Clear cell mesothelioma

Clear cell mesotheliomas with inactivating VHL mutations and near-haploid genomic features

Clear cell mesothelioma is uncommon and shows predominance of clear cells with resemblance to clear cell carcinomas. Clinicopathologic and molecular descriptions of clear cell mesothelioma remained limited. In this study, we identified an index patient with clear cell mesothelioma, confirmed by immunohistochemical and ultrastructural studies. Targeted next-generation sequencing revealed the presence of an inactivating VHL mutation. We then systematically searched for VHL-mutant mesotheliomas in a comprehensive genomic profiling database of 1532 mesotheliomas. Collectively, we identified a cohort of four VHL-mutant clear cell mesotheliomas, including three peritoneal and one pleural tumors from three females and one male, with age range of 47-68 (median 63) years. Histologically, each tumor showed a microcystic to tubulopapillary architecture with prominent clear cells. By next-generation DNA sequencing, each of the four clear cell mesotheliomas harbored inactivating VHL mutations, while lacking other alterations typical of mesotheliomas such as BAP1, NF2, SETD2, CDKN2A, CDKN2B, TP53, and PTEN. By using low-pass whole genome sequencing on the index case and targeted next-generation sequencing on the remaining three cases, we identified extensive loss of heterozygosity throughout the genome but consistently sparing chromosomes 5, 7, and 20, characteristic of genomic near-haploidization. In summary, clear cell mesotheliomas were characterized by inactivating VHL mutations and genomic near-haploidization and appeared to represent a distinct clinicopathologic and molecular category of mesotheliomas. Our findings implicate VHL in the pathogenesis of a subset of mesotheliomas, particularly those with clear cell morphology.

Clinicopathological characteristics of primary peritoneal epithelioid mesothelioma of clear cell type: A case report

RATIONALE

Primary peritoneal epithelioid mesothelioma of clear cell type is an extremely rare entity composed of clear cytoplasm. It is challenging to diagnose because of the morphological resemblance to clear cell tumor.

PATIENTS CONCERNS

A 69-year-old male patient had swollen lymph nodes in the right inguinal region for 7 months and was constipated for 1 month.

DIAGNOSIS

The patient was diagnosed as peritoneal epithelioid mesothelioma of clear cell type based on computed tomography scan, pathology, immunohistochemistry, special staining and whole-exome sequencing. This patient harbored VHL gene alteration in exon 1 and homologous recombination defect (with a score of 45). This finding indicated that this patient might be sensitive to platinum-based therapy and Poly ADP-ribose Polymerase (PARP) inhibitor. This patient carried no microsatellite instability, a low level of tumor mutation burden, and a high extent of intratumoral heterogeneity. Eighteen neoantigens were detected.

INTERVENTIONS

The patient received surgery-based multidisciplinary treatment by integrating cytoreductive surgery (CRS) with hyperthermic intraperitoneal chemotherapy (HIPEC). HIPEC was administered with docetaxel 120 mg plus cisplatin 120 mg, at 43°C, for 60 minutes. After operation, the patient received intravenous (IV) chemotherapy with docetaxel 60 mg, pemetrexed 750 mg and cisplatin 100 mg, and then intraperitoneal (IP) chemotherapy with docetaxel 40 mg. The patient received interventional therapy of hepatic artery embolization for 5 times.

OUTCOMES

Regular follow-up was performed until Oct 14, 2020. The patient died 31.6 months later owing to incomplete intestinal obstruction.

LESSONS

Primary peritoneal epithelioid mesothelioma of clear cell type needs to be differentiated from a variety of clear cell tumors. This disease is characterized by specific genetic alteration. Whole-exome sequencing contributes to guide individualized therapy. CRS-HIPEC helps achieve long-term overall survival.

Guidelines for Pathologic Diagnosis of Malignant Mesothelioma 2017 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 and expertise in the field contributed to this update. Reference material included up-to-date, peer-reviewed publications and textbooks.

CONCLUSIONS

- There was discussion and consensus opinion regarding guidelines for (1) distinguishing benign from malignant mesothelial proliferations (both epithelioid and spindle cell lesions), (2) cytologic diagnosis of MM, (3) recognition of the key histologic features of pleural and peritoneal MM, (4) use of histochemical and immunohistochemical stains in the diagnosis and differential diagnosis of MM, (5) differentiating epithelioid MM from various carcinomas (lung, breast, ovarian, and colonic adenocarcinomas, and squamous cell and renal cell carcinomas), (6) diagnosis of sarcomatoid MM, (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 employed is dependent on the differential diagnosis and on the antibodies available in a given laboratory. Depending on the morphology, immunohistochemical panels should contain both positive and negative markers for mesothelial differentiation and for lesions considered in the differential diagnosis. Immunohistochemical markers should 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 and membranous markers). Selected molecular markers are now being used to distinguish benign from malignant mesothelial proliferations. These guidelines are meant to be a practical diagnostic reference for the pathologist; however, some new pathologic predictors of prognosis and response to therapy are also included.

Mesothelioma with signet-ring cell features: report of 23 cases

Signet-ring cell mesothelioma is uncommon and only two case reports have been published on this mesothelioma variant, both of which were initially misdiagnosed as signet-ring cell carcinoma. Herein are reported 23 signet-ring cell mesotheliomas that were investigated by immunohistochemistry, 12 of which were also studied by electron microscopy. Twenty-one of the cases originated in the pleura and two in the peritoneum. For comparison purposes and in order to determine the value of these techniques in the differential diagnosis of these tumors, seven cases of signet-ring cell lung adenocarcinoma were also studied. All signet-ring cell mesotheliomas were positive for calretinin, keratin 5/6, keratin 7, and mesothelin, 93% for podoplanin, and 91% for WT1; whereas, none reacted for MOC-31, CEA, TAG-72, CD15, TTF-1, napsin A, or CDX2. Among signet-ring cell lung adenocarcinomas, 100% were positive for keratin 7, CEA, and napsin A, 86% each for TTF-1 and TAG-72, 71% for CD15, and 14% for mesothelin, while all were negative for calretinin, keratin 5/6, WT1, podoplanin, and CDX2. After analyzing the results, it is concluded that the panels of markers used in the differential diagnosis of this mesothelioma variant should include those markers that are usually expressed in mesotheliomas (eg, calretinin, keratin 5/6, WT1, and podoplanin), broad-spectrum carcinoma markers that are frequently expressed in adenocarcinomas regardless of their site of origin (eg, MOC-31 and CEA), and organ-associated markers (eg, TTF-1 and napsin A for lung), which allow the site of origin of a metastatic adenocarcinoma to be established. Electron microscopy can be very useful as it permits the identification of characteristic ultrastructural mesothelioma and adenocarcinoma markers, and it also allows a better understanding of the morphologic features seen on routine light microscopy. Pathologists should be aware of this mesothelioma subtype as it can potentially be confused with other tumors that exhibit signet-ring features.

Deciduoid mesothelioma: report of 21 cases with review of the literature

Deciduoid mesothelioma is a rare variant of epithelioid mesothelioma that was initially considered to occur exclusively in the peritoneum of young women who had no history of asbestos exposure and to be characterized by an aggressive clinical course, but it was later demonstrated that this tumor could also occur in the pleura of older men and women who had been exposed to asbestos. Some subsequent studies have also indicated that the clinical course is no different from that of conventional epithelioid mesothelioma. Herein are reported 21 cases of deciduoid mesothelioma that were investigated using a large panel of immunohistochemical markers, 9 of which were also studied by electron microscopy. Fifteen of the patients were male and 6 were female (mean age, 60 years). Seventeen of the cases originated in the pleura and four in the peritoneum. Histologically, all of the cases were composed of large, polygonal or ovoid cells with well-defined cell borders, dense eosinophilic cytoplasm, and single or multiple nuclei. In some cases, the cells exhibited a wide variation in their size and shape, frequent loss of cell cohesion, marked nuclear atypia, and high mitotic activity (>5 per 10 HPF); whereas, in others, the cells were more cohesive, less pleomorphic, and the mitotic activity low. As the survival of patients in the first group of cases was shorter (mean, 7 months), when compared with that of the latter (mean, 23 months), it is concluded that the differences in prognosis reported in deciduoid mesothelioma are due to the existence of a high-grade subgroup that presents highly aggressive clinical behavior. Therefore, when a high-grade deciduoid mesothelioma is present, it should be reported as it can significantly affect prognosis and treatment. The use of immunohistochemistry and electron microscopy in assisting in the differential diagnosis of deciduoid mesothelioma is also discussed.

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.

Pleomorphic mesothelioma: report of 10 cases

Mesotheliomas with pleomorphic features are rare and only a few studies on this mesothelioma variant have been published. Little information regarding the immunoprofile of these tumors and none on their electron microscopic features was included in these studies. Herein are reported 10 cases of pleomorphic mesothelioma that were investigated using a large panel of immunohistochemical markers, 4 of which were also studied by electron microscopy. All of the patients were men and seven had a history of asbestos exposure. Nine of the cases originated in the pleura and one in the peritoneum. Histologically, the tumors were characterized by being composed of large, often discohesive, cells that varied in size and shape, had dense abundant eosinophilic cytoplasm, and single or multiple irregular nuclei, which often contained one or several large nucleoli. Mitotic activity was high and atypical mitoses frequent. Immunoreactivity for pan-keratin and keratin 7 was strong in all of the cases. Expression for calretinin, WT1, podoplanin, mesothelin and keratin 5/6 was also frequent, but variable. All cases were negative for MOC-31, carcinoembryonic antigen, CD15, TAG-72 and thyroid transcription factor-1. Electron microscopy often showed the presence of abundant long, slender microvilli on the cell membrane of the neoplastic cells. These findings demonstrate that, contrary to what has been suggested by some investigators, both immunohistochemistry and electron microscopy can be very helpful in assisting in the diagnosis of pleomorphic mesotheliomas. That the seven patients who underwent extrapleural pneumonectomy had extensive lymph node metastasis and that the median survival of those patients for whom follow-up information was available was only 8.2 months indicates that mesotheliomas with pleomorphic features are associated with highly aggressive clinical behavior. Therefore, when this subtype of epithelioid mesothelioma is present, it should be reported as it can significantly affect the prognosis and treatment of the patient.

Mesotheliomas with small cell features: report of eight cases

Mesotheliomas with small cell morphology are rare and only one study of such cases has been published. As a result of their rare occurrence, some investigators have cast doubt on the existence of such a histologic variant of mesothelioma. This investigator reports a series of eight cases of epithelioid mesothelioma with small cell features, all of which originated in the pleura. Seven of the patients were men and one was a woman. Four patients had a history of asbestos exposure. Histologically, four of the mesotheliomas were epithelioid and four biphasic. The proportion of small cells seen in these cases constituted 80 to 100% of the tumor included in the biopsy material and 15 to 20% of the tumor present in the pneumonectomy specimens. Immunoreactivity for calretinin, keratin 5/6, keratin 7, pan-keratin, WT1, podoplanin, and mesothelin was seen in all cases tested for these markers. All of the cases were negative for MOC-31, Ber-EP4, CEA, CD15, TAG-72, TTF-1, chromogranin A, synaptophysin, CD99, and desmin. The mean survival of the six patients for whom this information was available was 8.2 months. It is important for pathologists to be aware that mesotheliomas can present small cell features and, because of this, they can be confused with other malignancies that can exhibit similar morphology. The value of immunohistochemistry in the differential diagnosis of these tumors is discussed.

Primary pleural epithelioid mesothelioma of clear cell type: a case report and review of current literature

Primary pleural epithelioid mesothelioma with clear cell morphology is a particularly rare neoplasm, with only a few documented cases. Here, the authors report a case of a 76-year-old man, with a history of asbestos exposure, admitted for mild dyspnea. Radiologic examination revealed right pleural effusion and pleural thickening. Cytological examination of aspirated pleural samples was consistent with non-small cell carcinoma. Histological examination of the resected, via VATS, plural specimens was consistent with the diagnosis of clear cell epithelioid mesothelioma. The authors further analyze the main morphological and immunohistochemical features of clear cell epithelioid mesothelioma, emphasizing the algorithm for excluding other clear cell tumors metastatic to the pleura.

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

CONTEXT

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

OBJECTIVE

To develop practical guidelines for the pathologic diagnosis of MM.

DATA SOURCES

A pathology panel was convened at the International Mesothelioma Interest Group biennial meeting (October 2006). Pathologists with an interest in the field also contributed after the meeting.

CONCLUSIONS

There was consensus opinion regarding (1) distinguishing 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) differentiating 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 differential 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. The International Mesothelioma Interest Group recommends that 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.

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.

Expression of renal cell carcinoma-associated markers erythropoietin, CD10, and renal cell carcinoma marker in diffuse malignant mesothelioma and metastatic renal cell carcinoma

CONTEXT

Metastatic renal cell carcinoma (MRCC) involving the thorax can be difficult to distinguish from diffuse malignant mesothelioma (DMM) using traditional morphologic approaches. Standard panels of immunohistochemical markers are of limited benefit.

OBJECTIVE

To investigate several antibodies to renal cell carcinoma-associated proteins for differentiating MRCC from DMM.

DESIGN

One hundred DMMs and 20 MRCCs were evaluated for immunoexpression of erythropoietin. The same cases and an additional 45 DMMs were evaluated for CD10 and renal cell carcinoma marker (RCCMa) immunoreactivity.

RESULTS

Erythropoietin was expressed in 100% of DMMs and MRCCs. Staining for CD10 was observed in 54% of DMMs and 100% of MRCCs. RCCMa stained 26% of DMMs and 55% of MRCCs. Although erythropoietin staining was similarly strong and diffuse in both DMM and MRC, patterns of staining for RCCMa and CD10 differed between MRCC and DMM. Immunoreactivity was strong and diffuse for both RCCMa and CD10 in most MRCCs. Of CD10-positive DMMs, nearly half showed staining in less than 50% of tumor cells and about one fourth of positive cases exhibited only weak to moderately intense staining. Only half of RCCMa-positive DMMs showed staining in more than 49% of tumor cells and staining was only weak to moderately intense in most cases.

CONCLUSIONS

Given the overlap in the expression of renal cell carcinoma markers in MRCC and DMM, results with these markers must be interpreted cautiously and should be used in conjunction with mesothelium-associated markers. Differences in expression may potentially help distinguish MRCC from DMM inasmuch as strong and diffuse expression of RCCMa and CD10 supports a diagnosis of MRCC over DMM.

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.

Mesothelioma with clear cell features: an ultrastructural and immunohistochemical study of 20 cases

Mesotheliomas with clear cell morphology are rare and only a few individual case reports have been documented in the literature. The author reports a series of 20 epithelioid mesotheliomas with clear features, 17 of which originated in the pleura and 3 in the peritoneum. Eighteen of the patients were men and 2 were women. Twelve patients had a history of asbestos exposure. Electron microscopy and special histochemical stains demonstrated that the cytoplasmic clearing seen in hematoxylin and eosin-stained sections resulted from multiple factors that can occur either singly or in combination. The most frequent cause of the cytoplasmic clearing was the accumulation of large amounts of intracytoplasmic glycogen. Another but somewhat less common factor was the accumulation of large amounts of lipid, which occurred alone or with glycogen. Other less common causes were marked mitochondrial swelling, the presence of numerous intracytoplasmic vesicles, and a large number of intracytoplasmic lumens. The value of immunohistochemistry in helping to distinguish epithelioid mesotheliomas from some carcinomas with clear cell morphology is emphasized. In addition, it was determined that because electron microscopy was decisive in establishing the cause of the cytoplasmic clearing in most of the cases, tissue for electron microscopy should routinely be procured for ultrastructural studies.

Clear cell mesothelioma presenting as an incarcerated abdominal hernia

A clear cell mesothelioma presenting as an incarcerated ventral abdominal hernia in a 67-year-old man who had no history of asbestos exposure is described. The cause of the cytoplasmic clearing was the presence of large amounts of glycogen. Although uncommon, this variant of mesothelioma is important to recognize because it can be easily confused with other clear cell tumors involving the serosal membranes. Significant recent advances in the immunohistochemistry of epithelioid mesothelioma are briefly reviewed because immunohistochemical studies can be helpful in establishing the correct diagnosis.

The diagnostic utility of immunohistochemistry in distinguishing between mesothelioma and renal cell carcinoma: A comparative study

Both mesotheliomas and renal cell carcinomas can present a wide variety of morphological patterns. Because of this, renal cell carcinomas that metastasize to the pleura and lung may be confused with mesotheliomas. The aim of the present study was to compare the value of the various immunohistochemical markers currently available for the diagnosis of mesothelioma and renal cell carcinoma. A total of 48 mesotheliomas (40 epithelioid, 8 sarcomatoid), and 48 renal cell carcinomas (24 conventional, 12 chromophobe, 8 papillary, 4 sarcomatoid) were investigated for the expression of the following markers: calretinin, mesothelin, cytokeratin 5/6, WT1, thrombomodulin (TM), N-cadherin, CD15 (leu-M1), MOC-31, Ber-EP4, BG-8 (Lewis(y)), CD10, renal cell carcinoma marker (RCC Ma), carcinoembryonic antigen (CEA), and B72.3. All (100%) of the epithelioid mesotheliomas reacted for calretinin, mesothelin, and cytokeratin 5/6; 93% for WT1; 78% for TM; 75% for N-cadherin, 48% for CD10, 15% for Ber-EP4, 8% for MOC-31, 8% for RCC Ma, 5% for BG-8, and none for CEA, B72.3, or CD15. Of the sarcomatoid mesotheliomas, 88% expressed calretinin, 75% N-cadherin, 38% CD10, and 13% each expressed cytokeratin 5/6, WT1, and TM. All of the remaining markers were negative. Among the RCCs, 81% expressed CD10, 75% N-cadherin, 63% CD15, 50% RCC Ma, 50% MOC-31, 42% Ber-EP4, 8% BG-8, and 2% TM. The remaining markers were negative. The results indicate that calretinin, mesothelin, and cytokeratin 5/6 are the best positive mesothelioma markers for differentiating epithelioid mesotheliomas from renal cell carcinomas. The best discriminators among the antibodies considered negative markers for mesothelioma are CD15, MOC-31, and RCC Ma. An accurate differential diagnosis can be reached with the use of any 2 of the 3 recommended positive markers, which should be selected based on availability and on which ones yield the best staining results in a given laboratory. One of the recommended negative markers may be added to the panel if deemed necessary. If confirmation of renal origin is needed, RCC Ma could be useful. Calretinin is the only marker that appears to have any utility in distinguishing between sarcomatoid mesotheliomas and sarcomatoid renal cell carcinomas.

The value of 'mesothelium-associated' antibodies in distinguishing between metastatic renal cell carcinomas and mesotheliomas

AIMS

Despite increasing usage of mesothelium-associated antibodies in diagnosis, a meta-analysis of studies analysing these antibodies in relation to distinguishing mesothelioma from renal cell carcinoma shows a paucity of published data. Given the clinical importance of elucidating this differential diagnosis, we compared the phenotypes of these two tumours using a panel of antibodies comprising recently described 'mesothelium-associated' antibodies and the more established 'epithelium-associated' antibodies.

METHODS AND RESULTS

We applied an antibody panel comprising calretinin, cytokeratin (CK)5/6, thrombomodulin, carcinoembryonic antigen (CEA), BerEP4 and BCA225 to 37 cases of pleural mesotheliomas and 40 cases of renal cell carcinoma (27 primary tumours and 13 metastatic to the pleura). All mesotheliomas were either purely epithelioid or of mixed type. Cases of renal cell carcinoma were graded and classified as to cell type and architecture. For mesotheliomas, 0% stained for CEA, 16% for BerEP4, 83% for BCA225, 78% for CK5/6, 86% for thrombomodulin and 97% showed nuclear staining for calretinin. For renal cell carcinomas, 0% stained for CEA, 50% for BerEP4, 88% for BCA225, 5% for CK5/6, 32% for thrombomodulin and 10% showed nuclear staining for calretinin.

CONCLUSION

Calretinin, CK5/6 and BerEP4 appear the most useful antibodies in helping to distinguish between renal cell carcinomas and mesotheliomas, although BerEP4 was not particularly sensitive for renal cell carcinomas. Thrombomodulin was not as specific as the other 'mesothelium-associated' antibodies in this study, reflecting how staining for mesothelium-associated antibodies varies in carcinomas from different primary sites, and such variations should be taken into account when assessing the differential diagnosis of mesothelioma. In cases where doubt remains over distinguishing metastatic renal cell carcinoma from mesothelioma, data from such a panel should be viewed with caution and assessed in association with clinical, imaging and morphological features.

Unusual clear cell variant of epithelioid mesothelioma

Clear cell mesothelioma is an extremely rare neoplasm of the pleura, which can easily be mistaken for a metastasis of clear cell carcinoma to the pleura. We report here the histochemical, immunohistochemical, and ultrastructural aspects of a new case of clear cell pleural mesothelioma in a 52-year-old man with no known asbestos exposure. He was admitted to the hospital for recurrent pleural effusion, which was negative for neoplastic cells at the cytologic examination. A partial decortication of the right pleura was performed. The morphologic, immunohistochemical, and ultrastructural features reported for this case are consistent with the diagnosis of clear cell mesothelioma. The differential diagnosis and immunohistochemical features in comparison with other clear cell neoplasms are discussed.

Epithelial mesothelioma with deciduoid features: report of four cases

Deciduoid mesothelioma is the designation given to an unusual morphologic variant of epithelial mesothelioma that closely simulates exuberant ectopic decidual reaction. Because all four previously reported cases involved the peritoneum and occurred in young women without a history of asbestos exposure, it was suggested that deciduoid mesothelioma was a subtype of epithelial mesothelioma characterized by its unique morphology, that it affects a distinct patient population, and that it is unrelated etiologically to asbestos. The author reports four cases of mesothelioma with deciduoid features, all of which originated in the pleura. Three of the patients were men and one was a woman. Their ages ranged from 46 to 78 years (mean age, 67 yrs). Two of the patients had a history of asbestos exposure. These findings indicate that this morphologic variant of mesothelioma is not limited to a specific patient population nor is it restricted to the peritoneum.

Pulmonary clear cell carcinoid tumor: another entity in the differential diagnosis of pulmonary clear cell neoplasia

A clear cell variant of primary pulmonary carcinoid tumor is described. The tumor arose in a 53-year-old woman who was incidentally found to have a solitary pulmonary nodule in the left upper lobe during routine chest roentgenography. Histologically, the tumor was composed of predominantly clear to lightly eosinophilic, polygonal cells with bland nuclei arranged in sheets and nests. Nuclear pleomorphism, necrosis, vascular invasion, and mitotic figures were not seen. The tumor cells were negative for oil-red-O and periodic acid-Schiff stains with and without diastase pretreatment on frozen and formalin-fixed sections, respectively. During immunohistochemical evaluation, the tumor cells were focally positive for cytokeratin and diffusely positive for neuron-specific enolase and chromogranin. Electron microscopy performed on paraffin block-retrieved tissue showed the presence of electron-dense, neurosecretory-type granules and variably sized vacuolated areas within the cytoplasm. the nature of which remained unclear. Intracytoplasmic glycogen or lipid were not identified. To our knowledge, this is the first report of pulmonary clear cell carcinoid tumor.