Use of Smooth Muscle Myosin Heavy Chain as an Effective Marker of Follicular Dendritic Cells.

Smooth muscle myosin heavy chain (SMMHC) is a major structural component of the contractile apparatus in smooth muscle cells. Even though it is considered a relatively specific marker for terminal smooth muscle cell differentiation, expression in other cell types such as follicular dendritic cells (FDCs) has rarely been reported. To determine whether SMMHC represents an effective FDC marker in lymphoid tissues, we compared the immunohistochemical results for SMMHC with those of the traditional FDC markers podoplanin (D2-40) and CD21. Paraffin sections of 44 lymphoid tissues were analyzed, including 31 cases of follicular hyperplasia, 6 cases of follicular lymphoma, 2 cases of peripheral T-cell lymphoma, 3 cases of diffuse large B-cell lymphoma arising in follicular lymphoma, 1 case of nodular sclerosis classical Hodgkin lymphoma, and 1 case of small lymphocytic lymphoma. There was no statistically significant difference between the number of SMMHC-positive and D2-40-positive or CD21 lymph nodes (P>0.05). The extent and intensity of SMMHC-positive FDCs were similar to those of D2-40-positive FDCs (P=0.127 and 0.733, respectively), but significantly lower compared with those of CD21 cells (P=0.009 and 0.00002, respectively). However, in contrast to CD21 which was also positive in some germinal center B cells, SMMHC expression was restricted to FDCs. Our results indicate that SMMHC is an excellent marker for FDCs and can be particularly helpful in demonstrating the underlying architecture in lymphoid processes.

Castleman disease. Histopathological and immunohistochemical analysis of 39 cases. / Enfermedad de Castleman. Análisis histopatológico e inmunohistoquímico de treinta y nueve casos.

Introduction: Castleman disease (CD) is a rare lymphoproliferative that comprises two distinct clinical subtypes (unicentric and multicentric) and has two basic histopathology patterns that are hyaline-vascular (HV) and plasma-cell (PC) type. Some cases of multicentric PC disease are associated with HHV-8 infection. Objective: To present the histopathologic and immunohistochemical characteristics of 39 cases of CD. Methods: A review of cases with the diagnosis CD from the files of the Department of Pathology of the ABC Medical Centre in Mexico City was performed. Thirty-nine cases of CD were identified, and a detailed paraffin immunophenotypic study of 9 of them was completed using desmin, cytokeratin OSCAR (CO) and Epidermal growth factor receptor (EGFR), to evaluate the dendritic cell population. Results and Conclusions: Of the 39 cases of CD, 24 were HV and 15 CP. All HV cases were unicentric and only one case of CP was multicentric. The most frequent localization in both subtypes was in lymph nodes; 21/24 cases in HV and 15 cases of CP. All cases were immunostained with CD20 that was expressed in the germinal centers (CGs), CD3 in the paracortical zone, and CD21 in follicular dendritic cells (CDF) within CGs, with expansion towards the area of the hyperplastic mantle zone (only in the HV variant). One case of CD CP was positive for HHV-8. Of the nine cases (6 HV and 3 PC cases) that were detailed with IHC, we found EGFR expression in FDC in all but one of the 9 cases studied and desmin was positive in fibroblastic reticulum cells (FRC) in all, but one of the cases of CD. CO was positive FRC in 3 of 6 cases of HV type and all (3) of the PC type. Clinical, histopathological and HIV and HHV-8 status markers, allow for the classification of CD into groups with markedly different outcomes and disease associations.

Inflammatory pseudotumor-like follicular dendritic cell tumor: an underdiagnosed neoplasia

Follicular dendritic cell (FDC) tumor is an uncommon neoplasm. It generally presents as a slow-growing, painless mass, without systemic symptoms. Histological features usually include low grade spindle cell proliferation. This tumor occurs primarily in lymph nodes, especially cervical and axillary, however, involvement of extranodal sites such as the tonsils, spleen, liver, and gastrointestinal tract has been reported. Inflammatory pseudotumor-like follicular dendritic cell tumor (IPT-like FDCT) is a rare, distinctive histological subtype of this low-grade malignant neoplasm, with consistent Epstein-Barr virus (EBV) association. The differential diagnosis with other fibro-inflammatory tumor proliferations, as inflammatory pseudotumor (IPT) and inflammatory myofibroblastic tumor (IMT), may be challenging. In the present article, two cases of IPT-like FDCT of the spleen are presented, with a broad overview of the literature: one 77-year-old male and one 70-year-old female. A large immunohistochemical panel should be used for diagnosis, as no single specific and totally sensitive markers are available, including markers for CD21, CD23, CD35, CNA42, and clusterin. Individual cases may express one or more of these markers, so that all of them should be investigated. In situ hybridization for EBV is constantly positive. Immunostaining for ALK should be negative, as it is present in roughly half of the cases of IMT. This panel should be used in combination of clinical, laboratory, and topographic evidences. Importantly, inclusion of this lesion as a possible option in clinical and pathological investigation represents the basis for a correct diagnosis (AU)

Cellular composition of the tumor microenvironment.

In addition to malignant cells, the tumor microenvironment also includes nonmalignant cells, secreted proteins, and blood vessels that surround and support the growth of the tumor. Interactions between the various components of the tumor microenvironment are significant; tumor cells can change the nature of the microenvironment, and conversely, the microenvironment can affect how a tumor grows and spreads. The structure and composition of the tumor microenvironment varies among different types of cancers and between patients. This paper focuses on the composition and function of the tumor microenvironment in hematologic malignancies with a specific focus on B-cell lymphomas.

Comparison of the larynx-associated lymphoid tissue in the false vocal cords and subglottis in pediatric autopsies.

The aim this work was to compare the distribution of cellular phenotypes of the LF in the FVC to the ones in the subglottic region in pediatric autopsy, relating this distribution to age and different causes of death. We analyzed 60 larynges of newborns and children autopsied in the period from 1993 to 2003. The fragments were prepared in order to perform histochemical and immunohistochemical techniques. The morphological analysis showed cases that presented LF only in FVC (35%), LF only in the subglottic region (20%), lack of LF in FVC (30%) and lymphoid aggregates, which did not characterize an LF (15%). The cases of LF in the subglottic region were significantly younger compared to the ones that presented LF in the FVC (p=0.017). The LF in the subglottic region was bigger than the LF in the FVC (p=0.020). There was no significant difference between the cause of death and cellular phenotype for both FVC and the subglottic region. In conclusion, the cells that make up the LF in the FVC in newborns and children younger than one year have functional characteristics similar to LF cells in the subglottic region, suggesting that there are similarities with LALT.

Immunohistochemical analysis for CD21, CD35, Caldesmon and S100 protein on dendritic cells types in oral lymphomas

OBJECTIVE: Follicular dendritic cells (FDCs) and interdigitating dendritic cells (IDCs) are dendritic cells found in lymphoid follicles, reactive follicles and in lymphomas. The goal of this study was to evaluate the presence and distribution of FDCs and IDCs in oral lymphomas. MATERIAL AND METHODS: Immunohistochemistry reactions were applied to 50 oral lymphomas using the antibodies anti-CD21, anti-CD35 and anti-caldesmon to FDCs, and anti-S100 protein to IDCs. Caldesmon+/FDCs and S100+/IDCs were quantified in Imagelab® software. RESULTS: FDCs revealed by CD21 and CD35 were positively stained in two cases of diffuse large B-cell lymphoma, one MALT lymphoma, and in one case of mantle cell lymphoma. FDCs were immunopositive to caldesmon in all cases, as well as IDCs to S100 protein. Burkitt lymphoma presented a lower amount of caldesmon+/FDCs and S100+/IDCs than diffuse large B-cell lymphoma and plasmablastic lymphoma of the oral mucosa type. CONCLUSIONS: The microenvironment determined by neoplastic lymphoid cells in oral lymphomas is responsible by the development and expression of dendritic cells types.

Immunohistochemical analysis for CD21, CD35, Caldesmon and S100 protein on dendritic cells types in oral lymphomas.

OBJECTIVE: Follicular dendritic cells (FDCs) and interdigitating dendritic cells (IDCs) are dendritic cells found in lymphoid follicles, reactive follicles and in lymphomas. The goal of this study was to evaluate the presence and distribution of FDCs and IDCs in oral lymphomas. MATERIAL AND METHODS: Immunohistochemistry reactions were applied to 50 oral lymphomas using the antibodies anti-CD21, anti-CD35 and anti-caldesmon to FDCs, and anti-S100 protein to IDCs. Caldesmon+/FDCs and S100+/IDCs were quantified in Imagelab software. RESULTS: FDCs revealed by CD21 and CD35 were positively stained in two cases of diffuse large B-cell lymphoma, one MALT lymphoma, and in one case of mantle cell lymphoma. FDCs were immunopositive to caldesmon in all cases, as well as IDCs to S100 protein. Burkitt lymphoma presented a lower amount of caldesmon+/FDCs and S100+/IDCs than diffuse large B-cell lymphoma and plasmablastic lymphoma of the oral mucosa type. CONCLUSIONS: The microenvironment determined by neoplastic lymphoid cells in oral lymphomas is responsible by the development and expression of dendritic cells types.

Morphological characterization of the false vocal cords as larynx-associated lymphoid tissue.

The lymphoid follicles (LF) found in the false vocal cords (FVC) protect the upper air tracts, similar to the lymphoid tissue associated to the respiratory mucosas. However, studies that characterize the phenotype of cells like larynx-associated lymphoid tissue (LALT) are lacking. We analyzed the FVC of autopsied adults according to morphometric and immunohistochemical criteria and defined their possible role as LALT. We analyzed 249 FVC. Primary antibodies, CD68+ macrophages, CD20+, CD3+, and FDC+ were used for the evaluation of inflammatory cell phenotypes. In 40.6% of the cases, there was an inflammatory reaction. In 42.2% of the cases, LF were identified in the submucosa. In 17.3% of the cases, neither LF nor mononuclear cells were identified in the FVC, and these patients were from an older age group (p=0.013). A significant increase in the number of all LF cell phenotypes was observed in patients with pulmonary inflammation; the difference in both T- and B-lymphocytes was statistically significant (p=0.010). The morphological findings of LF suggest a probable participation of the FVC in the protection of the larynx and lungs, and similarity to LALT.

Immunological evaluation of vestibular folds in autopsies of patients with the acquired immunodeficiency syndrome.

UNLABELLED: Immune response cells are decreased in patients with the Acquired Immunodeficiency Syndrome. This alters the cell population in vestibular fold lymphoid follicles, leading to respiratory infections in these patients. Such infections are the main cause of mortality and morbidity in these patients. AIM: to characterize lymphoid follicle cell populations in the vestibular folds of adults with the Acquired Immunodeficiency Syndrome and associated or not respiratory infection. MATERIALS AND METHODS: A retrospective study was made of 64 adult larynges harvested during routine autopsies. Anti-B cell, Anti-CD3, Anti-CD68 and Anti-follicular dendritic cell antibodies were used for immunological testing. RESULTS: 46 (71.87%) of the sample patients had the Acquired Immunodeficiency Syndrome. In these patients, lymphoid follicle cellularity was lower compared to the control group. The cell number was decreased in patients with the Acquired Immunodeficiency Syndrome and associated respiratory tract infection. CONCLUSION: We demonstrated in this study that vestibular fold lymphoid follicles were affected by viral infections, and may be considered as a reliable marker of immunodepression in these patients.

Avaliação imunológica nas pregas vestibulares de pacientes autopsiados com a Síndrome da Imunodeficiência Adquirida / Immunological evaluation of vestibular folds in autopsies of patients with the Acquired Immunodeficiency Syndrome

Em pacientes com Síndrome da Imunodeficiência Adquirida há uma diminuição das células envolvidas na resposta imune, o que influencia na população celular dos folículos linfóides encontrados nas pregas vestibulares, favorecendo o aparecimento de infecções nas vias aéreas destes pacientes. Estas infecções são a principal causa de mortalidade e morbidade nestes pacientes. OBJETIVO: Caracterizar a população de células nos folículos linfóides localizados nas pregas vestibulares de adultos autopsiados com Síndrome da Imunodeficiência Adquirida, com e sem infecções respiratórias associadas. MATERIAIS E MÉTODOS: Foi realizado um estudo retrospectivo transversal em 64 laringes de adultos coletadas na rotina das autopsias. Para a imunohistoquímica foram utilizados os anticorpos: Anti-B cells, Anti-CD3, Anti-CD68 e Anti-follicular dendritic cells. RESULTADOS: 46 (71,87 por cento) dos pacientes estudados tinham diagnóstico de Síndrome da Imunodeficiência Adquirida. Nestes pacientes, a celularidade dos folículos linfóides foi estatisticamente menor em relação ao grupo controle em todos os fenótipos estudados. Nos pacientes imunodeprimidos com infecção respiratória associada, o número de células estava diminuído, sendo significante no caso dos linfócitos T (p=0,024). CONCLUSÃO: Em nosso estudo demonstramos que os folículos linfóides das pregas vestibulares são afetados pela infecção viral e representam com fidedignidade o estado imunológico de imunodepressão destes pacientes.

Immune response cells are decreased in patients with the Acquired Immunodeficiency Syndrome. This alters the cell population in vestibular fold lymphoid follicles, leading to respiratory infections in these patients. Such infections are the main cause of mortality and morbidity in these patients. AIM: to characterize lymphoid follicle cell populations in the vestibular folds of adults with the Acquired Immunodeficiency Syndrome and associated or not respiratory infection. MATERIALS AND METHODS: A retrospective study was made of 64 adult larynges harvested during routine autopsies. Anti-B cell, Anti-CD3, Anti-CD68 and Anti-follicular dendritic cell antibodies were used for immunological testing. RESULTS: 46 (71.87 percent) of the sample patients had the Acquired Immunodeficiency Syndrome. In these patients, lymphoid follicle cellularity was lower compared to the control group. The cell number was decreased in patients with the Acquired Immunodefficiency Syndrome and associated respiratory tract infection. CONCLUSION: We demonstrated in this study that vestibular fold lymphoid follicles were affected by viral infections, and may be considered as a reliable marker of immunodepression in these patients.

Intra-abdominal follicular dendritic cell sarcoma with marked pleomorphic features and aberrant expression of neuroendocrine markers: report of a case with immunohistochemical analysis.

Follicular dendritic cell sarcoma (FDCS) is a very rare malignant tumor arising most frequently in lymph nodes with only few reports of extranodal locations. We report the case of a 35-year-old man with a large retroperitoneal mass. Histologically the tumor was composed of highly pleomorphic cells exhibiting some uncommon features such as an epithelioid appearance, cystic spaces, and multinucleated cells with morphologic features of emperipolesis. Immunohistochemically the neoplastic cells were immunoreactive for CD21, CD23 and CD35. A previously unreported expression of neuroendocrine markers (Synaptophisyn and Neuron-Specific-Enolase) was present. Ultrastructurally no neuroendocrine secretory granules were detected. FDCS can mimic a wide variety of other malignant tumors, and a correct diagnosis requires exclusion of other neoplasms and immunohistochemical confirmation.

Intra-abdominal follicular dendritic cell sarcoma.

Follicular dendritic cell (FDC) sarcoma is a very rare condition. We report here an intra-abdominal FDC sarcoma occurring as a mass, dependent on the celiac and left gastric lymph chains, that was completely excised. Eighteen months after surgery a recurrence at the liver pedicle was detected by a CT-scan and fully resected; in order to prevent another disease relapse postoperative radiotherapy was given.

Evidence for melano-macrophage centres of teleost as evolutionary precursors of germinal centres of higher vertebrates: an immunohistochemical study.

The melano-macrophage centres (MMCs) of the haemolymphopoietic organs of teleost fish trap and retain antigens and are closely associated with immunoglobulin-secreting cells. The hypothesis that they are the phylogenetic precursors of the germinal centres of higher vertebrates has been questioned due to their apparent lack of organising cells. In this study the immunoreactivity of MMC cells from spleen and kidney of the teleosts Cyprinus carpio, Odontesthes bonariensis and Solea senegalensis to CNA-42, an antibody usually employed for labelling follicular dendritic cells of higher vertebrates was investigated. Free melano-macrophages and MMCs in the spleens of all three species were labelled by the antibody. This finding adds new evidence to the hypothesis that an evolutionary relationship exists between the MMCs of fish and the germinal centres of many birds and mammals.

Células dendríticas foliculares: imunofenotipagem no linfoma de Hodgkin clássico esclerose nodular / Dendritic follicular cells: immunophenotyping in classic Hodgkin's lymphoma nodular sclerosis

O linfoma de Hodgkin clássico esclerose nodular (LHCEN), de origem linfóide da célula B do centro germinativo (CG), apresenta agregados de células dendríticas foliculares (CDF), célula Hodgkin/Reed Sternberg e variantes, células B formando complexos relacionados ao CG, sugerindo uma associação entre esclerose nodular e formação do centro germinativo. O objetivo desse estudo foi avaliar a célula dendrítica folicular, por imunofenotipagem com o anticorpo fascina, em biópsia de linfonodo periférico ou massa do mediastino de pacientes com LHCEN previamente diagnosticados, procurando identificar critérios como fatores prognósticos. Foram selecionados 38 pacientes, 55,2 por cento do sexo masculino com relação M:F de 1,23: 1 e a idade com média de 29,3 anos; 52,6 por cento em estádios clínicos I-II, sendo 68,4 por cento com sintomas B. Foram analisados 38 espécimes de biópsias, sendo 57,9 por cento do subtipo esclerose nodular II. O estudo imuno-histoquímico mostrou 100 por cento de positividade para o CD30 e 68,4 por cento para o CD15. As CDFs foram identificadas pelo anticorpo fascina, considerado padrão-ouro, através da técnica imunoenzimática indireta peroxidase-anti-peroxidase estreptavidina-avidina-biotina (PAP-Strept ABC), realizada em lâminas pré-tratadas do material de biópsia incluído em blocos de parafina. Foi evidenciado padrão CDF1 em 7,9 por cento, CDF2 em 47,4 por cento e CDF3 em 44,7 por cento. Não houve relação entre a presença da CDF e sexo, idade, estádio clínico e resposta ao tratamento, mas foi demonstrada uma tendência para associação (p=0,056) entre CDF os subtipos LHCEN. Os pacientes com presença de célula dendrítica folicular foram acompanhados por maior período, com média de 32,9 meses, com associação estatisticamente significativa (p=0,001).

Classic nodular sclerosis HodgkinÆs lymphoma (CNSHL) is a lymphoid neoplasm of germinal center (GC) B cells, presenting with aggregates of follicular dendritic cells (FDC), Hodgkin/Reed Sternberg cells and variants and B cells forming complexes related to the GC. This suggests an association between nodular sclerosis and GC formation. The goal of this study was to evaluate the follicular dendritic cells by immunophenotyping with fascin from lymph node or mediastinal mass biopsies of patients previously diagnosed as having CNSHL, in order to attempt to identify criteria as prognostic factors. Thirty-eight patients were selected. A total of 55.2 percent were male with a M:F ratio of 1.23:1 and a mean age of 29.3 years. 52.6 percent were in clinical stage I-II and 68.4 percent had symptoms B. Thirty-eight biopsy specimens were analysed and 57.9 percent were nodular sclerosis II. Immuno­phenotyping showed 100 percent positivity for CD30 and 68.4 percent for CD15. The FDC were identified by fascin, using the peroxidase-antiperoxidase streptavidin-avidin-biotin indirect immuno­enzimatic technique, which was performed on pre-treated slides with the biopsy specimens embedded in paraffin blocks. Fascin was considered to be the gold-standard. The CDF1 pattern was present in 7.9 percent, CDF2 in 47.4 percent and CDF3 in 44.7 percent. There was no association between the presence of the FDC and gender, age, clinical stage, response to treatment, but a tendency for association (p=0.056) between the subtypes of CNSHL. Patients with FDC present in their biopsies were followed up for a longer period of time - about 32.9 months. This enabled a significant statistical association (p=0.001) between the presence of FDC and length of follow-up.

Las lesiones iniciales del linfoma de Hodgkin clásico de tipo esclerosante nodular / Early lesions in classical Hodgkin lymphoma of the nodular

All patients with Hodgkins disease should at minimum, undergo staging evaluation. The staging system that has developed in an effort to distinguish patients with different prognose in an anatomic staging system that generally corelates with the tumor burden. In this article the authors describe the early lymph nodes involvement,with a study of patients whose disease has spread to the spleen. Special interest has focused in the study of the early lesions for the complete understanding of the concept of the classical Hodgkin lymphoma

Las lesiones iniciales del linfoma de Hodgkin clásico de tipo esclerosante nodular / Early lesions in classical Hodgkin lymphoma of the nodular

All patients with Hodgkin's disease should at minimum, undergo staging evaluation. The staging system that has developed in an effort to distinguish patients with different prognose in an anatomic staging system that generally corelates with the tumor burden. In this article the authors describe the early lymph nodes involvement,with a study of patients whose disease has spread to the spleen. Special interest has focused in the study of the early lesions for the complete understanding of the concept of the classical Hodgkin lymphoma

Los priones, un nuevo desafío evolutivo / Prions: a new evolutionary defiance

El objetivo de esta reseña es actualizar información ya publicada sobre los priones y las patologías que éstos transmiten. La existencia de una nueva variante de la enfermedad de Creutzfeld-Jakob y la confirmación experimental de que es causada por la misma cepa de priones que la encefalopatía espongiforme bovina (BSE), ha incrementado dramáticamente la necesidad de una precisa comprensión de las bases moleculares de la propagación priónica. El agente infeccioso es una proteína cuya conformación se encuentra alterada, que se reproduce a sí misma convirtiendo una proteína normal en una proteína con conformación priónica. La observación de que los priones se replican en los órganos linfoides en estadios muy tempranos de la infección lleva a cuestionar sobre cuáles son los requerimientos de tipo celular a ser infectado en el sistema linforreticular. Las células dendríticas foliculares serían el sitio de elección para la replicación y el reservorio de priores. El diagnóstico de las enfermedades producidas por priones presenta una serie de problemas debido a las peculiaridades de este tipo de patologías. Considerando que los priones se replican en el sistema linforreticular y posteriormente migran al sistema nervioso central, existe un lapso durante el cual podría propagarse este agente infeccioso por medio de la sangre, sus componentes o sus derivados. De esta forma representaría una nueva patología con la potencial capacidad de transmisión transfusional. Esta nueva forma de herencia independiente de los ácidos nucleicos obliga a replantear el axioma de transferencia de la información genética, hasta el momento, y con concordancia con la teoría evolutiva de Darwin, sólo pensando mediante moléculas constituidas por nucleótidos. ¿Será tiempo de cambiar el paradigma?

Los priones, un nuevo desafío evolutivo / Prions: a new evolutionary defiance

El objetivo de esta reseña es actualizar información ya publicada sobre los priones y las patologías que éstos transmiten. La existencia de una nueva variante de la enfermedad de Creutzfeld-Jakob y la confirmación experimental de que es causada por la misma cepa de priones que la encefalopatía espongiforme bovina (BSE), ha incrementado dramáticamente la necesidad de una precisa comprensión de las bases moleculares de la propagación priónica. El agente infeccioso es una proteína cuya conformación se encuentra alterada, que se reproduce a sí misma convirtiendo una proteína normal en una proteína con conformación priónica. La observación de que los priones se replican en los órganos linfoides en estadios muy tempranos de la infección lleva a cuestionar sobre cuáles son los requerimientos de tipo celular a ser infectado en el sistema linforreticular. Las células dendríticas foliculares serían el sitio de elección para la replicación y el reservorio de priores. El diagnóstico de las enfermedades producidas por priones presenta una serie de problemas debido a las peculiaridades de este tipo de patologías. Considerando que los priones se replican en el sistema linforreticular y posteriormente migran al sistema nervioso central, existe un lapso durante el cual podría propagarse este agente infeccioso por medio de la sangre, sus componentes o sus derivados. De esta forma representaría una nueva patología con la potencial capacidad de transmisión transfusional. Esta nueva forma de herencia independiente de los ácidos nucleicos obliga a replantear el axioma de transferencia de la información genética, hasta el momento, y con concordancia con la teoría evolutiva de Darwin, sólo pensando mediante moléculas constituidas por nucleótidos. ¿Será tiempo de cambiar el paradigma?

Fine-needle aspiration of a follicular dendritic-cell tumor: report of a case and review of the literature.

Follicular dendritic-cell tumors (FDCT) are rare neoplasms, well-characterized in surgical pathology material. There are, however, few cytopathology reports. We describe the fine-needle aspiration (FNA) findings of a histologically confirmed FDCT. Conventional smears and a cell block showed large spindle to oval neoplastic cells admixed with small mature lymphocytes. The neoplastic cells were present mainly in small syncytial clusters. Immunostains for CD21 and CD35, performed on the cell block, were positive in the neoplastic cells. The diagnosis was fully confirmed by the presence of typical immunohistochemical and ultrastructural features on the surgically removed tumor. The differential diagnosis of FDCT is broad and includes other tumors characterized by an admixture of large neoplastic cells and small mature lymphocytes, such as thymomas, lymphoepithelioma-like carcinomas, and interdigitating dendritic-cell tumors. It may not be possible to diagnose FDCT based on FNA material without the use of immunocytochemical and electron microscopic studies. Certain cytomorphological characteristics, however, might suggest its diagnosis and allow the practicing cytopathologist to perform confirmatory studies.