Role of Histochemistry and Immunohistochemistry in the Diagnosis of Mesothelioma

Dr Sampurna Roy MD



Despite numerous histochemical, ultrastructural, and immuno-histochemical studies, differentiation between malignant epithelial pleural mesothelioma and adenocarcinoma of the lung remains extremely difficult.

Diagnosis of Mesothelioma is a problem for the following reasons:

1. Histopathological diversity in Mesothelioma

2. Pleural cavity is a common site for metastatic disease, florid reactive fibrosis and hyperplasia and less commonly primary sarcoma.

Accurate diagnosis of mesothelioma is necessary to assess the prognosis of the patient. It is also essential in relation to occupational-related compensation claims following exposure to asbestos.

Histochemical and immunohistochemical panel commonly used by pathologists:

PAS after diastase Negative, Rarely  Positive   Positive (adenocarcinoma)
Cytokeratin (AE1/AE3)  Positive   Positive
CK5/6  Positive   Negative
Thrombomodulin  Positive   Negative
Calretinin  Positive   Negative
CEA (monoclonal)  Negative   Positive
Leu M1  Negative   Positive
Ber EP4  Negative   Positive


Before the advent of immunohistochemistry , histochemical studies played an important role in the diagnosis of mesothelioma.

Mesothelioma produce the acid mucopolysaccharide, hyaluronic acid which can be identified by staining with Alcian blue (pH 2.5) with and without hyaluronidase.

Identification of neutral mucin droplets within tumour cells or tubular lumina by periodic acid - Schiff reaction with diastase pretreatment strongly indicates that the tumour is an adenocarcinoma and not mesothelioma.


 Immunodiagnosis of mesothelioma is one based on exclusion. There is no single immunohistochemical marker entirely specific for mesothelioma hence a panel of antibodies are used to establish the diagnosis.

Immunohistochemistry is useful in the following areas:

1. To differentiate between malignant epithelial mesothelioma and adenocarcinoma:

A combination of monoclonal antibodies to carcinoembryonic antigen (CEA) , Leu-M1 , Ber-EP4,  MOC31 or B72.3 can distinguish 90% pulmonary adenocarcinomas from pleural mesothelioma . In a recent publication, it was suggested that immunostaining for cytokeratin 5/6 could assist in distinguishing epithelial mesothelioma from lung adenocarcinoma.

Antimesothelioma antibodies are useful in identification of epithelial mesothelioma.  Thrombomodulin is extremely useful and is applicable to formalin fixed, paraffin embedded tissue.

2. To differentiate between malignant epithelial mesothelioma versus reactive mesothelial hyperplasia:

Epithelial membrane antigen (EMA)- strong and diffuse positive membrane staining and/or Human Milk Fat Globulin-2(HMG2) favours mesothelioma over hyperplasia.  EMA may rarely show patchy weak membrane staining of reactive mesothelium.  p53 protein is also highly specific for mesothelioma over reactive mesothelial hyperplasia (this is less specific than EMA). Staining for cytokeratin may be useful as it may help in the identification of invasion into deeper structures.

3. To differentiate between malignant sarcomatous mesothelioma  from sarcoma,  localized fibrous tumour and reactive serosal fibrosis :

The pancytokeratin marker AE1/AE3 and low molecular weight cytokeratin CAM5.2 are useful in the diagnosis of mesothelioma.

 Most sarcomas, reactive serosal fibrosis and localized fibrous tumours are cytokeratin negative. 

(Note:  Epithelioid variant of sarcoma ,  synovial sarcoma and leiomyosarcoma may occasionally show cytokeratin positivity ).

Vascular tumours:  Mesotheliomas do not express vascular markers (CD31, FactorVII ) .

Epithelioid leiomyosarcoma:  It may not be possible to differentiate epithelioid leiomyosarcoma from sarcomatoid variant of mesothelioma as smooth muscle differentiation may be present in the latter ( according to some authors these should be classified as leiomyoid mesothelioma ).

Synovial sarcoma:  These may be confused with mixed and sarcomatoid variants of mesothelioma. D-PAS mucin or positive immunostaining for adenocarcinoma markers in the epithelial elements are particularly useful. bcl2 protein is present in almost all cases of synovial sarcoma. It is rarely present in mesothelioma.

4. To differentiate malignant mesothelioma from lymphoma and thymoma:

Primary pleural lymphoma are high grade and are differentiated from mesothelioma by using cytokeratin and lymphoid markers.

Thymoma arising in pleura may be confused with solid and lymphohistiocytoid pattern of mesothelioma.  Immunohistochemistry is of little help in this area.



The diagnostic utility of immunohistochemistry in distinguishing between epithelioid mesotheliomas and squamous carcinomas of the lung: a comparative study. Mod Pathol. 2006;19(3):417-28.

Evaluation of 12 antibodies for distinguishing epithelioid mesothelioma from adenocarcinoma: identification of a three-antibody immunohistochemical panel with maximal sensitivity and specificity. Mod Pathol. 2006 Apr;19(4):514-23.

Immunohistochemical diagnosis of epithelioid mesothelioma: an update .  Arch Pathol Lab Med. 2005;129(11):1407-14.

Utility of D2-40, a novel mesothelial marker, in the diagnosis of malignant mesothelioma.Mod Pathol. 2005;18(1):105-10.

The diagnostic utility of immunohistochemistry in distinguishing between mesothelioma and renal cell carcinoma: a comparative study.Hum Pathol. 2004;35(6):697-710.

The immunohistochemical diagnosis of mesothelioma: a comparative study of epithelioid mesothelioma and lung adenocarcinoma.Am J Surg Pathol. 2003;27(8):1031-51.

Value of E-cadherin and N-cadherin immunostaining in the diagnosis of mesothelioma.Hum Pathol. 2003;34(8):749-55.

E-cadherin, E-selectin and vascular cell adhesion molecule: immunohistochemical markers for differentiation between mesothelioma and metastatic pulmonary adenocarcinoma?Virchows Arch. 2002 Jul;441(1):41-6. Epub 2001 Nov 16.

Calretinin, thrombomodulin, CEA, and CD15: a useful combination of immunohistochemical markers for differentiating pleural epithelial mesothelioma from peripheral pulmonary adenocarcinoma.Hum Pathol. 2001 May;32(5):529-36.

Pulmonary adenocarcinoma simulating malignant mesothelioma.Arch Pathol Lab Med. 2001 Dec;125(12):1598-600.

Value of thyroid transcription factor-1, E-cadherin, BG8, WT1, and CD44S immunostaining in distinguishing epithelial pleural mesothelioma from pulmonary and nonpulmonary adenocarcinoma.Am J Surg Pathol. 2000 ;24(4):598-606.

Value of Cytokeratin 5/6 Immunostaining in Distinguishing Epithelial Mesothelioma of the Pleura From Lung Adenocarcinoma.Am J Surg Pathol. 1998;22(10):1215-1221

Value of the Ber-EP4 antibody in differentiating epithelial pleural mesothelioma from adenocarcinoma. The M.D. Anderson experience and a critical review of the literature.Am J Clin Pathol. 1998 Jan;109(1):85-9.

Value of thrombomodulin immunostaining in the diagnosis of mesothelioma.Histopathology. 1997 Jul;31(1):25-30

A comparative immunohistochemical study of malignant mesothelioma and renal cell carcinoma: the diagnostic utility of Leu-M1, Ber EP4, Tamm-Horsfall protein and thrombomodulin.Histopathology. 1995 Oct;27(4):361-6.

Diagnostic tools for differentiating between pleural mesothelioma and lung adenocarcinoma in paraffin embedded tissue. Part I: Immunohistochemical findings.Virchows Arch A Pathol Anat Histopathol. 1993;423(1):19-27.

Malignant epithelioid pleural mesothelioma versus peripheral pulmonary adenocarcinoma: a histochemical, ultrastructural, and immunohistologic study of 103 cases.Hum Pathol. 1990;21(7):759-66.

The immunohistochemical diagnosis of mesothelioma. Differentiation of mesothelioma and lung adenocarcinoma.Am J Surg Pathol. 1989 Apr;13(4):276-91.

February 2010

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