New developments in mesothelial pathology

Abstract

This review article examines some new and some problem areas in mesothelial pathology, four of which are discussed, as follows. (1) The concept of mesothelioma in situ: this lesion is defined as a single layer of bland mesothelial cells without evidence of invasion, but that have lost BAP1 and/or MTAP by immunohistochemistry. Benign reactions can exactly mimic mesothelioma in situ, but a hint to the correct diagnosis is a story of recurrent pleural effusions/ascites of unknown aetiology without radiological or direct visual evidence of tumour. (2) The nature of well‐differentiated papillary mesothelial tumour (WDPMT): WDPMT has a long history of arguments regarding its behaviour, and this uncertainty can now be seen to arise, in part, from the observation that some forms of mesothelioma in situ microscopically look exactly like WDPMT. Hence, it is recommended to always run at least a BAP1 stain on any lesion that looks like WDPMT. Both flat and WDPMT‐like mesothelioma in situ are strongly associated with eventual development of invasive mesothelioma, but this process is relatively slow. (3) New immunostains for separating mesothelioma from other tumours: here, it is proposed that in most cases, and particularly when the differential is epithelioid mesothelioma versus non‐small cell lung cancer, one can make this separation with extremely high sensitivity and specificity using just two stains: HEG1 and claudin‐4. (4) Markers for separating benign from malignant mesothelial proliferations: this topic is briefly reviewed, with an indication of which markers are generally accepted and the best utilisation and possible limitations of each marker.

Single‐incision laparoscopic surgery for benign peritoneal cystic mesothelioma—A Video Vignette

“…Histopathological examination revealed a cystic mesothelial lesion [4,5], and immunohistochemical staining revealed maintained Breast Cancer Type-1 associated protein 1 expression, leading to the diagnosis of benign peritoneal cystic mesothelioma (BPCM) [6,7]. The surgery time was 81 min, with minimal blood loss.…”

“…If conservative management such as manual reduction or hygroscopic dressings fails, surgical repair might be needed. Surgical repair using exploratory laparotomy and stoma revision or relocation of stoma is well known [6][7][8]. Herein, we describe a novel technique for local revision of stoma using linear staplers that avoids laparotomy [9][10][11].…”

BAP1 Loss, Nuclear Grading, and Nonepithelioid Features in the Diagnosis of Mesothelioma in Italy: Nevermore without the Pathology Report

“…The correct recognition and classification of the specific subtype has an important prognostic role [11] and is based on architectural growth patterns, and cytologic, and stromal features often suggestive of the malignant nature of the proliferation. As a second step, the recognition/confirmation of mesothelial origin by immunohistochemistry (IHC) is mandatory [12][13][14]. As guidelines recommend, the use of at least two mesothelial positive markers and two other-nature negative markers guarantees specific differential diagnosis [1].…”

Thoracic tumour pathology

“…The next three articles focus upon pleural tumours. The first of the three, written by Andrew Churg, 13 provides several updates in mesothelial pathology, including the concept of mesothelioma in situ and its differentiation from benign mesothelial proliferations and well-differentiated papillary mesothelial tumour, as well as markers to differentiate mesothelioma from carcinomas and benign mesothelial proliferations. Based on this excellent review, it will become clear to the reader that a minimal panel of claudin 4 and HEG1 immunostains can differentiate epithelioid mesothelioma from carcinomas, in particular NSCLC, with high sensitivity and specificity.…”