Pathology of mesothelioma

Mesothelioma

Mesothelioma arises from the surface serosal cells lining the pleural, peritoneal, and pericardial cavities. It has three variants including: epithelioid, sarcomatous/desmoplastic, and biphasic types. Mesothelioma cells, predominantly of the epithelioid type, can shed into effusions as sheets, clusters/ morulae, papillae, or single cells. The challenges to cytologic diagnosis of mesothelioma are two-fold: 1. distinguishing mesothelial cells from metastatic malignant (most commonly carcinoma) cells; 2. distinguishing reactive mesothelial from mesothelioma cells. Immunocytochemistry is a helpful aid to cytologic evaluation for the former. The distinction of reactive mesothelial cells from mesothelioma can be more difficult, as there is considerable overlap in their appearances in effusion specimens. Recently developed ancillary molecular and genetic tests are proving to be useful in confirming the diagnosis of malignant mesothelioma in cytology specimens.

Introduction to the second edition of 'Diagnostic Cytopathology of Serous Fluids' as CytoJournal Monograph (CMAS) in Open Access

Serous fluids are excessive accumulation of fluids in a serous cavity as effusion. However, traditionally this area also covers cytopathologic evaluation of washings of these cavities including pelvic/peritoneal washing. This is the introductory review article in series on this topic with the application of simplified algorithmic approaches. The series would be compiled finally as a book after minor modifications of individual review articles to accommodate the book layout on the topic as second edition of 'Diagnostic Cytopathology of Serous Fluids' book. The approach is primarily directed towards detection of neoplastic cells based on morphology alone or with the help of various ancillary tests, including commonly applied immunocytochemistry to be interpreted as second foreign population with application of SCIP (subtractive coordinate immunoreactivity pattern) approach in effusion fluid tapings. As the role of molecular pathology tests is increasing, this component as ancillary testing will also be covered as applicable. Because a picture and sketches are worth a thousand words, illustrations and figures are included generously even at the risk of moderate repetition. The clinically important serous cavities include peritoneal cavity, pericardial cavity, and two pleural cavities. The primary topic of this series is specimens from these cavities as effusion fluids and washings including cytopathologic evaluation of peritoneal/pelvic washing. It is expected that some readers may not read the entire series or the final book from beginning to end, but refer to the individual review articles and chapters sporadically during their clinical practice. Considering this practical limitation, some brief repetition may be observed throughout the book. Some of the important themes will be highlighted as italicized and bolded text for quick reference. Dedicated articles/chapters are assigned for technical and other reference material as appendices. Tables, algorithms, sketches, and combination of pictures are included generously for quick reference. Most of the illustrations are attempted to be labeled appropriately with arrows and other indicators to avoid equivocation, especially for beginners in the field. This introductory review article describes general details under the following three broad headings: Histology and general cytology of serous cavity lining Effusion (general considerations) Ancillary techniques in brief.

Malignant mesothelioma as a difficult interdisciplinary problem

The authors of the present report review the etiology and clinical symptoms of malignant pleural mesothelioma (MPM) as well as diagnostic techniques (both radiological and biomarkers) used for its detection. Subsequently, they present methods of multimodal treatment (surgery, chemotherapy, and radiotherapy) recommended by the International Mesothelioma Interest Group (IMIG). Finally, they discuss complications and long-term results associated with these methods of MPM treatment.

Pleomorphic epithelioid diffuse malignant pleural mesothelioma: a clinicopathological review and conceptual proposal to reclassify as biphasic or sarcomatoid mesothelioma

INTRODUCTION

In patients with epithelioid diffuse malignant pleural mesothelioma (DMPM), clinical stage is the current primary prognostic factor. We sought to investigate whether histologic subtyping can prognostically stratify patients with epithelioid DMPM.

METHODS

Hematoxylin and eosin-stained slides of 232 patients with epithelioid DMPM (14 stage I, 54 stage II, 130 stage III, and 34 stage IV) from a single institution were reviewed. We classified the tumors into five subtypes, according to the predominant histological pattern: trabecular, tubulopapillary, micropapillary, solid, and pleomorphic (≥10% of tumor).

RESULTS

Median overall survival (OS) of all patients with epithelioid DMPM was 16.2 months. Patients with pleomorphic subtype (n = 34) had the worst median OS (8.1 months), followed by solid (n = 89, 13.7 months), micropapillary (n = 20, 15.8 months), tubulopapillary (n = 51, 17.9 months), and trabecular (n = 38, 24.9 months). The pleomorphic subtype was associated with lymphatic and vascular invasion (p < 0.001). The micropapillary subtype was associated with lymphatic invasion (p < 0.001). In univariate analyses, pleomorphic subtype was significantly associated with poor OS (p = 0.003). The pleomorphic subtype showed no significant difference on OS compared with biphasic and sarcomatoid DMPM. In a multivariate analysis, the pleomorphic subtype was an independent predictor of poor OS (p = 0.031). In patients who underwent R1 resection, pleomorphic subtype had the shortest median time to recurrence (13.7 months).

CONCLUSION

Our finding that the pleomorphic subtype is a predictor of aggressive behavior in epithelioid DMPM with no survival difference from biphasic or sarcomatoid DMPM suggests that it may be best regarded as a sarcomatoid pattern rather than a subtype of epithelioid DMPM.

Occupational toxicology of asbestos-related malignancies

INTRODUCTION

Asbestos is banned in most Western countries but related malignancies are still of clinical concern because of their long latencies. This review identifies and addresses some controversial occupational and clinical aspects of asbestos-related malignancies.

METHODS

Papers published in English from 1980 to 2009 were retrieved from PubMed. A total of 307 original articles were identified and 159 were included.

ASSESSMENT OF EXPOSURE

The retrospective assessment of exposure is usually performed by using questionnaires and job exposure matrices and by careful collection of medical history. In this way crucial information about manufacturing processes and specific jobs can be obtained. In addition, fibers and asbestos bodies are counted in lung tissue, broncho-alveolar lavage, and sputum, but different techniques and interlaboratory variability hamper the interpretation of reported measurements. SCREENING FOR MALIGNANCIES: The effectiveness of low-dose chest CT screening in exposed workers is debatable. Several biomarkers have also been considered to screen individuals at risk for lung cancer and mesothelioma but reliable signatures are still missing. ATTRIBUTION OF LUNG CANCER: Exposures correlating with lung cancer are high and in the same range where asbestosis occurs. However, the unresolved question is whether the presence of fibrosis is a requirement for the attribution of lung cancer to asbestos. The etiology of lung cancer is difficult to define in cases of low-level asbestos exposure and concurrent smoking habits. MESOTHELIOMA: The diagnosis of malignant mesothelioma may also be difficult, because of procedures in sampling, fixation, and processing, and uses of immunohistochemical probes.

CONCLUSIONS

Assessment of exposure is crucial and requires accurate medical and occupational histories. Quantitative analysis of asbestos body burden is better performed in digested lung tissues by counting asbestos bodies by light microscopy and/or uncoated fibers by transmission electron microscopy. The benefits of screenings for asbestos-related malignancies are equivocal. The attribution of lung cancer to asbestos exposure is difficult in a clinical setting because of the need to assess asbestos body burden and the fact that virtually all these patients are also tobacco smokers or former smokers. Given the premise that asbestosis is necessary to causally link lung cancer to asbestos, it follows that the assessment of both lung fibrosis and asbestos body burden is necessary.

Characteristics of malignant pleural mesothelioma in women

BACKGROUND

The incidence of malignant pleural mesothelioma (MPM) is higher in men than in women, likely due to increased occupational asbestos exposure among men. Women also appear to experience better long-term survival. This study evaluates the role of gender in relation to established prognostic factors in MPM.

METHODS

We reviewed 715 cases of MPM treated with extrapleural pneumonectomy at our institution between July 1987 and December 2008. Data for patients with epithelial and nonepithelial tumors were analyzed separately. Kaplan-Meier and Cox regression analyses were used to estimate survival for various cohorts to assess the relationship between gender and survival independent of age at surgery, stage, side, and preoperative laboratory studies.

RESULTS

Of the 702 patients with complete data available, 114 out of 450 patients with epithelial tumors and 31 out of 252 patients with nonepithelial histology were women. Women with epithelial (and not nonepithelial) disease were found to differ significantly from men with respect to younger age, higher rate of thrombocytosis, and longer survival after surgery. The effect of gender on survival of patients with epithelial disease persisted when controlling for age, stage, thrombocytosis, leukocytosis, and anemia with a multivariable analysis. No significant differences in survival were seen among patients with nonepithelial disease with regard to gender, age, or anemia.

CONCLUSIONS

In the absence of other negative prognostic factors, women with epithelial MPM demonstrated a survival advantage. These findings support an aggressive approach to treating MPM including extrapleural pneumonectomy in individuals with favorable prognostic predictors, particularly women with epithelial histology and no other risk factors.

Identification of MCAM/CD146 as the target antigen of a human monoclonal antibody that recognizes both epithelioid and sarcomatoid types of mesothelioma

The prognosis for patients diagnosed with mesothelioma is generally poor, and currently available treatments are usually ineffective. Therapies that specifically target tumor cells hold much promise for the treatment of cancers that are resistant to current approaches. We have previously selected phage antibody display libraries on mesothelioma cell lines to identify a panel of internalizing human single chain (scFv) antibodies that target mesothelioma-associated, clinically represented cell surface antigens and further exploited the internalizing function of these scFvs to specifically deliver lethal doses of liposome-encapsulated small molecule drugs to both epithelioid and sarcomatous subtypes of mesothelioma cells. Here, we report the identification of MCAM/MUC18/CD146 as the surface antigen bound by one of the mesothelioma-targeting scFvs using a novel cloning strategy based on yeast surface human proteome display. Immunohistochemical analysis of mesothelioma tissue microarrays confirmed that MCAM is widely expressed by both epithelioid and sarcomatous types of mesothelioma tumor cells in situ but not by normal mesothelial cells. In addition, quantum dot-labeled anti-MCAM scFv targets primary meosthelioma cells in tumor fragment spheroids cultured ex vivo. As the first step in evaluating the therapeutic potential of MCAM-targeting antibodies, we performed single-photon emission computed tomography studies using the anti-MCAM scFv and found that it recognizes mesothelioma organotypic xenografts in vivo. The combination of phage antibody library selection on tumor cells and rapid target antigen identification by screening the yeast surface-displayed human proteome could be a powerful method for mapping the targetable tumor cell surface epitope space.

Problems in mesothelioma diagnosis

Many centres are now seeing increasing numbers of patients with malignant mesothelioma. This presents pathologists involved in making the diagnosis with a number of problems, which can be divided into those encountered in making the distinction between mesothelioma and benign changes and those experienced in separating mesotheliomas from other types of epithelial and connective tissue tumours. Immunohistochemistry plays a major role in helping to make the diagnosis, but it should be interpreted with due regard to the clinical setting and radiological features, and with a knowledge of the wide morphological variations seen in mesothelioma. This review identifies some of these problems and addresses the uses and limitations of immunohistochemistry in different situations. It includes a discussion of some of the less common variants of mesothelioma and other pleural-based tumours that enter into the differential diagnosis.

Application of immunohistochemistry to the diagnosis of malignant mesothelioma

CONTEXT

The diagnosis of malignant mesothelioma (MM) is rendered with the aid of immunohistochemistry to demonstrate the presence of "mesothelial," "epithelial," or "sarcomatous" differentiation. Antibody panels that have been proposed for the distinction between MM and other neoplasms usually include 2 or more epithelial markers used to exclude the diagnosis of a carcinoma, such as monoclonal and polyclonal carcinoembryonic antigen, Ber-EP4, B72.3, CD15, MOC-31, thyroid transcription factor 1, BG8, and others, and 2 or more mesothelial markers used to confirm the diagnosis of MM, such as cytokeratin 5/6, calretinin, HBME-1, thrombomodulin, WT-1, mesothelin, D2-40, and podoplanin. In general, most antibody panels provide excellent sensitivity and specificity for the differential diagnosis between MM epithelial variant and adenocarcinoma, particularly of lung origin. However, the accuracy of these markers is lower for the diagnosis of sarcomatous MM and for the differential diagnosis between MM and squamous cell carcinoma and carcinomas of renal, ovarian, and other origin.

OBJECTIVE

To identify optimal antibody panels for the diagnosis of MM.

DATA SOURCES

Literature review to determine how many and which mesothelial and epithelial markers need to be included in differential diagnosis antibody panels.

CONCLUSIONS

Various antibody panels have been recommended for the diagnosis of MM, with no overall consensus about how many and which markers should be used. A recent study with Bayesian statistics has demonstrated that the use of many markers does not provide higher diagnostic accuracy than the use of selected single antibodies or various combinations of only 2 markers. There is a need for the development of evidence-based or consensus-based guidelines for the diagnosis of MM in different differential diagnosis situations.

Pathology of the Pleura

The pleura and lung are intimately associated and share many pathologic conditions. Nevertheless, they represent two separate organs of different embryonic derivation and with different yet often symbiotic functions. In this article, the authors explore the pathologic manifestations of the many conditions that primarily or secondarily affect the pleura.

Management of Malignant Pleural Mesothelioma

Malignant mesothelioma is increasing in incidence globally and has no known cure. Its unique clinical feature of local infiltration along tissue planes makes it a difficult neoplasm to manage. There have been few randomized controlled trials regarding treatment options, although these have increased in recent years, and results are eagerly awaited. This article summarizes important advances in the management of mesothelioma, especially diagnostic and therapeutic aspects.

Recognition of Histopathologic Patterns of Diffuse Malignant Mesothelioma in Differential Diagnosis of Pleural Biopsies

Context.—Diffuse malignant mesothelioma is generally divided into 3 basic histologic types—epithelial, biphasic, or sarcomatous. However, a great diversity of histologic patterns exists within these 3 basic histologic types.

Design.—The diverse histologic patterns of diffuse malignant mesothelioma are briefly described, including infrequently encountered patterns.

Results. The histologic patterns of diffuse malignant mesothelioma provide a wide variation of features for the pathologist to consider in the differential diagnosis of a pleural biopsy.

Conclusion.—Pathologists should be aware of the varied histologic patterns of diffuse malignant mesothelioma when evaluating pleural biopsies.