Podoplanin (d2-40): a new immunohistochemical marker for reactive follicular dendritic cells and follicular dendritic cell sarcomas

The diagnosis of follicular dendritic cell (FDC) sarcoma can be challenging because of its morphologic overlaps with many other spindle cell neoplasms and, therefore, new phenotypic markers will be helpful in its differential diagnosis. Podoplanin is a mucin-type transmembrane glycoprotein that has recently been detected in reactive FDCs. In this study, we investigated the expression patterns of podoplanin using a new mouse monoclonal antibody D2-40, and compared them with CD21, a well-established FDC marker, in a comprehensive panel of cases. The panel included 4 FDC sarcomas, 38 spindle cell neoplasms of other types, 25 reactive lymphoid hyperplasia, and 117 lymphoid and 5 myeloid malignant hematopoietic neoplasms. Our study revealed that D2-40 strongly stained 3 of 4 FDC sarcomas. In contrast, D2-40 stained only 2/38 other spindle cell neoplasms tested. Furthermore, we observed that D2-40 highlighted more FDC meshworks than CD21 in Castleman's disease, follicular lymphoma, nodular lymphocyte predominance Hodgkin lymphoma, and residual reactive germinal centers in a variety of lymphoma types. D2-40 and CD21 stained an equal number of cases of reactive lymphoid hyperplasia, progressively transformed germinal centers and angioimmunoblastic T-cell lymphoma. No expression of podoplanin was detected in normal or neoplastic lymphoid and myeloid cells. We conclude that podoplanin (D2-40) is a sensitive and specific FDC marker, which is superior or equal to CD21 in evaluating both reactive and neoplastic FDCs. In addition, our results suggest that podoplanin (D2-40) can be used to support the diagnosis of FDC sarcoma.     

Expression of podoplanin in human bone and bone tumors: New marker of osteogenic and chondrogenic bone tumors

Podoplanin is known as a lymphatic marker because its expression is detected in lymphatic but not vascular endothelium. Podoplanin is also expressed in several normal tissues including osteocytes or osteoblasts. A systematic examination of the podoplanin expression was conducted in normal skeletal tissues and some bone tumor cell lines, and the diagnostic value determined in primary bone tumors. Podoplanin mRNA was expressed at a high level in bone marrow tissue and cartilage, and was upregulated with differentiation to osteoblasts in bone marrow cells. Strong podoplanin expression was seen in osteocytes, chondrocytes, and osteoblasts on immunohistochemistry. Podoplanin mRNA was expressed at a high level in several osteosarcoma and chondrosarcoma cell lines, whereas podoplanin was expressed at a low level in a Ewing's/primitive neuroectodermal tumor cell line. In the clinical samples, osteosarcomas (22/26) expressed podoplanin at various levels. In small cell osteosarcomas (2/2), podoplanin was expressed strongly, although the tissue samples included few diagnostic osteoids. Chondrosarcomas (10/10) expressed podoplanin strongly, and chondroblastomas (5/5) expressed podoplanin moderately, while podoplanin was absent or expressed at low levels in Ewing's sarcomas (0/5), chordomas (0/6) and giant cell tumors of bone (1/7). Therefore, podoplanin may be a sensitive immunohistochemical marker of osteogenic and chondrogenic bone tumors.     

Diagnostic implications of podoplanin expression in peripheral nerve sheath neoplasms

By using the D2-40 antibody, we have observed podoplanin expression in Schwann cells and perineurial cells. Podoplanin expression has not been well characterized in peripheral nerve sheath tumors. Because neoplasms of neural crest lineage, including peripheral nerve sheath and melanocytic neoplasms, may share histologic and immunohistochemical characteristics, we evaluated podoplanin and S-100 expression in these lesions to determine the usefulness of podoplanin as a diagnostic marker. Diffuse podoplanin and S-100 expression was observed in 16 (76%) of 21 classical schwannomas, 6 (100%) of 6 cellular schwannomas, and 3 (75%) of 4 epithelioid malignant peripheral nerve sheath tumors (EMPNSTs). Podoplanin was expressed in 3 (7%) of 43 neurofibromas, 16 (21%) of 75 spindle cell MPNSTs (SMPNSTs), and 1 (10%) of 10 spindle cell melanomas but was absent in conventional melanoma. Only rare neurofibromas and SMPNSTs showed strong coexpression of podoplanin and S-100. These results suggest diffuse podoplanin expression or coexpression of podoplanin and S-100 is limited to schwannoma and EMPNST and may be useful in the evaluation of these neoplasms.     

Podoplanin: a novel diagnostic immunohistochemical marker

Podoplanin is a transmembrane mucoprotein recognized by the recently commercially available D2-40 monoclonal antibody. Recent investigations have shown that podoplanin is selectively expressed in lymphatic endothelium as well as lymphangiomas, Kaposi sarcomas, and in a subset of angiosarcomas with probable lymphatic differentiation. Podoplanin has also been shown to be strongly expressed in seminomas, epithelioid mesotheliomas, and hemangioblastomas, and immunostaining for this marker can assist in the diagnosis of these tumors. This article reviews the current information on the applications of podoplanin immunostaining in surgical pathology.     

Angiosarcomas express mixed endothelial phenotypes of blood and lymphatic capillaries: podoplanin as a specific marker for lymphatic endothelium

Angiosarcomas apparently derive from blood vessel endothelial cells; however, occasionally their histological features suggest mixed origin from blood and lymphatic endothelia. In the absence of specific positive markers for lymphatic endothelia the precise distinction between these components has not been possible. Here we provide evidence by light and electron microscopic immunohistochemistry that podoplanin, a approximately 38-kd membrane glycoprotein of podocytes, is specifically expressed in the endothelium of lymphatic capillaries, but not in the blood vasculature. In normal skin and kidney, podoplanin colocalized with vascular endothelial growth factor receptor-3, the only other lymphatic marker presently available. Complementary immunostaining of blood vessels was obtained with established endothelial markers (CD31, CD34, factor VIII-related antigen, and Ulex europaeus I lectin) as well as podocalyxin, another podocytic protein that is also localized in endothelia of blood vessels. Podoplanin specifically immunolabeled endothelia of benign tumorous lesions of undisputed lymphatic origin (lymphangiomas, hygromas) and was detected there as a 38-kd protein by immunoblotting. As paradigms of malignant vascular tumors, poorly differentiated (G3) common angiosarcomas (n = 8), epitheloid angiosarcomas (n = 3), and intestinal Kaposi's sarcomas (n = 5) were examined for their podoplanin content in relation to conventional endothelial markers. The relative number of tumor cells expressing podoplanin was estimated and, although the number of cases in this preliminary study was limited to 16, an apparent spectrum of podoplanin expression emerged that can be divided into a low-expression group in which 0-10% of tumor cells contained podoplanin, a moderate-expression group with 30-60% and a high-expression group with 70-100%. Ten of eleven angiosarcomas and all Kaposi's sarcomas showed mixed expression of both lymphatic and blood vascular endothelial phenotypes. By double labeling, most podoplanin-positive tumor cells coexpressed endothelial markers of blood vessels, whereas few tumor cells were positive for individual markers only. From these results we conclude that (1) podoplanin is a selective marker of lymphatic endothelium; (2) G3 angiosarcomas display a quantitative spectrum of podoplanin-expressing tumor cells; (3) in most angiosarcomas, a varying subset of tumor cells coexpresses podoplanin and endothelial markers of blood vessels; and (4) all endothelial cells of Kaposi's sarcomas expressed the lymphatic marker podoplanin.     

Follicular dendritic cell sarcoma presenting as a submucosal tumor of the stomach

Follicular dendritic cell (FDC) sarcomas, especially those of extranodal origin, are extremely rare, and this entity could easily be missed without a high index of suspicion. We report a case of FDC sarcoma presenting as a submucosal tumor of the stomach in a 45-year-old man. The mass was a spindle and epithelioid mesenchymal tumor with many individually scattered and perivascular aggregates of lymphocytes. Immunohistochemical and ultrastructural studies confirmed the diagnosis. Although more than 50 cases of this tumor have been documented in the English literature, to our knowledge the presentation of FDC sarcoma as a submucosal tumor of the stomach has never been recorded. This case highlights the occurrence of FDC sarcoma as a submucosal tumor of the gastrointestinal tract. We believe that FDC sarcoma should be included in the differential diagnosis of spindle or epithelioid cell tumors of the gastrointestinal hollow viscus to prevent this still under-recognized tumor from being overlooked.     

Podoplanin as a marker for mesothelioma

Podoplanin is a specific marker for lymph vessel endothelial cells. It was noted that podoplanin is expressed in reactive mesothelial cells. The utility of podoplanin for the histological diagnosis of tumors was then investigated, especially for mesothelioma. Immunohistochemical study of podoplanin was carried out in five malignant mesotheliomas and 118 other tumors including 93 adenocarcinomas, four squamous cell carcinomas, six gastrointestinal stromal tumors and five endocrine tumors. Immunoreactivity for podoplanin was demonstrated on the cell membrane of tumor cells for all mesotheliomas. All other tumors were negative for podoplanin. Among the many antibodies used for differential diagnosis of malignant mesothelioma, podoplanin has the potential to be an excellent tumor marker in both specificity and sensitivity. The utility of podoplanin as a marker for mesothelioma will be confirmed by further studies.     

Podoplanin expression profiles characteristic of odontogenic tumor-specific tissue architectures

Podoplanin, a representative immunohistochemical marker for lymphatic endothelial cells, is also expressed in many other kinds of cancer cells, although its pathophysiological function is largely unknown. Our aim was to determine immunolocalization modes of podoplanin among odontogenic tumors to discuss possible roles of podoplanin in their characteristic tissue architecture formation. Immunohistochemical profiles of podoplanin were investigated in 40 surgical specimens from ameloblastoma (AM), adenomatoid odontogenic tumor (AOT), calcifying cystic odontogenic tumor (CCOT), and keratocystic odontogenic tumor (KCOT) in comparison with those of proliferating cell nuclear antigen (PCNA), integrin β1, fibronectin, and matrix metalloproteinase 9 (MMP-9). Podoplanin was localized in the basal cell layer or in the peripheral zone of AM foci. It was found in spindle-shaped tumor cells of AOT, in both the basal and polyhedral cells of CCOT, and in the basal and parabasal cells of KCOT linings. Podoplanin-positive (+) cells were located within areas of PCNA+ cells, and integrin β1 was localized in the cell membrane of podoplanin+ cells in the intercellular space where fibronectin and MMP-9 were deposited. In conclusion, podoplanin+ cells and areas in odontogenic tumors are in close associations with extracellular matrix signalings as well as cell proliferation.     

A survey of clusterin and fascin expression in sarcomas and spindle cell neoplasms: strong clusterin immunostaining is highly specific for follicular dendritic cell tumor.

Clusterin, a glycoprotein implicated in many cellular functions including apoptosis, has recently been shown to be strongly expressed in follicular dendritic cell tumors, and to be absent or only weakly expressed in other dendritic cell tumors. Fascin has also been investigated as a potential marker of dendritic cell neoplasms. We evaluated staining for antibodies directed against these two antigens in 202 spindle cell tumors, including cases of follicular dendritic cell tumor (n=14), interdigitating dendritic cell tumor (n=7), leiomyosarcoma (n=17), inflammatory myofibroblastic tumor (n=13), inflammatory pseudotumor (n=2), spindle cell thymoma (n=17), synovial sarcoma (n=11), fibrosarcoma (n=14), liposarcoma (n=27), gastrointestinal stromal tumor (n=13), malignant fibrous histiocytoma (n=18), angiomatoid fibrous histiocytoma (n=4), angiosarcoma (n=10), malignant peripheral nerve sheath tumor (n=8), malignant melanoma (n=16), and spindle cell carcinoma (n=11). Among these spindle cell neoplasms, strong diffuse clusterin staining had an overall specificity of 93% and a sensitivity of 100% for follicular dendritic cell tumor. Clusterin staining was least reliable in distinguishing follicular dendritic cell tumor from spindle cell thymoma or malignant fibrous histiocytoma, but these are entities that usually can be distinguished by clinical and morphologic data. Rare cases of leiomyosarcoma, fibrosarcoma and angiosarcoma may show strong clusterin staining. Fascin staining was very nonspecific among spindle cell tumors and thus does not imply a dendritic cell lineage.     

Cytopathology of a primary follicular dendritic cell sarcoma of the liver of the inflammatory pseudotumor-like type

Follicular dendritic cell (FDC) sarcoma is an exceedingly uncommon tumor of lymph nodes and extranodal tissues. The inflammatory pseudotumor (IPT)-like variant of FDC sarcoma of intraabdominal location is considered a separate entity, with different clinical and pathological features than those of the classic FDC tumor. There have been only 12 cytological reports of FDC sarcomas in the literature. Two of them were metastases to the liver and, like our case, had features of IPT. Fine-needle aspiration biopsy (FNAB) and imprint and scrape cytology from the surgically excised tumor here reported revealed spindle tumor cells with moderate pleomorphism, nuclear grooves, prominent nucleoli, and cytoplasmic processes, admixed with inflammatory cells. To the best of our knowledge, this is the first cytology report of a primary hepatic FDC tumor. The cytological findings permit the recognition of this tumor. However, confirmation by inmunohistochemistry (IHQ) is mandatory for a definitive diagnosis.     

NY-ESO-1 expression in synovial sarcoma and other mesenchymal tumors: significance for NY-ESO-1-based targeted therapy and differential diagnosis

A promising targeted therapy against NY-ESO-1 (CTAG 1B) using genetically modified T-cells in synovial sarcomas was recently demonstrated in a clinical trial at the NCI. To investigate the role of NY-ESO-1 immunohistochemistry in patient selection and gain better insight into the incidence of NY-ESO-1 expression in synovial sarcomas and other mesenchymal tumors, we evaluated NY-ESO-1 expression by immunohistochemistry in 417 tumors. This collection of samples included: 50 SS18/SSX1/2 fusion positive synovial sarcomas, 155 gastrointestinal stromal tumors (GIST), 135 other spindle cell sarcomas as well as 77 other sarcomas (chondrosarcoma, osteosarcoma, dedifferentiated liposarcoma, alveolar soft part sarcoma, rhabdomyosarcoma, angiosarcoma, malignant mesothelioma, and Ewing's sarcoma). We report that 76% of synovial sarcomas expressed NY-ESO-1 in a strong and diffuse pattern (2-3+, >50-70% of tumor cells). In contrast, only rare cases of other spindle cell mesenchymal tumor expressed NY-ESO-1 (GIST (2/155), malignant peripheral nerve sheath tumors (1/34), and dermatofibrosarcoma protuberans (2/20)). Individual cases of other sarcomas (angiosarcoma, malignant mesothelioma, chondrosarcoma, osteosarcoma, dedifferentiated liposarcoma, alveolar soft part sarcoma, and Ewing's sarcoma) were positive for NY-ESO-1. However, no positive cases were identified amongst our cohort of leiomyosarcomas (0/24), hemangiopericytoma/solitary fibrous tumors (0/40), and cellular schwannomas (0/17). In summary, we find that NY-ESO-1 is strongly and diffusely expressed in a majority of synovial sarcomas, but only rarely in other mesenchymal lesions. Beyond its role in patient selection for targeted therapy, immunohistochemistry for NY-ESO-1 may be diagnostically useful for the distinction of synovial sarcoma from other spindle cell neoplasms.     

What do we know about inflammatory myofibroblastic tumors? – A systematic review

BackgroundInflammatory myofibroblastic tumors (IMTs) are rare intermediate-grade neoplasms that have a high recurrence rate after excision and exhibit low metastatic potential. These tumors contain proliferating neoplastic, fibroblastic and myofibroblastic cells, and are also characterized by chronic inflammatory infiltration by lymphocytes, plasma cells, eosinophils, and histiocytes. They belong to the group of inflammatory spindle cell lesions. Some reactive lesions, such as inflammatory pseudotumors, may appear to be IMTs, which makes their differential diagnosis extremely difficult. The aim of this article is to compile the recent information on IMTs to aid in their diagnosis and treatment.MethodsWe reviewed articles published between 2017 and 2021, which were selected from online medical databases. In addition, some earlier articles and latest scientific monographies were analyzed.ResultsThe terminology used for inflammatory spindle cell lesions seems to be confusing. The terms “inflammatory myofibroblastic tumors” and “inflammatory pseudotumors” are interchangeably used by many scientists. However, a detailed analysis of the development of terminology suggests that the term “inflammatory myofibroblastic tumors” should be used to refer to a neoplastic lesion.ConclusionsIMTs are rare neoplasms, which have not been investigated in detail due to the difficulty in collecting a large number of cases. Thus, our knowledge about this disease remains unsatisfactory. Recently developed techniques such as next-generation sequencing and computer-aided histopathological diagnosis may be useful in understanding the etiopathology of IMTs, which will help in the selection of the most appropriate therapy for patients.     

D2-40 and podoplanin are highly specific and sensitive immunohistochemical markers of epithelioid malignant mesothelioma

Recent investigations have shown that podoplanin and the D2-40 monoclonal antibody, which reacts with an oncofetal antigen present in fetal germ cells, are highly reliable lymphatic endothelial markers. The observation that both of these markers are also expressed in normal and reactive mesothelial cells prompted an investigation into their potential value in the diagnosis of mesotheliomas. To determine whether podoplanin and D2-40 had any use in the diagnosis of these tumors, 40 mesotheliomas (29 epithelioid, 5 biphasic, and 6 sarcomatoid), 34 carcinomas of the lung (24 adenocarcinomas, 10 squamous carcinomas), 80 nonpulmonary adenocarcinomas (17 ovary, 10 breast, 10 colon, 10 kidney, 5 endometrium, 5 stomach, 5 pancreas, 5 prostate, 3 thyroid), 12 synovial sarcomas (6 biphasic and 6 monophasic), 5 angiosarcomas, and 2 adenomatoid tumors were immunostained with a monoclonal antibody to podoplanin and with the D2-40 antibody. Reactivity for both D2-40 and podoplanin was obtained in 25 (86%) of the 29 epithelioid mesotheliomas but in none of the carcinomas or sarcomatoid mesotheliomas. Positivity for D2-40 and podoplanin was also seen in the epithelioid components of 4 of 5 biphasic mesotheliomas and 4 of 6 synovial sarcomas, whereas the spindle cell components of these tumors were negative as were the monophasic synovial sarcomas. Two (40%) of the 5 angiosarcomas expressed these markers, thus confirming previous reports suggesting that some angiosarcomas may have lymphatic endothelial differentiation. Both of the adenomatoid tumors were also positive for D2-40 and podoplanin, a finding which provides further support for the mesothelial derivation of these tumors. It is concluded that, because of their high specificity and sensitivity for epithelioid mesotheliomas, D2-40 and podoplanin are very useful markers for the diagnosis of these tumors. When compared with the other markers that are currently available, in my opinion, they appear to be the best.     

Follicular dendritic cell sarcoma mimicking giant cell carcinoma of the pancreas

Extranodal follicular dendritic cell (FDC) tumors are rare. Recognition of the morphological spectrum of FDC tumors is important to clinical diagnosis. Herein is presented a case of pancreatic FDC sarcoma with unusual clinicopathological features. A 64-year-old male patient presented with weight loss, poor appetite, abdominal fullness, mild anemia and mild peripheral eosinophilia. Histologically, the tumor was composed of both epithelioid and spindle cells with abundant intracytoplasmic hyaline globules. These tumor cells were positive for CD21, CD23, CD35, S-100 protein, fascin and clusterin. Both epithelioid and spindle tumor cells independently colonized the liver and formed two tumor nodules 18 months after the initial resection. Notably, the two hepatic metastases additionally acquired patchy expression of human leukocyte antigen-DR. The epithelioid FDC in one of the hepatic lesions transformed into numerous bizarre giant cells, which could easily be confused with a metastatic giant cell carcinoma from the pancreas. FDC tumor should therefore be included in the differential diagnoses when dealing with a giant cell tumor.     

Splenic inflammatory myofibroblastic tumor (inflammatory pseudotumor): a clinicopathologic and immunophenotypic study of 12 cases

CONTEXT: Inflammatory pseudotumor is an uncommon and enigmatic lesion. The spindle cells found in this tumor have features of myofibroblasts. Because of the indefinite relationship of these lesions with inflammatory fibrosarcoma and their indefinite biologic behavior, inflammatory pseudotumor is currently classified as inflammatory myofibroblastic tumor (IMT). To date, only case reports or small series have been published on these tumors, which are primary in the spleen. DESIGN: In this study, we describe the clinical, morphologic, and immunophenotypic findings of 12 cases of splenic IMT and examine their relationship to Epstein-Barr virus (EBV). RESULTS: The patients included 8 women and 3 men, ranging from 19 to 77 years of age (mean, 53 years; median, 60 years). Demographic data were unavailable for 1 patient. Patients generally presented with abdominal pain (n = 5) and fever (n = 4). Associated lesions included renal cell carcinoma (n = 2), colonic adenocarcinoma (n = 1), and cholecystitis (n = 1). All tumors were composed of a bland spindle cell proliferation in association with a variable mixed inflammatory component. There were 2 growth patterns, namely, a cellular spindle cell pattern and a hypocellular fibrous pattern. An immunohistochemical panel confirmed the myofibroblastic nature of the spindle cells. The spindle cells of 2 cases were immunoreactive for EBV latent membrane protein 1, whereas 6 of 10 cases were positive for EBV-encoded RNA using in situ hybridization. Follow-up was available for 8 patients; 6 were alive with no evidence of recurrence and 2 were dead of other causes. CONCLUSION: Splenic IMTs are uncommon lesions that can be distinguished from other conditions using a combination of clinical, histologic, and immunophenotypic findings. Epstein-Barr virus may play a role in the pathogenesis of splenic IMT, and there may be an association of splenic IMT with concomitant disease or malignancy. Most splenic IMTs have an excellent long-term prognosis.     

Inflammatory myofibroblastic tumor of the central nervous system and its relationship to inflammatory pseudotumor

Inflammatory myofibroblastic tumor (IMT) is a distinctive spindle cell lesion and occurs primarily in soft tissue. Recent evidence suggests a neoplastic nature, although historically, both neoplastic and nonneoplastic processes were combined in this category. Originally described as a nonneoplastic process, the term inflammatory pseudotumor (IP) has been used synonymously with IMT. IMTs have been linked to ALK gene (2p23) rearrangements, and some have suggested an association with the human herpesvirus 8 (HHV-8). IMT in the central nervous system (CNS) is rare, its characteristics are poorly defined, and its relation to similar tumors at other sites is unclear. To better characterize IMT within the CNS, we studied clinicopathologic features of 6 IMTs and compared them with 18 nonneoplastic lesions originally classified as IP. The IMT group consisted of 2 male and 4 female patients with a median age of 29 years. Of the six IMTs, 5 occurred within the cerebral hemispheres, and one was in the posterior fossa. All tumors were composed of neoplastic spindle cells and a variable amount of inflammatory infiltrate. Eighteen IPs included in this study consisted of predominantly inflammatory masses occasionally seen in the setting of systemic diseases. Only 1 IMT and none of the IPs recurred during the follow-up period. Four IMTs had either ALK protein overexpression or 2p23 rearrangement, and 1 case demonstrated both. None of the IPs were positive for ALK. Neither IMT nor IP cases demonstrated HHV-8 expression. We suggest that IMT in the CNS is distinct from the nonneoplastic IP, and distinguishing IMT from nonneoplastic lesions should enable better decisions for patient management.     

A histiocyte-specific marker in the diagnosis of malignant fibrous histiocytoma. Use of monoclonal antibody KP-1 (CD68)

KP-1 (CD68) is a recently described monoclonal antibody to a cytoplasmic epitope present on tissue histiocytes and macrophages. To determine the specificity and sensitivity of this marker in the evaluation of cases of malignant fibrous histiocytoma (MFH), this reagent and a panel of commercially antibodies were used to stain formalin-fixed paraffin sections from 25 cases of MFH and 25 other tumors, including a variety of soft-tissue sarcomas. Eighteen of 25 cases of MFH stained for KP-1 (72%), whereas all other tumors were negative, including 12 cases of pleomorphic soft-tissue sarcoma other than MFH. The percentage of tumor cells staining for KP-1 varied. In 11 cases KP-1 was only focally present, but staining was of a high intensity and associated with minimal nonspecific or background staining. Pleomorphic histiocytic cells and spindle cells from storiform tumors were strongly decorated with antibodies to KP-1 in most cases, and antigen also was present on tumor giant cells. Although alpha-1-antitrypsin and alpha-1-chymotrypsin stained a higher percentage of cases of MFH (92%), immunoreactivity for these markers also was noted in other tumors. Because of its specificity as a histiocyte marker, KP-1 is a useful component in a panel of antibodies for the characterization of soft-tissue sarcomas and the diagnosis of MFH.