The diagnostic utility of p16 FISH and GLUT-1 immunohistochemical analysis in mesothelial proliferations

Young investigator challenge: MicroRNA-21/MicroRNA-126 profiling as a novel tool for the diagnosis of malignant mesothelioma in pleural effusion cytology

BACKGROUND

In pleural effusion cytology, the distinction of malignant mesothelioma (MM) from reactive mesothelial cells (RMCs) may be challenging, even with the aid of immunocytochemistry or fluorescence in situ hybridization. It has been demonstrated that several microRNAs (miRNAs) are useful for this purpose in cell lines and histologic samples. In the current study, the authors evaluated the utility of an miRNA-based classifier as a complement to cytology.

METHODS

Quantitative reverse transcriptase-polymerase chain reaction analysis of 15 miRNAs was performed in mesothelial (MET-5A) and MM (H28 and H2052) cell lines. Significant miRNAs were validated in 51 MM and 40 nonneoplastic pleural histologic samples and then were tested in 29 MM and 24 RMC cytologic specimens. The performance of individual and combined miRNAs was assessed for their ability to differentiate between MM and RMCs.

RESULTS

MiRNA-19a (MiR-19a), miR-19b, miR-21, miR-25, and miR-126 were differentially expressed in cell lines and histologic samples. MiR-126 was down-regulated in MM surgical specimens compared with nonneoplastic specimens, whereas all of the other miRNAs were overexpressed. In cytologic specimens, all miRNAs except miR-25 were confirmed, exhibiting a sensitivity or a specificity higher than the threshold of 0.80, as recommended by the International Mesothelioma Interest Group. The best classifier resulted from the combination of miR-21 and miR-126, which achieved 0.86 sensitivity and 0.87 specificity.

CONCLUSIONS

Subject to validation of the current results in further larger studies, miR-21 and miR-126 profiling could be an effective and reliable tool for the diagnosis of MM in pleural effusions complementary to cytology evaluation.

Deletion status of p16 in effusion smear preparation correlates with that of underlying malignant pleural mesothelioma tissue

Differentiating malignant pleural mesothelioma (MPM) cells morphologically from reactive mesothelial hyperplasia cells is problematic. Homozygous deletion (HD) of p16 (CDKN2A), detected by FISH, is a good marker of malignancy and is useful to differentiate between these cells. However, the correlation between the p16 status of effusion smears and that of the underlying MPM tissues has not been investigated. We used p16‐specific FISH to investigate 20 cases of MPM from which both effusion cytologic smears and histologic specimens were available. In five cases, histologic specimens included both an invasive component and surface mesothelial proliferation. In 14 cases (70%), MPM cells in both tissue sections and effusion smears were p16 HD‐positive. Conversely, MPM cells in the remaining six tumors (30%) were p16 HD‐negative in both tissue sections and effusion smears. For all five MPM cases with surface mesothelial proliferations and invasive components, the effusion smears, surface mesothelial proliferations, and invasive MPM components all displayed p16 deletion. Moreover, the extent to which p16 was deleted in smears highly correlated with the extent of p16 deletion in tissues. The p16 deletion percentages were also similar among smears, tissue surface proliferations, and invasive components. In cases with clinical and radiologic evidence of a diffuse pleural tumor, detection of p16 deletion in cytologic smear samples may permit MPM diagnosis without additional tissue examination. However, the absence of p16 deletion in cytologic smear samples does not preclude MPM.

Loss of expression of BAP1 is a useful adjunct, which strongly supports the diagnosis of mesothelioma in effusion cytology

Although most mesotheliomas present with pleural effusions, it is controversial whether mesothelioma can be diagnosed with confidence in effusion cytology. Therefore, an ancillary marker of malignant mesothelial cells applicable in effusions would be clinically valuable. BRCA-1-associated protein (BAP1) is a tumor suppressor gene, which shows biallelic inactivation in approximately half of all mesotheliomas. We investigated whether loss of BAP1 expression by immunohistochemistry can be used to support a diagnosis of mesothelioma in effusion cytology. Immunohistochemistry for BAP1 was performed on cell blocks and interpreted blinded. 43 of 75 (57%) effusions associated with confirmed mesothelioma showed negative staining with positive internal controls. Of 57 effusions considered to have atypical mesothelial cells in the absence of a definitive diagnosis of mesothelioma, 8 cases demonstrated negative staining for BAP1. On follow-up six of these patients received a definitive diagnosis of mesothelioma in the subsequent 14 months (two were lost to follow-up immediately, and mesothelioma could not be excluded). Only 5 of 100 consecutive benign effusions were interpreted as BAP1 negative. One of these patients died soon after and mesothelioma could not be excluded. On unblinded review the four other patients with apparently negative BAP1 staining but no malignancy lacked convincing positive staining in non-neoplastic cells suggesting that BAP1 immunohistochemistry may have initially been misinterpreted. 47 effusions with adenocarcinoma were BAP1 positive. We conclude that loss of BAP1 expression, while not definitive, can be used to support the diagnosis of mesothelioma in effusion cytology. We caution that interpretation of BAP1 immunohistochemistry on cell block may be difficult and that convincing positive staining in non-neoplastic cells is required before atypical cells are considered negative. We also note that BAP1 loss is not a sensitive test as it occurs in only half of all mesotheliomas and cannot be used to exclude the diagnosis.

BAP1 (BRCA1-associated protein 1) is a highly specific marker for differentiating mesothelioma from reactive mesothelial proliferations

The distinction between malignant mesothelioma and reactive mesothelial proliferation can be challenging both on histology and cytology. Recently, variants of the BRCA1-associated protein 1 (BAP1) gene resulting in nuclear protein loss were reported in hereditary and sporadic mesothelioma. Using immunohistochemistry, we evaluated the utility of BAP1 expression in the differential diagnosis between mesothelioma and other mesothelial proliferations on a large series of biopsies that included 212 mesotheliomas, 12 benign mesothelial tumors, and 42 reactive mesothelial proliferations. BAP1 stain was also performed in 70 cytological samples (45 mesotheliomas and 25 reactive mesothelial proliferations). BAP1 was expressed in all benign mesothelial tumors, whereas 139/212 (66%) mesotheliomas were BAP1 negative, especially in epithelioid/biphasic compared with sarcomatoid/desmoplastic subtypes (69% vs 15%). BAP1 loss was homogeneous in neoplastic cells except for two epithelioid mesotheliomas showing tumor heterogeneity. By fluorescence in situ hybridization, BAP1 protein loss was paralleled by homozygous deletion of the BAP1 locus in the vast majority of BAP1-negative tumors (31/41, 76%), whereas 9/10 BAP1-positive mesotheliomas were normal. In biopsies interpreted as reactive mesothelial proliferation BAP1 loss was 100% predictive of malignancy, as all 6 cases subsequently developed BAP1-negative mesothelioma, whereas only 3/36 (8%) BAP1-positive cases progressed to mesothelioma. On cytology/cell blocks, benign mesothelial cells were invariably positive for BAP1, whereas 64% of mesotheliomas showed loss of protein; all 6 cases showing BAP1 negativity were associated with histological diagnosis of BAP1-negative mesothelioma. BAP1 stain also showed utility in the differential of mesothelioma from most common pleural and peritoneal mimickers, such as lung and ovary carcinomas, with specificity and sensitivity of 99/70% and 100/70%, respectively. Our results show that BAP1 protein is frequently lost in mesothelioma, especially of epithelioid/biphasic subtype and is commonly associated with homozygous BAP1 deletion. BAP1 immunostain represents an excellent biomarker with an unprecedented specificity (100%) in the distinction between benign and malignant mesothelial proliferations. Finding BAP1 loss in mesothelial cells should prompt to immediately reevaluate the patient; moreover, it might be useful in mapping tumor extent and planning surgical resection.

MDM2 is an important prognostic and predictive factor for platin-pemetrexed therapy in malignant pleural mesotheliomas and deregulation of P14/ARF (encoded by CDKN2A) seems to contribute to an MDM2-driven inactivation of P53

Background:

Malignant pleural mesothelioma (MPM) is a highly aggressive tumour that is first-line treated with a combination of cisplatin and pemetrexed. Until now, predictive and prognostic biomarkers are lacking, making it a non-tailored therapy regimen with unknown outcome. P53 is frequently inactivated in MPM, but mutations are extremely rare. MDM2 and P14/ARF are upstream regulators of P53 that may contribute to P53 inactivation.

Methods:

A total of 72 MPM patients were investigated. MDM2 immunoexpression was assessed in 65 patients. MDM2 and P14/ARF mRNA expression was analysed in 48 patients of the overall collective. The expression results were correlated to overall survival (OS) and progression-free survival (PFS).

Results:

OS and PFS correlated highly significantly with MDM2 mRNA and protein expression, showing a dismal prognosis for patients with elevated MDM2 expression (for OS: Score (logrank) test: P⩽0.002, and for PFS: Score (logrank) test; P<0.007). MDM2 was identified as robust prognostic and predictive biomarker for MPM on the mRNA and protein level. P14/ARF mRNA expression reached no statistical significance, but Kaplan–Meier curves distinguished patients with low P14/ARF expression and hence shorter survival from patients with higher expression and prolonged survival.

Conclusions:

MDM2 is a prognostic and predictive marker for a platin–pemetrexed therapy of patients with MPMs. Downregulation of P14/ARF expression seems to contribute to MDM2-overexpression-mediated P53 inactivation in MPM patients.

Utility of Immunohistochemistry in the Diagnosis of Pleuropulmonary and Mediastinal Cancers: A Review and Update

Context

Immunohistochemistry has become an indispensable ancillary tool for the accurate classification of pleuropulmonary and mediastinal neoplasms necessary for therapeutic decisions and predicting prognostic outcome in the era of personalized medicine. Diagnostic accuracy has significantly improved because of the continuous discoveries of tumor-associated biomarkers and the development of effective immunohistochemical panels.

Objective

To increase the accuracy of diagnosis and classify pleuropulmonary neoplasms through immunohistochemistry.

Data Sources

Literature review, authors' research data, and personal practice experience.

Conclusions

This review article has shown that appropriately selecting immunohistochemical panels enables pathologists to effectively diagnose most primary pleuropulmonary neoplasms and differentiate primary lung tumors from a variety of metastatic tumors to the lung. The discovery of new mutation-specific antibodies identifying a subset of specific gene-arranged lung tumors provides a promising alternative and cost-effective approach to molecular testing. Knowing the utilities and pitfalls of each tumor-associated biomarker is essential to avoiding potential diagnostic errors.

Practical utility of insulin-like growth factor II mRNA-binding protein 3, glucose transporter 1, and epithelial membrane antigen for distinguishing malignant mesotheliomas from benign mesothelial proliferations

The differentiation of malignant mesotheliomas and benign mesothelial proliferations is crucial in determining patient care and prognosis. But, this distinction can be extremely difficult, particularly in small biopsies. Recently, insulin-like growth factor II mRNA-binding protein 3 (IMP3) and glucose transporter 1 (GLUT-1) have been reported as specific and sensitive markers in the distinction of mesotheliomas from benign mesothelial proliferations. The purpose of this study is to evaluate the utility of IMP3, GLUT-1, and epithelial membrane antigen (EMA) immunohistochemistry for distinguishing mesotheliomas from benign mesothelial proliferations. Immunoexpression of IMP3, GLUT-1, and EMA was evaluated in 88 malignant mesotheliomas, 35 adenomatoid tumors, and 20 benign lung tissues with reactive mesothelial cells. The sensitivity for IMP3, GLUT-1, and EMA was 37%, 21%, and 41%, respectively. The specificity for IMP3, GLUT-1, and EMA was 100%. When IMP3, GLUT1, and EMA combined, the sensitivity was 66% for IMP3/EMA staining, 53% for GLUT-1/EMA staining, and 45% for IMP3/GLUT-1. Use of IMP3 and EMA together is more helpful to distinguish malignant mesotheliomas from benign mesothelial proliferations than the use of IMP3 or EMA alone.

A rare cause of heart failure with preserved ejection fraction: primary pericardial mesothelioma masquerading as pericardial constriction

We present a case of a 30-year-old woman with a history of HIV and hepatitis C who sought medical attention because of severe oedema of the lower limbs and abdomen. CT of the chest showed a thickened pericardium, and cardiac catheterisation demonstrated constrictive physiology. She underwent pericardiectomy, but the procedure was unsuccessful because the pericardium was densely adherent to the myocardium. After consultation with several pathologists, she was diagnosed with primary pericardial mesothelioma (PPM), an exceedingly rare cardiac tumour with a fatal prognosis. She died within 3 months of presentation. The details of the case as well as pertinent literature are reviewed.

Metastatic Tumors of Unknown Origin: Ancillary Testing in Cytologic Specimens

The application of ancillary studies, such as immunostains, to cytopathology has improved the ability to make accurate diagnoses with precise subclassification. Even with these techniques, there are still aspiration and exfoliative cytology cases for which it remains difficult to definitively determine the source and/or subtype. This article focuses on the well-established and novel ancillary studies used in the modern era of cancer diagnoses in cytopathology, particularly in the diagnostic work-up of metastatic tumors without a known primary.

[Mesothelial proliferation in rectal cancer]

In an epiphrenic lymph node of a 55 years old female patient who underwent surgical resection of a rectal adenocarcinoma epitheloid proliferations with papillary and solid growth pattern were seen additional to a metastasis of the carcinoma. Adjacent vessels contained similar infiltrates. Immunohistochemically a co-expression of pan-keratin, calretinin and WT1 was seen, suggestive for a diagnosis of a metastasis of a malignant mesothelioma. However, radiologic examination yielded no morphologic correlate to this suspicion. Further immunohistochemical work-up showed positivity for desmin, negativity for EMA, GLUT1, p53 and a low ki67-fraction of 2-3 %. Therefore, a final diagnosis of benign mesothelial proliferations disseminated into the lymph node and the adjacent vessels was made.

Comparative immunohistochemical analysis of IMP3, GLUT1, EMA, CD146, and desmin for distinguishing malignant mesothelioma from reactive mesothelial cells

OBJECTIVES

To identify useful biomarkers for differentiating between malignant mesothelioma (MM) and reactive mesothelial cells (RMCs).

METHODS

Formalin-fixed, paraffin-embedded (FFPE) tissues from 34 MM and 40 RMC samples were analyzed using immunohistochemistry, and the findings were compared.

RESULTS

Positive markers for MM included insulin-like growth factor 2 messenger RNA binding protein 3 (IMP3), glucose transporter 1 (GLUT1), epithelial membrane antigen (EMA), and CD146, which showed sensitivities of 94%, 85%, 79%, and 71% and specificities of 78%, 100%, 88%, and 98%, respectively. In sarcomatoid MM, EMA had significantly lower expression than did IMP3, GLUT1, and CD146 (P < .001). The areas under receiver operating characteristic curves were the highest for IMP3 (0.95), followed by GLUT1 (0.93). When the optimal cutoff points for IMP3 (30%) and GLUT1 (10%) were used, the sensitivity of IMP3 and GLUT1 for MM was 100%, and the specificity of both for MM was 95%.

CONCLUSIONS

The combination of IMP3 and GLUT1 is most appropriate for distinguishing MM from RMC using FFPE sections.

Is galectin-3 antibody a useful marker in the diagnosis of malignant pleural mesothelioma?

Malignant pleural mesothelioma (MPM) is a challenging diagnosis characterized by the absence of real specific diagnostic markers. Positivity with the galectin-3 antibody was assessed by a cytoplasmic expression in 17 MPM. Fourteen cases expressed the galectin-3 antibody. The three negative cases consisted of epithelioid, biphasic, and sarcomatoid MPM. The 14 positive cases consisted of epithelioid MPM in 12 cases, sarcomatoid MPM in one case, and biphasic MPM in one case. In spite of our inability to prove the real diagnostic value of the galectin-3 antibody, our findings make us wonder about the implication of this antibody in the carcinogenesis of MPM.

Malignant peritoneal mesothelioma treated by cytoreductive surgery and hyperthermic intraperitoneal chemotherapy: is GLUT1 expression a major prognostic factor? A preliminary study

PURPOSE

Diffuse malignant peritoneal mesothelioma (DMPM) is a rare primary peritoneal malignancy. Its prognosis has been improved by an aggressive locoregional treatment combining extensive cytoreductive surgery (CRS) and hyperthermic intraperitoneal chemotherapy (HIPEC). Prognostic factors are currently poorly defined for this disease but are essential if treatment is to be standardized.

METHODS

Twenty-eight patients with DMPM, who were considered preoperatively to be candidates for CRS and HIPEC between June 1998 and August 2010 at our institution, were selected for this study. Medical records and histopathological features were retrospectively reviewed and 24 clinical, histological, and immunohistochemical parameters were assessed for their association with overall survival by univariate and multivariate analyses.

RESULTS

The following factors were significantly associated with overall survival by univariate analysis: predominant histological growth pattern in the epithelioid areas, nuclear grooves in the epithelioid areas, atypical mitoses, and calretinin and GLUT1 expression by immunohistochemistry in the epithelioid areas. Expression of the facilitative glucose transporter protein GLUT1 in the epithelioid areas was the only factor independently associated with overall survival by multivariate analysis.

CONCLUSIONS

GLUT1 expression appears to be an indicator of poor prognosis in DMPM. Standard histological classification of DMPM may not be adequate to select patients for aggressive locoregional treatments, such as CRS and HIPEC. Multicenter validation of the prognostic factors identified in this preliminary study is needed to refine patient selection for potential cure.

Diagnostic value of fluorescence in situ hybridization assay in malignant mesothelioma: a meta-analysis

The diagnosis of malignant mesothelioma (MM) remains a clinical challenge and the fluorescence in situ hybridization (FISH) assay has been reported to be one promising tool. The present meta-analysis aimed to establish the overall diagnostic accuracy of FISH for diagnosing MM. After a systematic review of English language studies, the sensitivity, specificity and other measures of accuracy of FISH in the diagnosis of MM were pooled using random-effects models. Summary receiver operating characteristic curves were applied to summarize overall test performance. Nine studies met our inclusion criteria, the pooled sensitivity and specificity for FISH for diagnosing MM being 0.72 (95% CI 0.67-0.76) and 1.00 (95% CI 0.98-1.00), respectively. The positive likelihood ratio was 34.5 (95% CI 14.5-82.10), the negative likelihood ratio was 0.24 (95% CI 0.16-0.36), and the diagnostic odds ratio was 204.9 (95% CI 76.8-546.6), the area under the curve being 0.99. Our data suggest that the FISH assay is likely to be a useful diagnostic tool for confirming MM. However, considering the limited studies and patients included, further large scale studies are needed to confirm these findings.

Abdominopelvic washings: A comprehensive review

Intraperitoneal spread may occur with gynecological epithelial neoplasms, as well as with non-gynecological malignancies, which may result in serosal involvement with or without concomitant effusion. Therefore, washings in patients with abdominopelvic tumors represent important specimens for cytologic examination. They are primarily utilized for staging ovarian cancers, although their role has decreased in staging of endometrial and cervical carcinoma. Abdominopelvic washings can be positive in a variety of pathologic conditions, including benign conditions, borderline neoplastic tumors, locally invasive tumors, or distant metastases. In a subset of cases, washings can be diagnostically challenging due to the presence of co-existing benign cells (e.g., mesothelial hyperplasia, endosalpingiosis, or endometriosis), lesions in which there is only minimal atypia (e.g., serous borderline tumors) or scant atypical cells, and the rarity of specific tumor types (e.g., mesothelioma). Ancillary studies including immunocytochemistry and fluorescence in situ hybridization may be required in difficult cases to resolve the diagnosis. This article provides a comprehensive and contemporary review of abdominopelvic washings in the evaluation of gynecologic and non-gynecologic tumors, including primary peritoneal and mesothelial entities.

Diagnostic usefulness of p16/CDKN2A FISH in distinguishing between sarcomatoid mesothelioma and fibrous pleuritis

The distinction between sarcomatoid mesothelioma and fibrous pleuritis is difficult based on histology, especially when the amount of tumor tissue examined via biopsy is small and immunohistochemical examination is inconclusive. We studied the usefulness of deletion of p16 with fluorescence in situ hybridization (FISH) and p16 hypermethylation with polymerase chain reaction for the diagnosis and prognosis of malignant pleural mesothelioma (MPM). We analyzed 50 MPMs, including 22 sarcomatoid mesothelioma cases and 10 fibrous pleuritis cases. We set the cutoff value of homozygous deletion pattern as 14.4% based on FISH signaling patterns using samples of fibrous pleuritis. The percentage of homozygous deletion pattern was higher than 14.4% in 55.6% of the epithelioid mesotheliomas (10/18) and in all of the sarcomatoid mesotheliomas (22/22). Methylation of p16 was observed in 7 (20.6%) of 34 informative cases. p16 FISH analysis can be a reliable test for distinguishing between sarcomatoid mesothelioma and fibrous pleuritis and a prognostic factor for MPM.

Guidelines for pathologic diagnosis of malignant mesothelioma: 2012 update of the consensus statement from the International Mesothelioma Interest Group

CONTEXT

Malignant mesothelioma (MM) is an uncommon tumor that can be difficult to diagnose.

OBJECTIVE

To provide updated practical guidelines for the pathologic diagnosis of MM.

DATA SOURCES

Pathologists involved in the International Mesothelioma Interest Group and others with an interest in the field contributed to this update. Reference material includes peer-reviewed publications and textbooks.

CONCLUSIONS

There was consensus opinion regarding (1) distinction of benign from malignant mesothelial proliferations (both epithelioid and spindle cell lesions), (2) cytologic diagnosis of MM, (3) key histologic features of pleural and peritoneal MM, (4) use of histochemical and immunohistochemical stains in the diagnosis and differential diagnosis of MM, (5) differentiation of epithelioid MM from various carcinomas (lung, breast, ovarian, and colonic adenocarcinomas, and squamous cell and renal cell carcinomas), (6) diagnosis of sarcomatoid mesothelioma, (7) use of molecular markers in the diagnosis of MM, (8) electron microscopy in the diagnosis of MM, and (9) some caveats and pitfalls in the diagnosis of MM. Immunohistochemical panels are integral to the diagnosis of MM, but the exact makeup of panels used is dependent on the differential diagnosis and on the antibodies available in a given laboratory. Immunohistochemical panels should contain both positive and negative markers. It is recommended that immunohistochemical markers have either sensitivity or specificity greater than 80% for the lesions in question. Interpretation of positivity generally should take into account the localization of the stain (eg, nuclear versus cytoplasmic) and the percentage of cells staining (>10% is suggested for cytoplasmic membranous markers). These guidelines are meant to be a practical reference for the pathologist.

Utility of Glucose Transporter 1 in the Distinction of Benign and Malignant Thoracic and Abdominal Mesothelial Lesions

Context.—Malignant mesothelioma, of either peritoneum or pleura, is an uncommon cancer. The diagnosis is often difficult to make, in part because of the overlapping morphology of reactive and malignant mesothelial cells. Glucose transporter 1 (GLUT-1) is a glucose transporter typically found on erythrocytes, which is aberrantly expressed in various carcinomas. It has recently been reported as specific and sensitive in discriminating malignant pleural mesothelioma from reactive hyperplasia. The application of GLUT-1 staining in peritoneal mesothelioma has not been fully explored.

Objective.—To determine if GLUT-1 staining is helpful in distinguishing abdominal mesotheliomas from benign, reactive mesothelial lesions and to further study its utility in the thorax.

Design.—Tissue microarrays containing 135 abdominal malignant mesotheliomas and 30 malignant pleural mesotheliomas were stained with an antibody to GLUT-1, as were 56 reactive mesothelial lesions.

Results.—The overall sensitivity and specificity for GLUT-1 in mesothelioma was 53% and 98%, respectively. The sensitivity in epithelioid malignant mesothelioma was 49% and in sarcomatoid/biphasic malignant mesothelioma, 66%. In the thorax, the sensitivity was 50% and in the abdomen it was 54%. The positive predictive value of GLUT-1 immunoreactivity was 98% and the negative predictive value was 40%.

Conclusion.—Glucose transporter 1 staining of thoracic mesotheliomas showed high specificity but lower sensitivity than previously reported. Abdominal malignant mesotheliomas showed similar results. Because of low sensitivity, only positive staining is informative. In both sites, the utility of the stain was limited by nonspecific staining (eg, in necrotic areas) as well as bright labeling of erythrocytes and occasional lymphoid elements. Despite these limitations, GLUT-1 can help differentiate malignant mesothelioma from reactive benign mesothelium.

Pathological and molecular biological approaches to early mesothelioma

Malignant mesothelioma is an asbestos-related malignancy that arises primarily from mesothelial cells on the serosal surfaces of the pleural, peritoneal, and pericardial cavities. Malignant pleural mesothelioma (MPM) is most common, and its incidence is dramatically increasing worldwide as a result of widespread use of asbestos. Morphological discrimination between MPM and reactive mesothelial hyperplasia is difficult, and the most reliable pathological criterion for malignancy is mesothelial proliferation invading deeply into subpleural adipose tissues. To establish radical cure of MPM, it is crucial to find early-stage MPM of epithelial type, in which mesothelial proliferation is localized on the serosal surface of parietal pleura or limited within the submesothelial fibrous tissues of parietal pleura. The initial clinical presentation for patients with MPM is frequently dyspnea and/or chest pain due to large pleural effusion, and cytological analysis of pleural effusions is valuable to find patients with early-stage MPM of epithelial type. Recently, cytological features of MPM in pleural effusion, molecular markers for MPM, and genetic alternations of MPM have been reported. In this review, we discuss major issues on pathological and molecular biological approaches for diagnosis of early-stage MPM of epithelial type.