CD146 immunohistochemical staining for the separation of benign from malignant mesothelial proliferations

Concordance between CDKN2A homozygous deletion and MTAP immunohistochemical loss in fluoroedenite-induced pleural mesothelioma: An immunohistochemical and molecular study on a single-institution series

Fluoroedenite-induced pleural mesothelioma (FE-induced-PM) is a rare and small subset of PM that shares with its asbestos-induced counterpart the same aggressive biological behavior and poor prognosis, but that differs from it from a pathogenetic point of view as it is associated with exposure to fluoroedenite, a carcinogenic agent that shows similarities with tremolite amphibolic asbestos fibers. Although it has been demonstrated that asbestos-induced PMs frequently harbor CDKN2A homozygous deletion and that the immunohistochemical loss of MTAP may represent a cheap and reliable surrogate marker for this molecular alteration, little is known about the molecular landscape and the reliability of MTAP immunohistochemistry in this peculiar subset of PM. The study herein presented investigated the prevalence of CDKN2A homozygous deletion and its concordance with MTAP immunohistochemical status on a cohort of 10 cases of FE-induced-PM from patients with environmental exposure to FE fibers, who were residents in the small town of Biancavilla (Sicily, Italy) or nearby areas. CDKN2A homozygous deletions were found in 3 out of 10 cases (30%) and all these cases showed concomitant cytoplasmic loss of MTAP with a concordance rate of 100%. Despite the relatively low number of cases included in our series, MTAP immunohistochemistry seemed to represent a reliable immunohistochemical surrogate marker of CDKNA homozygous deletion even in this subset of PMs.

High sensitivity flow cytometry immunophenotyping increases the diagnostic yield of malignant pleural effusions

Diagnosing malignant pleural effusions (MPE) is challenging when patients lack a history of cancer and cytopathology does not detect malignant cells in pleural effusions (PE). We investigated whether a systematic analysis of PE by flow cytometry immunophenotyping (FCI) had any impact on the diagnostic yield of MPE. Over 7 years, 570 samples from patients with clinical suspicion of MPE were submitted for the FCI study. To screen for epithelial malignancies, a 3-color FCI high sensitivity assay was used. The FCI results, qualified as "malignant" (FCI+) or "non-malignant" (FCI-), were compared to integrated definitive diagnosis established by clinicians based on all available information. MPE was finally diagnosed in 182 samples and FCI detected 141/182 (77.5%). Morphology further confirmed FCI findings by cytopathology detection of malignant cells in PE (n = 91) or histopathology (n = 29). Imaging tests and clinical history supported the diagnosis in the remaining samples. The median percentage of malignant cells was 6.5% for lymphoma and 0.23% for MPE secondary to epithelial cell malignancies. FCI identified a significantly lower percentage of EpCAM+ cells in cytopathology-negative MPE than in cytopathology-positive cases (0.02% vs. 1%; p < 0.0001). Interestingly, 29/52 MPE (55.8%) where FCI alerted of the presence of malignant cells were new diagnosis of cancer. Overall, FCI correctly diagnosed 456/522 samples (87.4%) suitable for comparison with cytopathology. These findings show that high sensitivity FCI significantly increases the diagnostic yield of MPE. Early detection of FCI + cases accelerates the diagnostic pathway of unsuspected MPE, thus supporting its implementation in clinical diagnostic work-up as a diagnostic tool.

Significance of p53 immunostaining in mesothelial proliferations and correlation with TP53 mutation status

p53 immunohistochemistry has long been proposed for the separation of benign from malignant mesothelial proliferations, with the older literature suggesting that any degree of positivity supported a diagnosis of mesothelioma. However, using modern immunohistochemistry platforms in other organ systems, notably gynecologic tumors, it has become clear that p53 staining can represent wild-type protein, and only specific staining patterns (absent, overexpression, or cytoplasmic expression) are indicative of a TP53 mutation. We applied these principles to two tissue microarrays containing 94 mesotheliomas and 66 reactive mesothelial proliferations. Seven/65 (11%) epithelioid mesotheliomas showed aberrant staining (four absent and three overexpression patterns) as did 5/29 (17%) of sarcomatoid mesotheliomas (all overexpression patterns). We sequenced the TP53 gene (exons 2-11) in five of the epithelioid and three of the sarcomatoid cases with aberrant staining as well as 12 epithelioid and eight sarcomatoid mesotheliomas with wild-type staining. All three sarcomatoid cases with aberrant staining showed mutated TP53, as did three of the epithelioid cases; in two of the epithelioid cases no mutation was detected, most likely because of large deletions not detected by this assay. In contrast, none of the 20 mesotheliomas with wild-type staining contained mutated TP53. We conclude that absent or overexpression p53 staining patterns can be used as a marker of a malignant vs. a benign mesothelial proliferation. The sensitivity of p53 staining by itself is low, but here addition of p53 to BAP1/MTAP staining increased sensitivity from 72 to 81% for epithelioid and 38 to 50% for sarcomatoid mesotheliomas.

UHRF1 Immunohistochemical Staining Separates Benign Reactive Spindle Cell Mesothelial Proliferations From Sarcomatoid Mesotheliomas

The separation of benign from malignant mesothelial proliferations is often a difficult pathologic problem. UHRF1 (ubiquitin-like with plant homeodomain and ring finger domains-1) is a regulator of DNA methylation and an epigenetic driver of various human cancers. It has recently been reported that UHRF1 is overexpressed in mesotheliomas. We asked whether UHRF1 immunohistochemistry could be used to separate benign from malignant mesothelial proliferations. Initial studies showed that UHRF1 stained mesothelial cells but also endothelial and other non-neoplastic cells, so that accurate counting of positive mesothelial cells was difficult. Therefore, we ran dual UHRF1-AE1/AE3 stains on 2 tissue microarrays containing 40 reactive mesothelial proliferations and 61 mesotheliomas and only counted UHRF1 staining in keratin-positive cells. On average 10.3±8.6% (mean±SD; range: 0% to 36, median: 6.8%) of epithelioid mesothelioma cells stained compared with 5.3±4.8% (range: 0% to 15%, median: 4.1%) of reactive epithelial mesothelial cells. This difference was statistically significant but there was too much overlap to use diagnostically. In contrast, 37±26% (range: 2.5% to 95%, median: 31%) of cells in sarcomatoid mesotheliomas compared with 1.2±1.2% (range: 0% to 3.0%, median: 1.0%) of cells in reactive spindle cell mesothelial proliferations stained. To confirm this difference we stained whole sections of 21 sarcomatoid mesotheliomas and 19 cases of organizing pleuritis. Staining of mesothelial cells was seen in 2.1±2.4% (range: 0% to 6.8%, median: 1.0%) of organizing pleuritis cases and 44±22% (range: 14% to 90%, median: 41%) of sarcomatoid mesotheliomas. We conclude that dual UHRF1-AE1/AE3 immunohistochemistry is very useful for separating benign spindle cell mesothelial proliferations from sarcomatoid mesotheliomas.