Desmin and neural marker expression in mesothelial cells and mesotheliomas

Mesothelial cyst of uterus in a nullipara patient: A case report

INTRODUCTION

Uterine mesothelial cysts represent a diagnostic challenge because of their low incidence, with very few cases reported in the English literature.

PATIENT CONCERNS

We report the case of a 27-year-old nullipara woman complaining of self-discovery of a mass in the abdomen for 1 week. Supersonic examination revealed a pelvic cystic lesion measuring 8.9 × 8.2 cm. The patient underwent exploratory single-port laparoscopic surgery and had a large uterine cystic mass located within the posterior wall of the uterus.

DIAGNOSIS

After excision of the uterine cyst, the final histopathological diagnosis was uterine mesothelial cyst.

INTERVENTIONS

We treated her with a single-port laparoscopic uterine cystectomy.

OUTCOMES

Close follow-up of the case for 2 years showed that the patient was free of any symptoms, and no recurrence was noted.

LESSONS

Uterine mesothelial cysts are extremely rare. They are often misdiagnosed by clinicians as extrauterine masses or cystic degeneration of leiomyomas. This report aims to share a rare case of uterine mesothelial cyst and improve gynecologists' academic vision of the disease.

Malignant mesothelioma in situ: diagnostic and clinical considerations

In situ stages of malignancy have been characterised in various neoplasms. Mesothelioma in situ (MIS) has been a controversial diagnosis, lacking clear diagnostic criteria and understanding as to whether it is truly a premalignant lesion in the progression of malignant mesothelioma (MM). Originally understood as a concept and defined as atypical mesothelial proliferation in the presence of invasion, it has now been suggested that loss of nuclear labelling for BRCA1-associated protein-1 (BAP1) in flat, non-invasive mesothelial lesions can define MIS. This study aimed to characterise BAP1 expression in a cohort of 19 patients diagnosed with MIS (either pure MIS, n=3, or MIS-predominant invasive MM, n=16) and to compare survival between MIS, MIS-predominant MM and MM (n=114) in order to gain insight into the characteristics of MIS. We defined pure MIS as any architectural pattern of surface mesothelial cells with loss of BAP1 in the absence of invasion, but in specimens with superficial stromal invasion we also accepted the original definition of cytologically and architecturally atypical mesothelial proliferation, in the absence of inflammatory features, with or without loss of BAP1. We observed that MIS associated with minimal invasion was associated with significantly improved survival compared to MM (8 months vs 22 months). This suggests that MIS is indeed a precursor to MM and that these cases represent earlier stage disease. Loss of BAP1 was present in 60% of mesotheliomas with invasion, so not all early cases can be detected by BAP1 loss, but our study provides evidence that BAP1 loss may be an early molecular alteration in MM pathogenesis in patients that have loss of BAP1. We confirm that BAP1 loss can be useful for diagnosis of pure MIS in surgical specimens, permitting earlier diagnosis. However, identification of a predominant MIS component with minimal invasion has prognostic and conceptual implications. Whilst no approved therapy is available for MIS, close follow up of patients with BAP1 mutation in mesothelial cells and/or diagnosis of MIS is required to monitor for disease progression and potentially investigate earlier treatment interventions.

Mesenchymal chondrosarcomas showing immunohistochemical evidence of rhabdomyoblastic differentiation: a potential diagnostic pitfall

The diagnosis of mesenchymal chondrosarcoma, a distinctive biphasic malignant neoplasm harboring the HEY1-NCOA2 gene fusion and consisting of primitive round to spindled cells admixed with foci of relatively mature hyaline cartilage, is usually straightforward by morphologic evaluation alone. However, in the setting of a limited biopsy, specimens lacking cartilage generate a broad differential diagnosis, encompassing a variety of other primitive sarcomas, including spindle cell/sclerosing rhabdomyosarcoma. Although a small number of cases of mesenchymal chondrosarcoma with aberrant skeletal muscle marker expression have been reported, pathologists are largely unaware of this potential diagnostic pitfall. We report 6 additional cases of mesenchymal chondrosarcoma showing expression of multiple skeletal muscle markers, including one case initially misdiagnosed as "spindle cell/sclerosing rhabdomyosarcoma" on needle biopsy. Awareness of this phenomenon and judicious application of molecular diagnostic testing for the HEY1-NCOA2 fusion are critical to avoid misclassification of mesenchymal chondrosarcoma as rhabdomyosarcoma, with potentially adverse patient impact.

Sister Mary Joseph nodule caused by metastatic desmoplastic small round cell tumor: A clinicopathological report

Sister Mary Joseph nodule is an uncommon metastatic intra-abdominal malignancy involving the umbilicus. The present study describes a rare case of desmoplastic small round cell tumor (DSRCT), histological grade 3, high grade, Gilly classification 4, stage IV, in an 18-year-old Thai man presenting with the Sister Mary Joseph nodule, ascites and pleural effusion. The histopathological examination of the umbilical mass revealed the presence of malignant small round cells associated with prominent stromal desmoplasia. Immunohistochemical stains showed positive reactivity to cytokeratin, desmin, neuron-specific enolase, Wilms' tumor 1, CD56, CD99 and SWI/SNF-related matrix-associated actin-dependent regulator of chromatin subfamily B member 1 (SMARCB1)/INI1 in the small round cells. Fine needle aspirations of the ascitic fluid and pleural effusion were performed, and immunocytochemistry revealed a metastatic DSRCT. The patient received a VDC/IE regimen of chemotherapy, comprising vincristine, doxorubicin, and cyclophosphamide alternating with ifosfamide and etoposide; however, the patient developed systemic metastasis and succumbed to the disease 6 months later.

Using of immunocytochemistry in differential diagnosis of neoplasms of serosal cavities in dogs

The presence of tumor within the serosal cavities, often connected with accumulation of serosal effusion, is a quite common problem in the small animal veterinary medicine. The first step in diagnosis of such cases is cytopathological examination. The aim of the present study was to evaluate the usefulness of cytology and immunocytochemistry, using commercially available antibodies (anti-cytokeratin, anti-vimentin, and anti-desmin), in differential diagnosis of malignant tumors located within serosal cavities in dogs. The final cytological diagnosis of carcinoma/adenocarcinoma, sarcoma, and mesothelioma was obtained on the basis of routine cytopathology and immunocytochemistry, and then confirmed by histopathology and immunohistochemistry. Cytoplasmic immunoreactivitiy of normal mesothelid cells and cytoplasmic immunoreactivity of hyperplastic mesothelial cells revealed constant and strong expression of all examined intermediate filaments: cytokeratin, vimentin and desmin. Application of routine cytopathology and immunocytochemistry allowed 32 neoplastic tumors to be detected: 19 cases of carcinomas/adenocarcinomas, 6 cases of sarcomas, 7 cases of mesotheliomas. Immunostaining of cytopathological samples with chosen set of antibodies: anti-cytokeratin, anti-vimentin, anti-desmin is a useful, and low invasive test for differentiation between mesotheliomas and carcinomas/adenocarcinomas in dogs.

Desminopathies: pathology and mechanisms

The intermediate filament protein desmin is an essential component of the extra-sarcomeric cytoskeleton in muscle cells. This three-dimensional filamentous framework exerts central roles in the structural and functional alignment and anchorage of myofibrils, the positioning of cell organelles and signaling events. Mutations of the human desmin gene on chromosome 2q35 cause autosomal dominant, autosomal recessive, and sporadic myopathies and/or cardiomyopathies with marked phenotypic variability. The disease onset ranges from childhood to late adulthood. The clinical course is progressive and no specific treatment is currently available for this severely disabling disease. The muscle pathology is characterized by desmin-positive protein aggregates and degenerative changes of the myofibrillar apparatus. The molecular pathophysiology of desminopathies is a complex, multilevel issue. In addition to direct effects on the formation and maintenance of the extra-sarcomeric intermediate filament network, mutant desmin affects essential protein interactions, cell signaling cascades, mitochondrial functions, and protein quality control mechanisms. This review summarizes the currently available data on the epidemiology, clinical phenotypes, myopathology, and genetics of desminopathies. In addition, this work provides an overview on the expression, filament formation processes, biomechanical properties, post-translational modifications, interaction partners, subcellular localization, and functions of wild-type and mutant desmin as well as desmin-related cell and animal models.

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.

Pathohistological diagnosis and differential diagnosis

Malignant mesothelioma is a rare aggressive tumour arising from mesothelial cells of the pleural and peritoneal cavity including pericardium and tunica vaginalis testis. Malignant mesothelioma occurs predominantly in men (>90%). Asbestos exposure is the best known and evaluated risk factor with a long latency period between exposure and onset of malignant mesothelioma ranging from 15 to 60 years. Exposure to erionite leads to higher incidences of mesothelioma and play an important role in environmental exposure (Turkey). Other possible risk factors are radiation, recurrent pleuritis/peritonitis and simian virus 40 (SV 40).Malignant pleural mesothelioma is most common, whereas malignant peritoneal mesothelioma accounts only for 6-10%. Infrequent sites of origin are the pericardium and tunica vaginalis in 1-2%.Malignant mesothelioma shows either diffuse growth pattern or occurs as a localised tumour mass. Diffuse type represents an aggressive tumour with poor prognosis and is incurable in most cases.According to the WHO classification, three histological subtypes are distinguished: epithelioid, sarcomatoid and biphasic malignant mesothelioma.Rare variants are desmoplastic type, a subtype of sarcomatoid mesothelioma, undifferentiated type and deciduoid type. Epithelioid type is the most frequent one, but biphasic malignant mesothelioma occurs in 30%. Pure sarcomatoid or biphasic type is seen less frequently in malignant peritoneal mesothelioma than in its pleural counterpart.Well-differentiated papillary mesothelioma is a generally non-invasive mesothelioma with low malignant potential that arises mostly in females in the peritoneal cavity. Histological type is an important prognostic marker. Longest survival is seen in patients with epithelioid malignant mesothelioma. Sarcomatoid subtype has the worst prognosis.Malignant mesothelioma shows macroscopical and microscopical similarities to benign lesions and other malignancies. Therefore, reactive mesothelial proliferations on the one hand and secondary tumours resembling mesothelial cells as well as benign or rare mesothelial tumours on the other hand have to be distinguished. Additional immunohistochemistry is essential in histopathological assessment using a marker panel of antibodies.

Immunocytochemistry of CD146 is useful to discriminate between malignant pleural mesothelioma and reactive mesothelium

Malignant pleural mesothelioma is a refractory tumor with poor prognosis associated with asbestos exposure. Pleural effusion is frequently observed in patients with malignant pleural mesothelioma, and cytological analysis is effective to detect malignant pleural mesothelioma. However, cytological discrimination between malignant pleural mesothelioma and reactive mesothelium is often difficult. Increased expression of CD146, a cell adhesion molecule, has been reported to be closely associated with an advanced stage of malignant melanoma, prostate cancer, and ovarian cancer. In this study, to evaluate the diagnostic utility of CD146 for discrimination between malignant pleural mesothelioma and reactive mesothelium, we examined immunocytochemical expression of CD146 in malignant pleural mesothelioma and reactive mesothelium using two clones of CD146 antibody, OJ79 and EPR3208, on smear specimens of effusion fluids. Immunocytochemical stains were semiquantitatively scored on the basis of immunostaining intensity (0, negative; 1, weak positive; 2, moderate positive; and 3, strong positive). CD146 expression was detected in 15 of 16 malignant pleural mesothelioma with median immunostaining score of 3 by OJ79, and in 19 of 21 malignant pleural mesothelioma with median immunostaining score of 2 by EPR3208. Strong immunoreactivity of CD146 was observed at the apposing surfaces of cell-cell interactions on the plasma membrane of mesothelioma cells. In addition, one OJ79-negative case of malignant pleural mesothelioma was positive for CD146 by EPR3208 and two EPR3208-negative cases of malignant pleural mesothelioma were CD146 positive by OJ79, showing that all 23 malignant pleural mesothelioma cases were positive for CD146 by either OJ79 or EPR3208. On the other hand, CD146 expression was undetectable in all reactive mesothelium cases by OJ79 and EPR3208. The sensitivity of OJ79 and EPR3208 was 94 and 90%, respectively, and the specificity was 100% for both clones. We propose that CD146 is a sensitive and specific immunocytochemical marker enabling differential diagnosis of malignant pleural mesothelioma from reactive mesothelium.

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.

Pathology of mesothelioma

The incidence of mesothelioma has been gradually increasing in Japan, and the underlying factor for this is considered to be the increase in the amount of asbestos imported into Japan between 1960 and 1975. Mesothelioma can be roughly divided into localized and diffuse types, but the former is extremely rare. In making a diagnosis of mesothelioma, it is important to confirm the location of tumor and the specific gross findings before histological examination. Mesothelioma can be categorized histologically as epithelioid type, sarcomatoid type, biphasic type, desmoplastic type, among others. It can take many forms; consequently, there are many diseases to be differentiated when the diagnosis of mesothelioma is based on histological analyses. Immunohistochemical stains are useful for making a diagnosis, but the correct combination of antibodies as positive or negative markers should be selected and a comprehensive assessment of the staining results is necessary. The accuracy of the pathological diagnosis is very important to the patients because they can be receive official compensation or relief when the diagnosis of mesothelioma is confirmed. Under present conditions, both clinicians and pathologists must make a concerted effort to improve the accuracy of the diagnosis of mesothelioma.

Best practices in diagnostic immunohistochemistry: pleomorphic cutaneous spindle cell tumors

CONTEXT

Pleomorphic cutaneous spindle cell tumors can be difficult to distinguish solely on histologic grounds. The use of ancillary immunohistochemical studies can greatly assist in this differential diagnosis.

OBJECTIVE

To review histologic and immunohistochemical aspects of cutaneous spindle cell tumors and discuss a basic panel of markers to assist in the differential diagnosis.

DATA SOURCES

English-language literature published between 1981 and 2005.

CONCLUSIONS

A basic immunohistochemistry panel for high-molecular-weight cytokeratin, melanocytic markers (S100 protein, HMB-45, Melan-A), smooth muscle actin, desmin, and endothelial markers (CD31, CD34) is effective in diagnosing most cutaneous spindle cell tumors.

Sensitivity and specificity of immunohistochemical antibodies used to distinguish between benign and malignant pleural disease: a systematic review of published reports

AIMS

A systematic review of published reports that have evaluated the ability of immunohistochemistry and argyrophil nucleolar organizing region (AgNOR) staining to distinguish between benign and malignant pleural disease.

METHODS

Nineteen relevant papers published during the period 1979-2005 were identified. Individual results of immunohistochemistry for five diagnostic antibodies were extracted to calculate diagnostic sensitivity and specificity. results from five of these studies that had evaluated proliferation markers or AgNOR staining techniques were also summarized.

RESULTS

Most antibodies demonstrated poor to moderate diagnostic ability. Desmin and epithelial membrane antigen (EMA) were the most useful, with sensitivity and specificity both above 74%. The combination of EMA and AgNOR was reported as having 95% diagnostic sensitivity. A high MCM2 labelling index also differentiated between benign and malignant pleural disease.

CONCLUSIONS

Immunohistochemistry is of limited value, but newer diagnostic methods may be useful additions in this area of pathology. The diagnostic importance of histological features seen on plain tissue sections is emphasized as vital for correctly differentiating between benign pleural disease and malignant pleural mesothelioma.

What are the current best immunohistochemical markers for the diagnosis of epithelioid mesothelioma? A review and update

Numerous immunohistochemical markers that can assist in the diagnosis of epithelioid mesotheliomas, some of which have only recently been recognized, are currently available. Because the various types of carcinomas express these markers differently, their selection for inclusion in a diagnostic panel can vary according to the differential diagnosis. This article provides a critical review of all of the information that is presently available on those markers that are believed to have the greatest potential for assisting in distinguishing between epithelioid mesotheliomas and those carcinomas with which they are most likely to be confused. Information is also provided regarding the panels of immunohistochemical markers that are, at present, recommended in these differential diagnoses.

Immunohistochemical Evaluation of Canine Ovarian Tumors

Canine ovarian tumors (epithelial tumor, sex-cord stromal tumor, germ cell tumor) classifying into 9 histological types were examined immunohistochemically using placental alkaline phosphatase (PLAP), cytokeratin7 (CK7), desmin, S100, AE1/AE3, inhibin alpha, vimentin, and alfa feto-protein (AFP). The papillary and tubular types observed in epithelial tumors were immunoreactive for desmin and AE1/AE3. The papillary type was also immunoreactive for PLAP and CK7. The solid type, nest type, cord type, palisade type, cystic type and spindle type, which were observed in sex-cord stromal tumors, showed a positive immunoreaction for S100 but little or no positive immunoreaction for inhibin alpha with an exception of positive result in the palisade type. Most of the sex-cord stromal tumors were AE1/AE3-positive except for the palisade type. In the cobblestone type observed in germ cell tumors, only vimentin and AFP were positive. The present study elucidated the detailed histological and immunohistochemical characteristics of canine ovarian tumors.

Desmoplastic small round cell tumor: Using FISH as an ancillary technique to support cytologic diagnosis in an unusual case

Desmoplastic small round cell tumor is a rare and aggressive neoplasm that predominantly affects young males. In almost all cases, a reciprocal translocation is present resulting in the fusion of the Ewing sarcoma gene with the Wilms' tumor gene. Here we describe an unusual case occurring in a 59-year-old male, in which fluorescence in situ hybridization (FISH) was used in conjunction with immunohistochemical studies to confirm the diagnosis. To our knowledge, this is the first reported case of using FISH as an ancillary technique to confirm the cytologic diagnosis of this tumor.

Applications and limitations of immunohistochemistry in the diagnosis of malignant mesothelioma

Malignant mesothelioma is an uncommon malignant epithelial neoplasm originating from the serosal surface of body cavities. Because serosal surfaces are a common site of metastatic spread for a variety of malignant neoplasms originating from internal organs, separating malignant mesothelioma from metastatic tumors is of clinical importance. The diagnosis of malignant mesothelioma is complex and usually requires a multimodal approach that includes careful clinical history and physical examination, imaging studies, and tissue sampling for multimodal evaluation including routine histology, histochemistry, electron microscopy, and immunohistochemical tests. Of these, immunohistochemistry has emerged as the most valuable and readily available modality for the routine evaluation of these tumors. Unfortunately, no specific antibodies have yet been developed that can be accepted as exclusive for these tumors. The immunohistochemical diagnosis of malignant mesothelioma therefore depends on the use of a panel of stains that includes markers that are commonly expected to react with these tumors ("positive" markers) and markers that are not commonly expected to react with these tumors ("negative" markers). Additionally, the selection and utility of these various markers can vary considerably based on a constellation of circumstances, including patient sex, histologic appearance of the tumor (ie, epithelioid vs. sarcomatoid, etc), and various other clinical circumstances. Herein, we will review the currently available immunohistochemical markers used for the diagnosis of malignant mesothelioma and offer suggestions for the use of appropriate panels of stains based on specific morphologic types and clinical circumstances.

My approach to the diagnosis of mesothelial lesions

Mesothelial lesions pose considerable diagnostic challenges not only because benign tumours, reactive proliferations and malignant mesothelioma can mimic one another, but also because the morphological patterns displayed by malignant mesothelioma can simulate a variety of epithelial and non-epithelial malignancies. Immunohistochemical markers can aid in distinguishing epithelioid malignant mesothelioma from metastatic adenocarcinoma, but because no single marker reliably separates all cases, a panel of stains is recommended. Immunohistochemical studies are of more limited value in sarcomatoid malignant mesothelioma, and other features often play an essential role. The separation of reactive mesothelial proliferations from malignant mesothelioma on small biopsy can be quite difficult, as distinguishing features, such as stromal invasion, often cannot be adequately assessed. In adequately sampled lesions, however, the distinction between malignant mesothelioma, benign mesothelial proliferations and other tumours can be achieved in most cases by using a carefully integrated approach that incorporates clinical and radiographic data, immunohistochemical studies and, in selected cases, histochemical and ultrastructural techniques.

The cardiac isoform of α-actin in regenerating and atrophic skeletal muscle, myopathies and rhabdomyomatous tumors: an immunohistochemical study using monoclonal antibodies

The two sarcomeric isoforms of actins, cardiac and skeletal muscle alpha-actin, are highly homologous so that their immunohistochemical distinction is extremely difficult. Taking advantage of monoclonal antibodies distinguishing the two conservative amino acid exchanges near the aminoterminus, we have performed an extended immunohistochemical analysis of the cardiac alpha-actin (CAA) isoform in normal, regenerating, diseased and neoplastic human muscle tissues. Intense and uniform CAA staining is seen in fetal and adult myocardium and in fetal skeletal muscle while adult skeletal muscle is essentially negative, except for muscle spindle myocytes and a few scattered muscle fibres with overall reduced diameter. By contrast, CAA synthesis is markedly induced in regenerating skeletal muscle cells, in Duchenne muscular dystrophy and upon degenerative atrophy. CAA has also been detected in certain vascular and visceral smooth muscle cells. Among tumors, CAA has consistently been seen in rhabdomyosarcomas and rhabdomyomatous cells of nephroblastomas, whereas, smooth muscle tumors have shown only occasional staining. While the synthesis of this actin isoform is less restricted than previously thought, monoclonal antibodies against CAA provide a well-defined, reliable and sensitive diagnostic tool for the definition and detection of aberrant differentiation in diseased skeletal muscle and of striated muscle differentiation in rhabdomyosarcomas.

Ten cases of feline mesothelioma: an immunohistochemical and ultrastructural study

In the cat only 10 cases of mesothelioma, mainly of the peritoneum, have been previously reported. This paper describes a further 10 cases, eight pleural and two peritoneal, in males and females aged 1-17 years. Histologically, five tumours were epithelial, three fibrosarcomatous and two biphasic. Immunohistochemical markers used in human pathology for the identification of mesotheliomas include vimentin, cytokeratin (CK) AE1/AE3, HBME-1, CK 5/6, calretinin, thrombomodulin, carcinoembryonic antigen (CEA), CD15, E-cadherin and desmin. All 10 feline mesotheliomas were positive for vimentin and CK AE1/AE3, six were positive for HBME-1, two for CK5/6, three for CEA and four for E-cadherin. All were negative for desmin and calretinin. Antibodies to thrombomodulin and CD15 failed to cross-react with feline tissues. Electron microscopy, performed in four cases, revealed microvillar structures, desmosomes and intracytoplasmic lumina, confirming its value as a diagnostic tool. The study showed that mesothelial marker antibodies commonly used in human patients can be used for the diagnosis of feline mesothelioma, preferably as a panel of antibodies rather than only one.

h-Caldesmon, a Useful Positive Marker in the Diagnosis of Pleural Malignant Mesothelioma, Epithelioid Type

Although a large number of immunohistochemical markers that can facilitate the differential diagnosis between epithelioid pleural mesothelioma and lung adenocarcinoma involving the pleura have proven to be valuable, no single antibody has demonstrated absolute sensitivity and/or specificity in making this distinction. Using immunohistochemical analysis with h-caldesmon, a specific marker for smooth muscle tumors, we examined 70 cases of epithelial mesotheliomas and 70 cases of lung adenocarcinomas. In addition, immunohistochemistry for muscle markers, such as desmin, alpha-smooth-muscle actin, muscle-specific actin, myoglobin, myogenin, myosin, and MyoD-1, was performed on all mesothelioma cases. Reactivity for h-caldesmon was obtained in 68 (97%) of the 70 epithelial mesotheliomas, but in none of the adenocarcinoma cases. All mesothelioma cases were found to be negative for the other muscle markers examined. We conclude that h-caldesmon is a highly sensitive and specific marker and suggest its inclusion in the immunohistochemical panel for the differential diagnosis of epithelioid mesothelioma versus lung adenocarcinoma.

Mesothelioma with rhabdoid features: an ultrastructural and immunohistochemical study of 10 cases

Mesotheliomas with rhabdoid morphology are rare and only two individual case reports have been documented in the literature. This author reports a series of 10 cases of mesotheliomas with rhabdoid features, nine of which originated in the pleura and one in the peritoneum. Eight of the patients were men and two were women. Six patients had a history of asbestos exposure. Histologically, seven of the mesotheliomas were epithelioid, two sarcomatoid, and one biphasic. The proportion of the rhabdoid cells seen in these cases constituted 15-75% of the individual tumors. Cytoplasmic staining in the rhabdoid cells was seen for pan-keratin and vimentin in all 10 cases, for keratin 7 in eight of eight, for calretinin in nine of 10, and for keratin 5/6 in seven of nine. Nuclear positivity for WT1 was observed in the rhabdoid cells of four of seven cases and membranous reactivity for mesothelin in four of six, and for podoplanin in two of six. Only one case showed desmin positivity in sparse cells in the nonrhabdoid component of the tumor. All of the cases were negative for CEA, MOC-31, TAG-72, CD15, CD34, bcl2, muscle-specific actin, and TTF-1. Ultrastructural studies revealed paranuclear collections of intermediate filaments, but no evidence of rhabdomyoblastic differentiation was seen. The mean survival of five of the six patients for whom this information was available was 3.8 months. The remaining patient had a survival time of 1 year. It is important for pathologists to be aware that mesotheliomas can present rhabdoid features, not only because they can be confused with other malignancies that can exhibit a similar morphology, but also because of their apparently unusually aggressive behavior. The value of immunohistochemistry and electron microscopy in the differential diagnosis of these tumors is discussed.

Differential diagnosis of benign and malignant mesothelial proliferations on pleural biopsies

CONTEXT

Although much of the pathology literature focuses on differential diagnosis of diffuse malignant mesothelioma from other types of cancer, the primary diagnostic challenge facing the pathologist is often whether a mesothelial proliferation on a pleural biopsy represents a malignancy or a benign reactive hyperplasia.

DESIGN

Based on previous medical publications, extensive personal consultations, and experience on the United States-Canadian Mesothelioma Reference Panel and the International Mesothelioma Panel, salient information was determined about interpretation of benign versus malignant mesothelial proliferations on pleural biopsies.

RESULTS

Differentiation of benign reactive mesothelial hyperplasia from diffuse malignant mesothelioma is often difficult. Benign reactive mesothelial hyperplasia may mimic many features ordinarily associated with malignancy, and diffuse malignant mesothelioma may be cytologically bland. Entrapment of benign reactive mesothelial cells within organizing pleuritis may mimic tissue invasion.

CONCLUSIONS

Various histologic clues favor a benign over a malignant mesothelial proliferation and vice versa. Invasion is the most reliable criterion for determining that a mesothelial proliferation is malignant. When there is any doubt that a pleural biopsy represents a malignancy, we recommend a diagnosis of atypical mesothelial proliferation.

Desmoplastic round cell tumor of childhood: can cytology with immunocytochemistry serve as an alternative for tissue diagnosis?

There are limited reports on the cytology of desmoplastic small round cell tumors (DSRCT). Fine needle aspiration biopsy (FNAB) findings in seven aspirates from four cases of histologically and immunohistochemically confirmed cases were analyzed with the main intention of ascertaining if cytological diagnosis of DSRCT is possible. Also assessed were the immunocytochemistry(ICC) findings in these cases. The basic cytological impression was that of a cohesive small round cell tumor. Nuclei showed granular chromatin with grooves, nuclear molding and inconspicuous nucleoli. Stromal fragments were noted in all four cases. In two cases, awareness of cytological features in the appropriate clinical context led to a suggestion of the diagnosis of DSRCT on cytology itself. ICC on destained smears showed positivity for cytokeratin, epithelial membrane antigen (EMA), desmin and WT-1 in two cases. In conclusion, given the right clinical setting, a cytological diagnosis of DSRCT is plausible and in conjunction with ICC may help in documenting the polyphenotypic nature and thereby confirming the diagnosis.

Caveolin-3 Is a Sensitive and Specific Marker for Rhabdomyosarcoma

Caveolin-3 (Cav-3) is a principal structural protein of caveolae membrane domains. Animal studies have revealed that Cav-3 is expressed in skeletal and cardiac myocytes but absent in other types of cells. Recent studies have shown that abnormalities in the Cav-3 gene are associated with some forms of muscular dystrophy, while skeletal muscle abnormalities have been observed in Cav-3 transgenic and knockout mice. In this study the authors evaluated the distribution of Cav-3 in normal human tissues and compared the expression of Cav-3 with that of myogenin and myoD1 in rhabdomyosarcoma (RMS), malignant mixed mullerian tumor (MMMT), and an array of neoplasms that mimic RMS to assess the utility of Cav-3 as a diagnostic marker for tumors with skeletal muscle differentiation. In nonneoplastic human tissues, crisp membrane staining for Cav-3 was present in cardiac and skeletal myocytes and occasionally in arterial smooth muscle cells and prostatic stromal cells, while other cell types were negative for Cav-3. Eighty-eight percent (21/24) of RMS studied were positive for Cav-3. Positive staining was generally observed in the more maturely differentiated tumor cells but not the primitive tumor cells. Eight of nine cases of MMMT stained strongly with Cav-3 in their rhabdomyosarcomatous component but not in other components. Fifty-four other neoplasms (13 leiomyosarcomas, 8 neuroblastomas, 5 lymphomas, 6 Wilms tumors without skeletal muscle differentiation, 5 Ewing sarcomas, 4 malignant fibrous histiocytomas, 4 angiosarcomas, 6 malignant melanomas, and 3 synovial sarcomas) were negative for Cav-3 expression. Nearly all (96% [23/24]) cases of RMS were positive for myogenin, while 88% (21/24) were positive for myoD1. Primitive tumor cells showed significantly increased expression of myoD1 and myogenin; conversely, more differentiated tumor cells were negative or weakly stained. The rhabdomyosarcomatous component of MMMT stained focally with myogenin and myoD1, in contrast to the strong Cav-3 labeling in these cells. These results demonstrate that Cav-3 is specifically expressed in human cardiac and skeletal myocytes. Furthermore, its high specificity and relatively high sensitivity (88%) for tumors with skeletal muscle differentiation suggest that Cav-3 is a valuable marker for these tumors and may be used to assess the degree of differentiation of RMS and to identify residual tumor cells in post-chemotherapy specimens.

Immunohistochemical analysis of a muscle ankyrin-repeat protein, Arpp, in paraffin-embedded tumors: evaluation of Arpp as a tumor marker for rhabdomyosarcoma

Arpp, a protein including an ankyrin-repeat, P EST motif, and p roline-rich region, is a recently identified protein that is exclusively expressed in striated muscles. This study comprehensively analyzed its expression among soft tissue sarcomas of various histological types and evaluated its potential use for the differential diagnosis of rhabdomyosarcoma (RMS). Formalin-fixed, paraffin-embedded tissues, including 37 RMS cases, 88 non-RMS sarcomas, and 38 carcinomas, were analyzed for Arpp expression. Arpp was detected in 33 (89.2%) of 37 RMS cases by immunohistochemistry. Western blot analysis revealed expression of Arpp in all RMS cases tested. High expression of Arpp was generally associated with morphological evidence of skeletal muscle differentiation of tumor cells. In contrast, Arpp displayed 6.3% (8/126) positivity among the non-RMS tumors. Focal or weak expression was seen in malignant fibrous histiocytoma (2/27), synovial sarcoma (1/11), Ewing sarcoma (1/5), and epithelioid sarcoma (3/5), whereas one epithelioid sarcoma displayed strong expression for Arpp. A comparative analysis of the Arpp profile with that of myogenic markers in RMS revealed that the sensitivity of Arpp (89.2%) was higher than that of myoglobin (59.6%) and comparable with that of myogenin (88.2%), MyoD (80.6%), muscle-specific actin (83.8%), and desmin (89.2%). These results suggested that Arpp is sensitive to and specific for RMS. Thus, we proposed that Arpp is a novel skeletal muscle-specific marker, which is useful for differential diagnosis of RMS.

Pathology of mesothelioma

In this article, progress in distinguishing mesothelioma from mesothelial hyperplasia and fibrosing pleuritis was discussed. Advances in the immunohistochemical characterization of mesothelioma, in the recognition of entities that mimic mesothelioma, and in their distinction from mesothelioma were reviewed. Cytogenetic and molecular genetic contributions to the diagnosis of pleural synovial sarcoma were briefly summarized. The diagnosis of epithelial type mesothelioma can be established in most cases. Several mesotheliomas, however, especially rare subtypes, and sarcomatoid, desmoplastic, and poorly differentiated mesotheliomas continue to present diagnostic challenges.

Mesothelial progenitor cells and their potential in tissue engineering

The mesothelium consists of a single layer of flattened mesothelial cells that lines serosal cavities and the majority of internal organs, playing important roles in maintaining normal serosal integrity and function. A mesothelial 'stem' cell has not been identified, but evidence from numerous studies suggests that a progenitor mesothelial cell exists. Although mesothelial cells are of a mesodermal origin, they express characteristics of both epithelial and mesenchymal phenotypes. In addition, following injury, new mesothelium regenerates via centripetal ingrowth of cells from the wound edge and from a free-floating population of cells present in the serosal fluid, the origin of which is currently unknown. Recent findings have shown that mesothelial cells can undergo an epithelial to mesenchymal transition, and transform into myofibroblasts and possibly smooth muscle cells, suggesting plasticity in nature. Further evidence for a mesothelial progenitor comes from tissue engineering applications where mesothelial cells seeded onto tubular constructs have been used to generate vascular replacements and grafts to bridge transected nerve fibres. These findings suggest that mesothelial cell progenitors are able to switch between different cell phenotypes depending on the local environment. However, only by performing detailed investigations involving selective cell isolation, clonal analysis together with cell labelling and tracking studies, will we begin to determine the true existence of a mesothelial stem cell.

The use of immunohistochemistry in distinguishing reactive from neoplastic mesothelium. A novel use for desmin and comparative evaluation with epithelial membrane antigen, p53, platelet-derived growth factor-receptor, P-glycoprotein and Bcl-2

AIMS

To evaluate the expression of the intermediate filament desmin in reactive mesothelium and malignant mesothelioma and to compare its utility with five other previously reported immunomarkers claimed to be of use in distinguishing reactive from neoplastic mesothelium.

METHODS AND RESULTS

Sixty cases of malignant pleural mesothelioma and 40 cases of reactive mesothelial hyperplasia formed the study group. Cases were immunohistochemically stained with desmin, epithelial membrane antigen (EMA), p53, Bcl-2, P-glycoprotein and platelet-derived growth factor receptor (PDGF-R) beta-chain by the avidin-biotin complex method. The cohort of malignant pleural mesotheliomas were immunoreactive to desmin, EMA and p53 in 6/60 (10%), 48/60 (80%) and 27/60 (45%), respectively. In comparison, the cohort of reactive mesothelial hyperplasias were immunoreactive to desmin, EMA and p53 in 34/40 (85%), 8/40 (20%) and 0/40 (0%), respectively. In a smaller cohort (n = 15) of malignant pleural mesotheliomas, Bcl-2, P-glycoprotein and PDGF-R beta-chain were expressed in 0/15 (0%), 2/15 (13%) and 15/15 (100%), respectively. In a small cohort (n = 15) of reactive mesothelial hyperplasias, Bcl-2, P-glycoprotein and PDGF-R beta-chain were immunoreactive in 0/15 (0%), 0/15 (0%) and 6/15 (40%), respectively.

CONCLUSIONS

Desmin and EMA appear to be the most useful markers in distinguishing benign from malignant mesothelial proliferations. Desmin appears to be preferentially expressed in reactive mesothelium and EMA appears to be preferentially expressed in neoplastic mesothelium. The complementary use of both markers is advocated in ascertaining the nature of mesothelial proliferations. Immunohistochemical detection of mutated p53 oncoprotein appeared to be of less utility in this study on account of the low marker sensitivity for malignant mesothelioma. However, p53 antibody may be of use as a second-line marker of neoplastic mesothelium within a standard immunohistochemical panel of antibodies. In this study, Bcl-2, P-glycoprotein and PDGF-R beta-chain appear to be of no use in distinguishing reactive from neoplastic mesothelium, although more formal evaluation of these markers is required.

Diagnostic use of muscle markers in the cytologic evaluation of serous fluids

Differentiating reactive mesothelial cells from malignant mesotheliomas and from adenocarcinomas can be diagnostically challenging when based solely on the morphologic examination of serous fluids. The diagnosis even after the use of standard immunohistochemical stains may at times be inconclusive because of the variable reactivity of mesothelial cells for these markers. Pathologists and cytologists underutilize reactivity for desmin, a feature of mesothelial cells apparently not shared by adenocarcinomas. The purpose of this study was to evaluate the extent to which mesothelial cells express muscle differentiation and to assess the diagnostic utility of muscle markers in distinguishing reactive mesothelial cells from malignant mesotheliomas and adenocarcinomas. Archival paraffin-embedded cell blocks of serous fluids from 24 cases of reactive mesothelial cells, 14 cases of malignant mesothelioma, and 56 cases (14 cases from each) of metastatic adenocarcinoma from the lung, breast, ovary, and gastrointestinal tract were retrieved. Five cases of omentum with unremarkable mesothelial cells were also included in the study. All cases were stained for desmin, actin, myoglobin, and myogenin and evaluated independently by two observers. Strong cytoplasmic reactivity for desmin was noted in 22 of 24 cases (92%) of reactive mesothelial cells. The reactive mesothelial cells did not express actin, myoglobin, or myogenin. All cases of malignant mesothelioma and metastatic adenocarcinoma were negative for the four muscle markers. The mesothelial lining and scattered subserosal cells in the omental sections were positive for desmin. Because desmin was expressed only in benign mesothelial cells, it may serve as a reliable marker in distinguishing reactive mesothelial cells from mesothelioma or from adenocarcinoma. Awareness of this staining pattern is also important to avoid pitfalls when evaluating body fluid specimens from patients with a history of tumors expressing muscle differentiation.

Cytology of desmoplastic small round cell tumor

BACKGROUND

Desmoplastic small round cell tumor (DSRCT) is a high-grade malignant tumor that has a predilection for adolescent males and usually affects the abdominal cavity. The cytology literature regarding DSRCT, including aspirates and ascitic fluid, is limited. To the authors' knowledge, findings in ThinPrep slides have not been described previously.

METHODS

Seven cytologic specimens from five patients with histologically confirmed DSRCT were reviewed. Five specimens were fine-needle aspiration biopsies (FNABs), (liver, flank soft tissue, abdomen, and two resected colons [pericolic]) and two specimens were ascitic fluid. Cytologic features were studied in ThinPrep slides and direct smears, which included hematoxylin and eosin, Papanicolaou, and Quik-Dip stains.

RESULTS

All specimens showed moderate to high cellularity. The tumor cells were arranged singly and in clusters. The cells demonstrated high nuclear/cytoplasmic ratios, granular chromatin reminiscent of small cell carcinoma, usually inconspicuous nucleoli, smooth to irregular nuclear membranes, and frequent nuclear molding. The cytoplasm was scant to moderate, pale blue, and occasionally vacuolated. Pseudorosettes were observed in six specimens. One ThinPrep slide and the direct smears contained cells with perinuclear, cytoplasmic densities. Stromal fragments were present in the direct smears but were uncommon in ThinPrep. Three specimens were diagnosed as being consistent with DSRCT. Two specimens were diagnosed as malignant small cell tumor. Molecular studies performed on histologic material in four cases confirmed the presence of the diagnostic translocation, t(11;22)(p13;q12).

CONCLUSIONS

DSRCT may be diagnosed accurately in cytology specimens. Characteristic cytologic features include granular chromatin, smooth to irregular nuclear membranes, nuclear molding, cytoplasmic vacuoles, pseudorosettes, and metachromatic stroma. Cytoplasmic densities may be observed in direct smears and ThinPrep slides.

The role of desmin and N-cadherin in effusion cytology: a comparative study using established markers of mesothelial and epithelial cells

The objective of the present study was to analyze the role of the mesothelial markers desmin and N-cadherin in the diagnostic panel of serous effusions. A total of 181 pleural and peritoneal effusions consisted of 101 cases cytologically diagnosed as malignant (89 carcinomas, 12 mesotheliomas), 78 benign, and 2 inconclusive specimens. All specimens were immunostained using 11 antibodies, against epithelial membrane antigen, Ber-EP4, carcinoembryonic antigen, E-cadherin, CA 125, N-cadherin, desmin, calretinin, p53, vimentin, and CD45. After evaluation of immunocytochemistry results, 110 specimens were diagnosed as malignant (98 carcinomas, 12 mesotheliomas) and 71 as benign (56 cellular, 15 paucicellular). The presence of desmin was detected in benign mesothelial cells in 47 of 56 (84%) reactive cellular specimens compared with 1 of 12 (8%) malignant mesotheliomas and 2 of 98 (2%) carcinomas. N-cadherin was expressed in 48 of 56 (86%) reactive cases, 12 of 12 (100%) mesotheliomas, and 47 of 98 (48%) carcinomas. In carcinomas, N-cadherin expression was most often seen in ovarian carcinoma but was also found in other carcinomas. Calretinin, an established marker of mesothelial cells, was detected in 52 of 56 (93%) reactive specimens, 11 of 12 (93%) mesotheliomas, and 3 of 98 (3%) carcinomas. Evaluation of staining results led to reclassification of six malignant specimens as benign, whereas 17 cases diagnosed as benign and the two diagnosed as inconclusive were classified as malignant. In conclusion, desmin appears to be a promising marker for the distinction between reactive mesothelium and malignant epithelial cells in terms of both specificity and sensitivity, and its complementary use with calretinin is recommended. Unlike calretinin, it may also prove valuable for the distinction between benign and malignant mesothelial cells. N-cadherin does not have a role in the distinction between mesothelial and epithelial cells. However, it may prove useful in the characterization of carcinomas of unknown origin. As has previously been shown, a significant number of diagnoses that are based on morphologic examination alone are modified after the use of a broad antibody panel.

Leiomyosarcoma of the paratesticular region: a clinicopathologic study

The behavior of leiomyosarcoma (LMS) is site related, but there are limited data on such tumors presenting in the paratesticular region. Cases diagnosed as LMS of the paratesticular region from the files of three institutions were reviewed. Immunohistochemistry was performed in cases with available blocks, and follow-up information was obtained. From 31 cases originally diagnosed as LMS, 24 were retained after review. These were from men aged 34-86 years (mean 62 years; median 64 years) and involved the testicular tunica (10), spermatic cord (10), scrotal subcutis and dartos muscles (1 each), and the epididymis (1). Tumors ranged in size from 2-9 cm (mean 5 cm; median 4 cm). On immunohistochemical staining they expressed muscle-specific actin (13 of 14), smooth muscle actin (10 of 10), desmin (16 of 17), and CD34 (3 of 9); all of the latter three were strongly desmin-positive. Focal reactivity for cytokeratin (3 of 8) and S-100 protein (1 of 8) was seen. Follow-up information was available in 14 patients. Four (29%) had recurrences, in one case four times. Metastases to lymph nodes, lungs, or liver were seen in four patients (29%), of whom two had prior recurrences. Ten were alive with no evidence of disease (ANED), and four were dead of disease (DOD). Comparing outcome with tumor grade, all seven patients with grade 1 tumors (of whom two had recurrences) and all three with grade 2 tumors were ANED, whereas all four patients with grade 3 tumors were DOD. In summary, paratesticular LMSs are rare neoplasms. The majority in this site are low-grade, although high-grade lesions behave aggressively.

Primary Mesenteric Malignant Mixed Mesodermal (Müllerian) Tumor with Neuroendocrine Differentiation

Extragenital malignant mixed mesodermal (müllerian) tumors (MMMT) are rare neoplasms, with but 24 well documented cases in the literature. Neuroendocrine differentiation in mixed müllerian neoplasms has been mentioned only anecdotally. We report on the clinical, pathological, and immunohistochemical features of a hitherto-undescribed extragenital MMMT with prominent neuroendocrine differentiation arising from the jejunal mesentery. This lesion was composed of a poorly differentiated epithelial component and a spindle cell component with heterologous (rhabdomyoblastic) differentiation. The bulk of the tumor consisted of small cell neuroendocrine carcinoma, which exhibited strong immunoreactivity for NSE, LEU-7, chromogranin A and synaptophysin. Electronmicroscopy confirmed the presence of neurosecretory dense-core granules. The primary mesenteric origin of the tumor was established at autopsy. Along with a brief review of previously reported extragenital MMMT some histogenetic concepts relevant to this case are discussed.

Paranemin and the organization of desmin filament networks

De novo expression of vimentin, GFAP or peripherin leads to the assembly of an extended intermediate filament network in intermediate filament-free SW13/cl.2 cells. Desmin, in contrast, does not form extended filament networks in either SW13/cl.2 or intermediate filament-free mouse fibroblasts. Rather, desmin formed short thickened filamentous structures and prominent spot-like cytoplasmic aggregates that were composed of densely packed 9–11 nm diameter filaments. Analysis of stably transfected cell lines indicates that the inability of desmin to form extended networks is not due to a difference in the level of transgene expression. Nestin, paranemin and synemin are large intermediate filament proteins that coassemble with desmin in muscle cells. Although each of these large intermediate filament proteins colocalized with desmin when coexpressed in SW-13 cells, expression of paranemin, but not synemin or nestin, led to the formation of an extended desmin network. A similar rescue of desmin network organization was observed when desmin was coexpressed with vimentin, which coassembles with desmin, or with keratins, which formed a distinct filament network. These studies demonstrate that desmin filaments differ in their organizational properties from the other vimentin-like intermediate filament proteins and appear to depend upon coassembly with paranemin, at least when they are expressed in non-muscle cells, in order to form an extended filament network.

Anti-mesothelial markers in sarcomatoid mesothelioma and other spindle cell neoplasms

AIMS

To undertake a comparative evaluation of three antimesothelial markers (thrombomodulin, cytokeratin 5/6 and calretinin) with broad spectrum cytokeratin (AE1/AE3) in differentiating between sarcomatoid mesothelioma and a spectrum of spindle cell neoplasms.

METHODS AND RESULTS

Thirty-one malignant sarcomatoid mesotheliomas were studied. Calretinin expression was focally identified in 12 (39%) tumours and thrombomodulin and cytokeratin 5/6 immunoreactivity was seen in nine (29%) cases. In comparison there was strong diffuse cytoplasmic reactivity with the broad spectrum cytokeratin (AE1/AE3) in 24 of 31 (77%) tumours. Thirty mixed spindle cells neoplasms were studied. No calretinin expression was identified in any case. Thrombomodulin immunoreactivity was identified in four (16%) cases (two angiosarcomas, two high-grade sarcomas, not otherwise specified). Cytokeratin 5/6 expression was seen in one high-grade pulmonary sarcoma originally termed malignant fibrous histiocytoma. None of the antimesothelial markers was expressed in the four spindle cell carcinomas studied. In contrast, broad spectrum cytokeratin was diffusely expressed in all four spindle cell carcinomas (three pulmonary, one renal), both synovial sarcomas, both malignant mixed Müllerian tumours, one of three pulmonary leiomyosarcomas and two of nine sarcomas, not otherwise specified.

CONCLUSIONS

Immunohistochemistry has a more limited role in the diagnosis and distinction of sarcomatoid mesothelioma from other spindle cell neoplasms. The combination of a broad spectrum cytokeratin with calretinin combines both high sensitivity (77% for AE1/AE3) with high specificity (100% for calretinin) for sarcomatoid mesothelioma and can be diagnostically useful. The mesothelial markers, thrombomodulin and cytokeratin 5/6, are not useful alone in the diagnosis of sarcomatoid mesothelioma as each shows insufficient antibody sensitivity, although together they complement calretinin.

Image analysis and flow cytometric DNA studies of benign and malignant body cavity fluids: reappraisal of the role of current methods in the differential diagnosis of reactive versus malignant conditions

Cytologic examination of body fluids is commonly performed in the clinical laboratory. Determination of the presence of malignancy may sometimes be difficult. In this study, we prospectively studied 60 body fluids with a panel of antibodies, including MOC-31, epithelial membrane antigen, carcinoembryonic antigen, B72.3, keratin, desmin, and CA-125. DNA and S-phase studies were performed both by flow cytometry and image analysis. Thirty-seven fluids were classified as benign and 23 were classified as malignant. The sensitivity of the antibodies for identification of carcinoma in descending order of percentage detection rate were MOC-31 (95%), epithelial membrane antigen (93%), B72.3 (84%), and carcinoembryonic antigen (80%). Desmin stained mesothelial cells in all cases. CA-125 gave similar results but was less specific. Flow cytometry detected 14 of 20 malignant fluids and image analysis 17 of 23 by identifying an aneuploid population. Benign reactive mesothelial cells were not aneuploid. Tetraploidy due to reactive mesothelial cells was found in 9 of 37 body fluids. Their S-phase fraction was low (average, 3.2%). Tetraploidy in malignant cells was distinguished from the reactive mesothelial cells by high S-phase (average, 25.95). S-phase had some use as a discriminating factor, because no benign reactive cases had more than 17%. However, 7 of 23 malignant cases had a value below 17%. DNA analysis by image was more sensitive and specific than flow. Either may be used when immunocytochemistry is nondiagnostic or cannot be performed.

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.

NCAM (neural cell adhesion molecules) expression in malignant mesotheliomas

Neural cell adhesion molecules (NCAM) are adhesion molecules expressed by neural and neuroendocrine tumors and a few biphasic tumors such as synovialosarcomas and breast phyllode tumors. To investigate NCAM expression in mesotheliomas, we studied 26 cases of epithelioid (n = 12), biphasic (n = 11), and sarcomatoid (n = 3) malignant mesotheliomas (MM), in comparison with normal mesothelium, and 50 primary non-small cell lung carcinomas (NSCLC) (25 adenocarcinomas [ADC] and 25 squamous cell carcinomas [SCC]), using electron microscopy as a gold standard for recognition of MM. NCAM reactivity using 123C3 antibody was compared with that of NE markers such as chromogranin A and synaptophysin. Although normal mesothelium remains negative, NCAM was expressed in 19 of 26 MM (73%) with a membranous staining on frozen or paraffin sections. In 6 of 12 epithelioid MM, the tumor cells expressed NCAM, whereas in 5 cases stromal fibroblasts showed a strong but focal staining. In 11 biphasic MM, 4 presented an NCAM reactivity of both epithelioid and spindle cell components, whereas in 7, only fusiform component was NCAM positive. Two of 3 sarcomatoid MM showed an NCAM expression. Chromogranin expression was never seen, whereas synaptophysin was noticed in 2 cases. No case of NSCLC showed membranous 123C3 staining, whereas 2 ADC weakly expressed synaptophysin. We conclude that NCAM expression in MM is reminiscent of its expression in mesoderm during fetal life and consistent with that reported in other biphasic tumors. These data show that NCAM expression occurs in 73% of MM, highly exceeding that observed in lung cancer.

Desmoplastic small round cell tumor: II: an ultrastructural and immunohistochemical study with emphasis on new immunohistochemical markers

In order to investigate the histogenesis and facilitate the diagnosis of desmoplastic small round cell tumor (DSRCT), 39 cases were studied by immunohistochemical methods using a large battery of antibodies directed against a wide variety of epithelial, mesenchymal, and neural-associated proteins. Sixteen of these tumors were also studied by electron microscopy. Thirty-seven of 39 cases reacted for cytokeratin using a "cocktail" of 3 monoclonal antibodies (CAM 5.2/AE1/AE3), 39/39 for desmin, 24/25 for epithelial membrane antigen, 22/27 for vimentin, 18/25 for neuron-specific enolase, 10/15 for CD57 (Leu-7), 3/19 for synaptophysin, 1/22 for chromogranin, 3/19 for muscle-specific actin, 3/16 for alpha-smooth-muscle actin, 11/16 for CD15 (Leu-M1), 5/12 for CA-125, 6/17 for CD99, 9/10 for MOC-31, 2/6 for NB84, 5/7 for Ber-EP4, and 8/9 for the Wilms tumor (WT1) protein. No staining was obtained in any of the cases tested for cytokeratin 5/6 or 20, neurofilament proteins, glial fibrillary acidic protein, peripherin, CA19-9, thrombomodulin, alphafetoprotein, carcinoembryonic antigen, TAG-72 (B72.3), placental alkaline phosphatase, S-100 protein, HMB-45, myoglobin, or for the two myogenic regulatory proteins myogenin and MyoD1. A frequent ultrastructural finding was the presence of juxtanuclear aggregates of intermediate filaments, but microfilaments with densities or Z-band-like material suggestive of either smooth or skeletal muscle differentiation were not seen in any case. Dendritic-like processes containing microtubules and dense core granules were seen in four tumors and all of these tumors reacted for at least one of the neural markers investigated. Although ultrastructural and immunohistochemical studies confirmed previous observations that DSRCTs present epithelial, mesenchymal, and neural phenotypes, a great variation was found in the frequency of expression of the different markers used to demonstrate each line of cell differentiation. The absence of expression of cytokeratin 5/6 and thrombomodulin together with positive staining for CD15, MOC-31, and Ber-EP4 argues against the possible mesothelial origin that has been suggested for this tumor. Additionally since none of the tumors reacted for myogenin or MyoD1, desmin expression in DSRCT cannot be regarded as evidence of skeletal muscle differentiation. Although the histogenesis of DSRCT remains unknown, it is believed that this tumor originates from a progenitor cell with potential for multiphenotypic differentiation.

Alveolar soft-part sarcoma: a review of the pathology and histogenesis

The descriptive designation, alveolar soft-part sarcoma, continues to be used for this uncommon soft-tissue malignancy because an acceptable hypothesis for its histogenesis has not been advanced, despite studies with electron microscopy and immunohistochemistry. These techniques have, nevertheless, provided significant information that is useful in the differential diagnosis of the tumor and pertinent in speculation concerning its nature. The most intriguing ultrastructural feature is the secretory process that culminates in the formation of the distinctive cytoplasmic crystals. Myogenic differentiation has been favored in a number of recent reports on the basis of immunohistochemical findings and the presence of the crystals does not rule out the possibility, but accounts of immunoreactivity for the myogenic regulatory protein MyoD1 have not been confirmed in subsequent studies or in the authors' own staining of six cases.

A comparative evaluation of immunohistochemical markers for the differential diagnosis of malignant pleural tumours

AIMS

To determine the value of immunocytochemistry in differentiation of malignant pleural mesothelioma from carcinoma in a pleural biopsy using commercially available monoclonal antibodies.

METHODS AND RESULTS

A panel of monoclonal antibodies against keratins, epithelial membrane antigen (EMA), epithelial antigen Ber-EP4, carcinoembryonic antigen (CEA), tumour-associated glycoprotein (B72.3), Leu-M1, CD30 (Ber-H2), vimentin and desmin, was applied to 40 cases of malignant pleural mesothelioma and 23 cases of carcinoma metastatic to the pleura (16 pulmonary and seven extrapulmonary). Positivities for Ber-EP4, CEA, B72.3 and Leu-M1 were found to have the highest nosologic sensitivities (87.0%, 65.2%, 52.5% and 43.5%, respectively) and specificities (97.5%, 97.5%, 100% and 95%, respectively) for carcinoma. Positive staining for vimentin had the highest sensitivity (87.5%) with 95.7% specificity for mesothelioma. Positive staining for desmin was found in 45% of mesotheliomas and 0% of carcinomas. Diagnostic sensitivity and diagnostic specificity (P-values) were calculated for these markers. In respect to the diagnostic power defined by the clinically relevant predictive values of positive and negative tests, we found that a two-marker panel of antibodies including vimentin and Ber-EP4 is most useful for the histopathological distinction between carcinoma (pulmonary or extrapulmonary) and malignant pleural mesothelioma.

CONCLUSIONS

A combination of Ber-EP4 and vimentin provides the most sensitive and specific pair of markers for distinguishing between malignant pleural mesothelioma and carcinoma metastatic to the pleura. The prevalence of the tested tumours should be taken into account when evaluating the clinical value of ancillary techniques in pathology.

Immunohistochemical evidence of the mesothelial histogenesis of a uterine adenomatoid tumor

We present rare case of a uterine adenomatoid tumor. In order to characterize the diversity of immunoreactive antigens associated with mesothelial differentiation, we immunohistochemically examined the tumor's epithelioid and myofibromatoid components, as well as the biphasic pattern of its adenomatoid changes. Immunostaining of tumor cells was positive for high- and low-molecular-weight cytokeratins and vimentin. Specific immunoreactions with antibodies against desmin, alpha-actin, and the S-100 protein also were observed. The present adenomatoid tumor can be explained in terms of various transformations and typical alterations in mesothelioma cells: (1) the mesothelial cells had differentiated to epithelial and stromal components, concomitant with the presence of predominant reactive foci; (2) intermediate cells expressed different types of cytoskeletal intermediate filament proteins (IMPs); and (3) the patterns of fibromatoid and leiomyoid differentiation resembled those of a benign mesothelioma of the ovarian or oviductal peritoneum. Our immunohistochemical investigations indicated that the present tumor exhibited the histogenesis of a true mesothelioma, an adenomatoid mesothelioma.