelioid at VATS or surgery). Conclusions: We observed a substantial degree of misclassification between epithelioid and biphasic MPM for pleural biopsies performed during VATS. Our results suggest caution should be taken in using histologic subtype obtained from VATS in selecting patients with MPM for surgical treatment. We also observed substantial misclassification of biospecimens collected during MPM surgery.