Immunophenotyping of malignant mesothelioma

Extrathoracic Mesothelial Proliferations and Their Mimics

Mesothelial proliferations, either reactive or neoplastic in nature, often pose difficult diagnostic dilemmas. Electron microscopy continues to be a gold standard in the identification of mesothelial differentiation. However, it is very common to apply long panels of antibodies for that purpose. In most cases, light microscopy and immunohistochemistry will solve the problem. However, the definitive, specific, and sensitive immunohistochemical marker is still lacking. This is particularly true in peritoneal and testicular mesothelial tumors, in which common embryologic origin with epithelial elements results in overlapping immunohistochemistry and morphology. The particularities of peritoneal and testicular mesothelial proliferations, and the main tumors that may mimic them in these sites, as well as the value and limitations of immunohistochemistry and electron microscopy in their differential diagnosis are the subject of this review.

Sensitivity and specificity of immunohistochemical markers used in the diagnosis of epithelioid mesothelioma: a detailed systematic analysis using published data

AIMS

Immunohistochemistry is frequently employed to aid the distinction between mesothelioma and pulmonary adenocarcinoma metastatic to the pleura, but there is uncertainty as to which antibodies are most useful. We analysed published data in order to establish sensitivity and specificity of antibodies used to distinguish between these tumours with a view to defining the most appropriate immunohistochemical panel to use when faced with this diagnostic problem.

METHODS AND RESULTS

A systematic analysis of the results of 88 published papers comparing immunohistochemical staining of a panel of antibodies in mesothelioma with epithelioid areas, and pulmonary adenocarcinoma metastatic to the pleura. Results for a total of 15 antibodies were analysed and expressed in terms of sensitivity and specificity. The most sensitive antibodies for identifying pulmonary adenocarcinoma were MOC-31 and BG8 (both 93%), whilst the most specific were monoclonal CEA (97%) and TTF-1 (100%). The most sensitive antibodies to identify epithelioid mesothelioma were CK5/6 (83%) and HBME-1 (85%). The most specific antibodies were CK5/6 (85%) and WT1 (96%).

CONCLUSIONS

No single antibody is able to differentiate reliably between these two tumours. The use of a small panel of antibodies with a high combined sensitivity and specificity is recommended.

Immunophenotypings of malignant epithelial mesothelioma and their roles in the differential diagnosis

To investigate the immunophenotypings of malignant epithelial mesothelioma (MEM), and to seek the valuable markers in distinguishing peritoneal MEM from peritoneal metastatic ovarian adenocarcinoma (OA) and colorectal adenocarcinoma (CA), immunohistochemical SP method was used to detect expressions of HBME-1, E-cadherin, CA19-9, MOC-31 and CK7 in paraffin-embedded tissues of 18 cases of MEM, 20 OA and 20 CA. The results showed that there was a significant difference in the expressions of E-cadherin, CA19-9 and MOC-31 between MEM and OA group (P<0.05). Similarly, the difference in the expression of HBME-1, E-cadherin, CA19-9, MOC-31 and CK7 between MEM and CA groups is significant (P<0.05). These results indicate that HBME-1 could be used as a positive marker in distinguishing MEM from CA. E-cadherin, CA19-9 and MOC-31 are considered to be useful negative markers in diagnostic distinction between MEM and metastatic adenocarcinomas, including OA and CA. CK7 is the best positive marker in distinguishing MEM from CA, but this marker appears to be valueless in discriminating MEM from OA.

HBME-1 immunostaining in thyroid tumors especially in follicular neoplasm

It is generally known that even with permanent sections, the differential diagnosis between follicular adenoma and follicular carcinoma is often difficult to determine. It is not unusual to encounter patients diagnosed with benign follicular adenoma whose diagnoses have to be changed to malignancies because of recurrence or metastasis. As the monoclonal antibody HBME-1 produced by mesothelioma cells has been shown to have reactivity in thyroid carcinomas, we investigated the diagnostic usefulness of HBME-1 in follicular neoplasms. Immunohistochemical staining for HBME-1 was performed on 205 various thyroid tumors using the labeled streptavadin biotin peroxidase method. When hematoxylin-eosin (HE) staining was performed again for this study and all cases were examined in accordance with the WHO Histological Classifications 2nd Edition, 87.2% (54/62) of adenomatous goiter and 72.6% (45/62) of follicular adenoma were negative. On the other hand, 84.6% (33/39) of follicular carcinoma and 97.2% (35/36) of papillary carcinoma were positive. All anaplastic (2/2) and medullary (4/4) carcinoma were negative. Examination in follicular neoplasms had a sensitivity of 84.6%, specificity of 72.6%, positive predictive value of 66.0% and overall accuracy of 77.2%. Among the cases treated as follicular adenoma clinically, the diagnosis of 13 cases was changed to follicular carcinoma, and 6 cases to papillary carcinoma for this study. These cases showed strong HBME-1 positivity. Two of the follicular carcinoma cases experienced recurrence. We conclude that immunohistochemical staining with HBME-1 may be useful clinically to pick out cases with a high risk of recurrence in follicular carcinoma, and that benign adenoma cases need close follow-up.

Combined use of novel epithelial (MOC-31) and mesothelial (HBME-1) immunohistochemical markers for optimal first line diagnostic distinction between mesothelioma and metastatic carcinoma in pleura

AIMS

To determine the value of immunohistochemistry in differentiation of malignant pleural mesothelioma from carcinoma in a pleural biopsy we optimized a double panel of MOC-31 and HBME-1 and compared the results with others from the literature.

METHODS AND RESULTS

A multi-antibody panel was applied to biopsy samples from 44 cases of malignant pleural mesothelioma and 23 cases of carcinoma metastatic to the pleura. We used monoclonal antibodies against keratins, epithelial membrane antigen (EMA), epithelial antigen Ber-EP4, carcinoembryonic antigen (CEA), tumour-associated glycoprotein (B72.3), LeuM1, vimentin, desmin, epithelial related antigen (MOC-31) and mesothelial cell (HBME-1). Positivity for MOC-31 and Ber-EP4 was found to have the highest nosologic sensitivity (94.1% and 84.6%, respectively) and specificity (86.3% both antibodies) for carcinoma. Positive staining for HBME-1 and vimentin had the highest sensitivity (90.9% and 100%, respectively) and specificity (91.3% and 60%, respectively) for mesothelioma. A two-marker antibody panel with HBME-1 and MOC-31 was the most efficient for the distinction between carcinoma and malignant pleural mesothelioma.

CONCLUSION

A combination of MOC-31 (an anti- epithelial marker) and HBME-1 (an anti-mesothelial marker) has a diagnostic efficiency of 76.1% for the distinction between carcinoma and mesothelioma in pleura.

Calretinin and other mesothelioma markers in synovial sarcoma: analysis of antigenic similarities and differences with malignant mesothelioma

Synovial sarcoma (SS) is a mesenchymal neoplasm that typically shows epithelial differentiation. SS commonly metastasizes to lung and pleura, and has also been reported as the primary in these locations. The histologic distinction of SS from mesothelioma may be difficult because of the combination of epithelioid and spindle cells, potentially shared locations, and antigenic expression. In this study the authors examined 103 well-documented SSs including 41 biphasic, 44 monophasic, and 18 poorly differentiated SSs in comparison with 23 epithelioid and seven sarcomatous mesotheliomas. Most biphasic SSs (29 of 41, 71%) had fields or foci of calretinin-positive tumor cells. The spindle cell components were more often positive (55%), whereas 14% of tumors had positive epithelial cells. The monophasic and poorly differentiated SSs commonly had foci of calretinin-positive cells (in 52% and 56% of cases respectively). In comparison, all 23 epithelioid mesotheliomas (EM) were extensively calretinin positive and seven sarcomatoid mesotheliomas were variably calretinin positive. HBME-1 positivity was similarly detected in biphasic SS and EM (100% and 87% respectively). Among the other sarcomas, two of 15 malignant peripheral nerve sheath tumors were focally calretinin positive, whereas 16 epithelioid sarcomas, 20 leiomyosarcomas, 20 gastrointestinal stromal tumors, and 20 angiosarcomas were negative. Biphasic SSs differed from mesotheliomas by their more common BerEp4 positivity (90%) whereas EMs showed focal reactivity in 13% cases. Marked CD15 reactivity was rare in both. Wilms tumor protein-1 (WT1) was not detected in SS, but was present in 12 of 17 EMs. CD141 was rare in SS, limited to spindle cell components, whereas EMs typically showed prominent membrane staining in epithelial cells. Simple epithelial keratins were present in all epithelial cells of biphasic SS and mesothelioma (keratin 7[K7], K19), but were only focal in monophasic and poorly differentiated SS. Biphasic SSs were extensively K14 positive (89% of cases), whereas epithelial and sarcomatoid mesotheliomas typically showed only scattered positive cells. The potentially shared calretinin patterns in SS and mesothelioma require the use of other markers. The discriminating features include extensive BerEp4 positivity, rarity of CD141, and lack of WT1 in SS. Global expression of K7 and K19 in mesotheliomas versus focal expression in monophasic and poorly differentiated SSs, and differential patterns of K14 expression may also be helpful.

Unilocular retroperitoneal cyst of mesothelial origin presenting as a renal mass

We report the first 2 cases, to our knowledge, of retroperitoneal cysts with features of mesothelial differentiation that clinically mimic renal masses. The first lesion occurred in a 71-year-old man who presented with flank pain. Ultrasound and magnetic resonance imaging studies showed a unilocular cystic structure arising from the upper pole of the left kidney. The second lesion was in a 44-year-old woman who presented with left flank pain. Imaging studies revealed an 8-cm hemorrhagic cyst at the lower pole of the left kidney. Histologic examination of the nephrectomy specimens in each case revealed a unilocular cyst with intracystic and pericystic hemorrhage. In each case, the cyst was lined by a single layer of cells with ample eosinophilic cytoplasm and benign nuclear features without mucinous or müllerian differentiation. Histochemical staining showed Alcian blue positivity on the cell surface, which was sensitive to hyaluronidase digestion. Intracytoplasmic mucin, however, was not detected. Immunostaining showed that the cyst lining cells were positive for keratin, vimentin, HBME-1, WT1, and thrombomodulin but negative for carcinoembryonic antigen, B72.3, Leu-M1, and BerEP4. The first case was positive for calretinin, whereas the second was negative. These findings support the mesothelial nature of the cysts.

Utility of surfactant protein B precursor and thyroid transcription factor 1 in differentiating adenocarcinoma of the lung from malignant mesothelioma

Differentiation of malignant mesothelioma from adenocarcinoma, particularly from a lung primary, remains a difficult diagnostic problem. Surfactant protein B precursor (pro-SP-B) and thyroid transcription factor 1 (ITF-1) are expressed selectively in the normal respiratory epithelium and in adenocarcinomas of the lung. In this study, we evaluated the utility of pro-SP-B and ITF-1 in distinguishing pulmonary adenocarcinomas and malignant mesotheliomas. Immunoreactivity for pro-SP-B and TTF-1 was examined in paraffin sections of 370 primary lung carcinomas (208 adenocarcinomas, 101 squamous cell carcinomas, and 61 large cell carcinomas) and 95 malignant mesotheliomas, using a pro-SP-B antiserum and a monoclonal TTF-1 antibody with a biotin-streptavidin detection system. Immunostaining for pro-SP-B was detected in 57% of adenocarcinomas, and 20% of large cell carcinomas. Immunoreactivity for TTF-1 was shown in 76% of adenocarcinomas and 26% of large cell carcinomas. Malignant mesotheliomas and squamous cell carcinomas did not stain with either antibody. The expression of pro-SP-B and TTF-1 in adenocarcinomas of the lung but not in malignant mesotheliomas shows that pro-SP-B and TTF-1 staining is useful in differentiating these neoplasms.

Embolization of mesothelial cells in lymphatics: the route to mesothelial inclusions in lymph nodes?

AIMS

To provide evidence that lymphatic embolization is the mechanism for mesothelial inclusions in lymph nodes.

METHODS AND RESULTS

A 60-year-old man with alcoholic cirrhosis and ascites had an umbilical hernia resected. The herniorrhaphy specimen contained numerous dermal and submesothelial lymphatic vessels filled by cells similar to the cells that lined the hernia sac. Most of the cells in lymphatics were submesothelial reactive cells, whose cytoplasm stained with antibodies against cytokeratins (AE1-AE3; 8, 18), smooth muscle actin, vimentin, desmin and tissue polypeptide antigen (TPA). Some cells seemed to be superficial mesothelial cells, being positive with high molecular weight anticytokeratin antibody 34 beta E12. On ultrastructural study submesothelial cells with intermediate cytoplasmic filaments, rough endoplasmic reticulum and primitive cell junctions, and scanty superficial mesothelial cells with microvilli, tonofilaments and desmosomes were found in the lymphatics.

CONCLUSIONS

Lymphatic dissemination of mesothelial and submesothelial cells is an uncommon and not well known phenomenon. Lymphatic dissemination is probably the route by which the mesothelial cells reach the lymphatic nodes. These cells may be mistaken for malignant cells.