Immunoreactive cytokeratins in plasmacytomas

The many faces of plasma cell neoplasms: morphological and immunophenotypical variants of the great imitator

Plasma cell neoplasms are notorious for having diverse morphological presentations, and less frequently, unusual immunophenotypical profiles. This unexpected immunomorphological variability could lead to erroneous impressions upon initial assessment, potentially delaying the generation of a final accurate diagnosis. In this review, we present a concise, yet comprehensive summary of both morphological and immunophenotypical variants of plasma cell neoplasms from the archives of MD Anderson Hematopathology Department, with emphasis on possible diagnostic pitfalls precluding a timely and accurate assessment.

Cytokeratin expression in plasmablastic lymphoma - a possible diagnostic pitfall in the routine work-up of tumours

AIMS

Plasmablastic lymphoma (PBL) is a rare aggressive B-cell lymphoma that frequently arises at extranodal sites in the setting of immunosuppression. The diagnosis of PBL is complex, owing to a frequent solid or cohesive growth pattern, and an often unusual immunophenotype. Several case reports have described cytokeratin (CK) expression in PBL, introducing a diagnostic pitfall. The aim of this study was to determine the frequency of CK expression in PBL in the largest series available to date.

METHODS AND RESULTS

By using immunohistochemistry in a cohort of 72 PBLs, we identified CK8/18 positivity in 11 of 72 cases (15%) and AE1/3 positivity in six of 65 cases (9%), clearly contrasting with a control series of non-PBL aggressive B-cell lymphomas (one of 96 diffuse large B-cell lymphomas), as well as with data in the literature describing only occasional CK expression in haematological neoplasms.

CONCLUSIONS

Our data indicate CK expression in a substantial number (15%) of PBLs. In view of the particular morphological features of PBL and its frequent negativity for the common leukocyte antigen and B-cell markers, this feature represents a pitfall in the routine diagnostic work-up of PBL, and requires more extensive immunohistochemical and molecular characterisation of cases entering the differential diagnosis.

An Algorithmic Immunohistochemical Approach to Define Tumor Type and Assign Site of Origin

Immunohistochemistry represents an indispensable complement to an epidemiology and morphology-driven approach to tumor diagnosis and site of origin assignment. This review reflects the state of my current practice, based on 15-years' experience in Pathology and a deep-dive into the literature, always striving to be better equipped to answer the age old questions, "What is it, and where is it from?" The tables and figures in this manuscript are the ones I "pull up on the computer" when I am teaching at the microscope and turn to myself when I am (frequently) stuck. This field is so exciting because I firmly believe that, through the application of next-generation immunohistochemistry, we can provide better answers than ever before. Specific topics covered in this review include (1) broad tumor classification and associated screening markers; (2) the role of cancer epidemiology in determining pretest probability; (3) broad-spectrum epithelial markers; (4) noncanonical expression of broad tumor class screening markers; (5) a morphologic pattern-based approach to poorly to undifferentiated malignant neoplasms; (6) a morphologic and immunohistochemical approach to define 4 main carcinoma types; (7) CK7/CK20 coordinate expression; (8) added value of semiquantitative immunohistochemical stain assessment; algorithmic immunohistochemical approaches to (9) "garden variety" adenocarcinomas presenting in the liver, (10) large polygonal cell adenocarcinomas, (11) the distinction of primary surface ovarian epithelial tumors with mucinous features from metastasis, (12) tumors presenting at alternative anatomic sites, (13) squamous cell carcinoma versus urothelial carcinoma, and neuroendocrine neoplasms, including (14) the distinction of pheochromocytoma/paraganglioma from well-differentiated neuroendocrine tumor, site of origin assignment in (15) well-differentiated neuroendocrine tumor and (16) poorly differentiated neuroendocrine carcinoma, and (17) the distinction of well-differentiated neuroendocrine tumor G3 from poorly differentiated neuroendocrine carcinoma; it concludes with (18) a discussion of diagnostic considerations in the broad-spectrum keratin/CD45/S-100-"triple-negative" neoplasm.

[Space-occupying lesion in the maxillary sinus]

During the preoperative diagnostics of an 80-year-old male patient prior to a planned endarterectomy, an unclear space-occupying lesion was detected in the right nasopharyngeal cavity. It proved to be a dense soft tissue space-occupying lesion of the right maxillary sinus. The histological investigations revealed a partially necrotically decomposed malignant tumor below normal respiratory mucosa free from dysplasia. This case demonstrates the difficulties in differential diagnostics, particularly involving (aberrant) expression of cytokeratin.

Plasmacytoma with Aberrant Expression of Myeloid Markers, T-cell Markers, and Cytokeratin

Plasmacytomas are localized neoplastic proliferations of monoclonal plasma cells. When multifocal, the process is referred to as multiple myeloma. These lesions exhibit a pattern of antigen expression and cytomorphology that usually leads to a ready diagnosis. However, potentially troublesome variations in immunophenotype occur. We describe a case of a plasmacytoma from a patient who presented with sudden onset of pain and a lytic lesion of the left proximal humerus. Hematoxylin and eosin-stained sections showed a lymphoproliferative lesion composed of large lymphoid cells, some with plasmacytoid and immunoblastic features. The lesion also showed significant mitotic activity. Immunohistochemical staining was positive for CD45 (LCA), CD56 (N-CAM), CD43 (MT1), and cytokeratin CAM5.2. There was also clonal staining for λ light chains. In addition, flow cytometric analysis showed positivity for myeloid markers such as CD13, CD33, CD38, and CD138. Significant negative markers include CD20 (L26), CD45RO (UCHL-1), and CD79α. The unusual phenotypic features of this plasmacytoma illustrate potential diagnostic pitfalls. It is important to fully study such lesions to correctly classify them, because this has significant impact on prognosis and management.

Chronic idiopathic myelofibrosis terminating in extramedullary anaplastic plasmacytoma

Chronic idiopathic myelofibrosis (CIMF) is a chronic myeloproliferative disorder (CMPD) with progressive fibrosis and extramedullary hematopoiesis. Similar to other CMPDs, the stem cell in CIMF has the potential to differentiate into myeloid or lymphoid lineages, and thus CIMF can culminate in acute leukemia of myeloid or, rarely, lymphoid lineage. We describe an unusual case of CIMF terminating in extramedullary anaplastic plasmacytoma. The patient was a 61-year-old male with an 11-year history of CIMF. His course was complicated by rapidly growing abdominal and inguinal lymphadenopathy. Lymph node biopsy revealed a diffuse undifferentiated infiltrate in the background of extramedullary hematopoiesis. Flow cytometric and immunohistochemical analysis demonstrated plasma cell-related antigens (CD138, CD38, cytoplasmic kappa light chain), epithelial membrane antigen and CD43 in the tumor cells. The myeloid, B-cell or T-cell markers were negative. A clonal immunoglobulin heavy chain gene rearrangement was identified by polymerase chain reaction. The plasma cell origin was further confirmed by electron microscopic examination, which revealed stacks of rough endoplasmic reticulum. Monoclonal gammopathy may occur in CIMF, and rare cases of simultaneous plasma cell myeloma and CIMF have been reported in the literature. However, to the best of our knowledge, this is the first report of CIMF terminating in extramedullary anaplastic plasmacytoma.

Histology and immunohistology of bone marrow biopsy in multiple myeloma

B5-fixed/paraffin-embedded Jamshidi needle biopsies from 125 multiple myeloma patients were reviewed according to both morphological and immunohistological criteria. At microscopic examination, the following parameters were evaluated: i) grade of malignancy (low = 56; intermediate = 50; high = 19); ii) growth pattern (interstitial +/- sheets/nodules = 90; nodular = 13; packed marrow = 18; sarcomatous = 4); III) histological stage (I = 64; II = 35; III = 26). Comparison of the findings in trephine biopsies and aspirates showed that in 30% of the cases the latter led to an underestimation of the tumor burden. Immunohistochemical determination of Ig easily allowed: i) differential diagnosis from exuberant reactive plasmacytosis; ii) recognition and counting of neoplastic plasma cells; iii) detection of minimal residual disease after treatment. Immunohistochemistry also confirmed phenotypic aberration of neoplastic plasma cells, showing positivity for CD45, EMA, and cytokeratins in 14%, 59%, and 25% of the cases, respectively. Furthermore, it displayed expression of the P-glycoprotein in 4/8 resistant cases. These findings underline that routinely processed Jamshidi needle biopsies can be of great value in the study of patients with multiple myeloma.

Cytokeratin expression in hematological neoplasms: a tissue microarray study on 866 lymphoma and leukemia cases

Aberrant expression of cytokeratins (CK) is known to occasionally occur in malignant lymphomas. The monoclonal mouse-anti-human CK cocktail CK22 recognizes keratin polypeptides with a wide range of molecular weights and can be applied in diagnostic panels for tumors of unknown origin. Using tissue microarray technology, we tested 1059 lymphoma and acute leukemia cases, covering the most common disease entities, for aberrant CK expression, using CK22. In total, 866 of the arrayed cases were evaluable (80%), and 13 positive cases (1.5%) were found: 1 out of 230 Hodgkin lymphomas (0.4%), 1 plasma cell myeloma, 2 out of 326 diffuse large B-cell lymphomas (0.6%), 5 out of 18 mantle cell lymphomas (26%), 3 out of 70 small cell lymphomas/chronic lymphocytic leukemias (4%) and 1 out of 27 peripheral T-cell lymphomas, not otherwise specified (4%). Immunostaining was finely granular in most cases, and the total amount of positively staining cells exceeded 10% only in the cases of Hodgkin lymphoma and plasmocytoma. All CK22-positive cases, except for one mantle cell lymphoma, expressed the specific simple epithelial CK8 but not the basal/stratified epithelial CK5/6. Aberrant CK expression can be encountered in a small subset of otherwise characteristic B- and T-cell lymphomas, but not in acute leukemias, which should be considered in difficult differential diagnostic settings.

Undifferentiated tumor: true identity by immunohistochemistry

CONTEXT

"Undifferentiated tumor" refers to a heterogeneous group of neoplasms with little or no evidence of differentiation on routine light microscopic morphology.

OBJECTIVE

To identify the true identity of undifferentiated tumors by immunohistochemical analysis.

DATA SOURCES

Review of the pertinent literature and the authors' experience.

CONCLUSIONS

For treatment and prognostic evaluation, it is crucial to delineate whether an undifferentiated neoplasm is epithelial, mesenchymal, melanocytic, or hematopoietic in nature. Application of a screening panel to demonstrate the expression of markers of major lineages is fundamental for determination of the broad category of neoplasia. Because poorly differentiated carcinomas and in particular sarcomatoid carcinomas are known to be heterogeneous in their antigen expression, several epithelial markers in combination may be required to establish the carcinomatous nature of tumor. A diagnostic misinterpretation as a consequence of occasional aberrant or unexpected antigen expression is best avoided by using a broad panel that includes both antibodies that are anticipated to be positive and those that are expected to be negative. In this treatise, the immunohistochemical dissection of undifferentiated tumors on the basis of their morphologic features is outlined, supplemented with algorithmic immunohistochemical analysis for each morphologic category of small round cell tumors, carcinomatous tumors, sarcomatous (or sarcoma-like) tumors, and tumors with histologically overlapping features, including hematolymphoid malignancies, melanoma, and sarcomas with epithelioid appearance. The utility of several organ- or tissue-specific markers in the context of undifferentiated tumors is reviewed.

Keratin expression in human tissues and neoplasms

Keratin expression in human tissues and neoplasms Keratin filaments constitute type I and type II intermediate filaments (IFs), with at least 20 subtypes named keratin 1-20. Since certain keratin subtypes are only expressed in some normal human tissues but not others, and vice versa, various tissues have been subclassified according to the pattern of keratin staining. Simple epithelia generally express the simple epithelial keratins 7, 18, 19, and 20, while complex epithelia express complex epithelial keratins 5/6, 10, 14, and 15. When an epithelium undergoes malignant transformation, its keratin profile usually remains constant. The constitution and expression patterns of keratin filaments in human epithelial neoplasms are complex and often distinctive. In this article, we first briefly review the molecular and cell biology of keratin filaments. We then focus on the expression patterns of keratin filaments in various human neoplasms.

A comparison of epithelial membrane antigen overexpression in benign and malignant endometrium

OBJECTIVE

The aim of this study was to analyze the value of epithelial membrane antigen (EMA) overexpression in benign and malignant endometrium and its prognostic significance.

METHODS

EMA immunostaining was performed in 178 paraffin-embedded specimens including 105 endometrial cancers, 40 endometrial hyperplasias, and 33 benign endometriums. EMA immunostaining was correlated with traditional prognostic factors and progression-free survival in endometrial cancer specimens.

RESULTS

EMA overexpression was observed more frequently in adenocarcinomas (60%) than in hyperplasias (15%) or benign endometrium (9.1%). EMA overexpression was observed in two patients with endometrial hyperplasia who progressed to carcinoma. In adenocarcinomas, EMA overexpression had a positive correlation with nonendometrioid subtypes (P = 0.012). In multivariate analysis, FIGO stage (P = 0.025) and EMA overexpression (P = 0.017) were independent prognostic factors for progression-free survival.

CONCLUSIONS

EMA overexpression appears to be a marker of malignant transformation in the endometrium and it is an independent predictor of recurrent disease in endometrial cancer.

A case of keratin-positive acute myeloid leukemia: a possible role for cytokeratin 19 as a specific epithelial marker

A patient with relapsed acute myelomonocytic leukemia (AML, FAB M4) developed skin infiltration by leukemic blasts. On immunochemistry, the blasts showed "bot" positive cytoplasmic staining for cytokeratins AE1/AE3 and CAM 5.2, resembling the pattern seen in Merkel cell carcinoma of skin. However, the blasts were positive for myeloid markers and negative for cytokeratin 19 and chromogranin. Aberrant immunochemical staining can lead to misdiagnosis unless a panel of antibodies of known specificity is used in tumor diagnosis, and the clinical context is taken into account. The possible role of cytokeratin 19 as a more specific marker for epithelia than keratin cocktails is discussed.

Expression of MUC-1 glycoprotein in plasma cells, follicular dendritic cells, myofibroblasts and perineurial cells: immunohistochemical analysis using three monoclonal antibodies

Normal and malignant plasma cells (PC), follicular dendritic cells (FDC), myofibroblasts (MFB) and perineurial cells (PNC) were investigated for the expression of MUC-1 glycoprotein (MUC-1gp) by immunohistochemical and immunoelectron microscopic techniques using monoclonal antibodies E29, 115D8, DF3 and a combination of the three. MUC-1 glycoprotein-positive PC detected by the combined antibodies were frequently seen in a variety of pathological lesions tested, including chronic cervicitis, chronic synovitis, Hodgkin's disease, allergic rhinitis and sinusitis, tuberculous lymphadenitis, foreign body granuloma, multiple myeloma, and chronic tonsillitis. In the lesions containing MUC-1gp-positive PC, the infiltration of immunoglobulin (Ig) E PC and/or IgE-bound mast cells was significantly increased, but MUC-1gp-positive PC did not contain any specific immunoglobulin heavy or light chains. The findings suggest that the expression of MUC-1 gp in PC, although not restricted to IgE-class cells, may be induced in an allergic status. Plasma cells and PNC mainly reacted with the antibodies E29 and 115D8, while FDC and MFB were principally reactive with the antibody DF3. In some cases of multiple myeloma, the neoplastic PC were predominantly immunoreactive with DF3. The results indicate: (i) the epitopic variability of MUC-1gp molecules expressed on the non-epithelial cells; and (ii) the epitopic alterations during malignant transformation. It should also be noted that the expression of MUC-1gp in the non-epithelial cells represents a pitfall in histopathological diagnosis.

Cytokeratin positive T cell malignant lymphoma

A high grade T cell malignant lymphoma is described in which weak staining of tumour cells for leucocyte common antigen and T cell markers coexisted with strong positive cytoplasmic staining with the anticytokeratin marker CAM 5.2. This is the first report of non-CD30 positive T cell lymphoma showing cytokeratin positivity. On ultrastructural examination there was no evidence of epithelial differentiation or of accumulation of cytokeratin-type intermediate filaments. The case adds to the range of malignant lymphomas which can, on rare occasions, show cytokeratin positivity. Pathologists should be aware of this potential diagnostic pitfall if inappropriate investigations and therapeutic regimens are to be avoided.

Biclonal primary plasma cell leukemia

Authors present a multiparameter pathological study in a case of rapid biclonal primary plasma cell leukemia. The immunohistochemical data revealed aberrant phenotypes (monocyte, epithelial and T-cell) probably in connection with microenvironmental influences. Biclonality can be attributed to class switching during malignant transformation. Static image cytometry showed aneuploidy. The blasts of this process are active immunoregulatory cells.

Immunohistochemical markers in the diagnosis of neuroendocrine neoplasms of the head and neck

Immunohistochemistry is important in the diagnosis of neuroendocrine neoplasms of the head and neck, particularly in the differential diagnosis of the various neuroendocrine neoplasms, although the results of staining should never be interpreted alone, but together with conventional histopathologic findings. It is emphasized that there are currently no markers capable of distinguishing between benign and malignant tumors. A correct diagnosis is of paramount importance, since treatment depends on the diagnostic accuracy and prognosis is naturally related substantially to the phenotype.

Selection and characterization of an erythroeosinophilic subclone (LAMA-87) and an eosinophilic subclone (LAMA-88) from the multipotential cell line LAMA-84

The human leukemic cell line LAMA-84 was established and characterized as an erythromegakaryocytic cell line. In the present study we show that these cells can differentiate in estrone-treated athymic mice and give rise to an erythroeosinophilic cell line (LAMA-87). This new cell line expressed glycoporin A, alpha beta and gamma globin chain mRNA but also eosinophilic peroxidase. Hemin slightly increased the total hemoglobin production of the cells and phorbol diester (TPA), dimethyl sulfoxide (DMSO) and sodium butyrate (SB) increased the expression of megakaryocytic markers (gpIIb/IIIa complex). When inoculated into non-treated athymic mice, LAMA-87 cells can differentiate to give rise to eosinomonocytic cells (LAMA-88). This new cell line expresses eosinophilic peroxidase, Luxol fast blue stain and synthesizes lysozyme. Depending on the inducer used, LAMA-88 can differentiate along a monocytic lineage (TPA, DMSO, SB and vitamin D3). These three LAMA cell lines should be useful in further studies of the molecular regulation of the pluripotent cell commitment and may provide a model for the understanding of human hematopoiesis.

Different guises of plasmacytoma--from skin to bone

A case is reported of a patient with plasmacytoma which assumed different clinicopathological features over seven years. The tumour first presented as a subcutaneous mass which was misdiagnosed as anaplastic carcinoma. Complete response to radiotherapy ensued but recurrence took the form of an intracerebral tumour. Further complete response to "palliative" corticosteroids was followed by osseous lesions three years later, when the diagnosis of plasmacytoma was confirmed. This report illustrates the highly variable clinicopathological presentations of plasmacytoma, including the rare primary cutaneous manifestation.

Primary gastric CD30 (Ki-1)-positive large cell non-Hodgkin's lymphomas. A clinicopathologic analysis of six cases

BACKGROUND

The CD30/Ki-1 antigen characterizes a series of non-Hodgkin's lymphomas (NHL) predominantly showing anaplastic large cell (ALCL) morphology and frequently involving the skin and other extranodal sites. In cutaneous large cell lymphomas, the CD30 expression was indicated as a favorable prognostic marker independently from cytology, anaplastic versus nonanaplastic. The stomach is the most common site of extranodal lymphomas in the adult population, but primary gastric CD30+ lymphomas have been reported rarely.

METHODS

The clinical, morphologic, and immunohistochemical features of six cases with primary CD30/Ki-1+ gastric large cell lymphomas were analyzed.

RESULTS

The mean age of patients was 64 years with a prevalence of women (M:F ration = 1:2). Patients were assigned to Stage IE or IIE. Three of them died of disease, whereas the others are still alive (mean follow-up, 18 months). Three of six cases had ALCL morphology, whereas other cases had centroblastic, immunoblastic, and high-grade mucosa-associated lymphoid tissue lymphoma. Immunohistochemistry revealed a B-cell phenotype in three of six cases; a T-cell phenotype in one of six cases; and a null, non-B, non-T phenotype in two of six cases.

CONCLUSIONS

Within CD30+ primary gastric large cell lymphomas, cytology, anaplastic versus nonanaplastic, did not affect clinical presentation and/or prognosis. The survival rate of the patients studied is in keeping with literature reports regarding prognosis of primary high-grade gastric NHL. The findings suggest that clinical behavior of this extranodal lymphoma is more closely related to clinical symptoms and initial stage of disease than to CD30 expression.

CD30 (Ki-1)-positive, anaplastic large cell lymphoma mimicking gastrointestinal carcinoma

BACKGROUND

There is great diversity in the clinical presentation of CD30 (Ki-1)-positive, anaplastic large cell lymphoma (ALCL). The authors report two patients in whom the clinical and morphologic features mimicked gastrointestinal carcinoma.

METHODS

Surgical pathology specimens were examined using standard histologic techniques. Paraffin- and frozen-section immunohistochemistry was performed by an avidin-biotin-peroxidase method.

RESULTS

The first patient is a 58-year-old man who presented with a constricting mass of the sigmoid colon. Immunohistochemical staining for CD45 (LCA) was negative in formalin-fixed paraffin sections. However, CD45 and CD74 (LN2) were detectable in B5 postfixed material. The second patient is a 44-year-old woman who presented with dysphagia and back pain. Endoscopic examination revealed an ulcerated luminal mass in the proximal esophagus and a gastric ulcer. Mucosal biopsy specimens of the esophagus and stomach contained ALCL, which was CD45 positive. Retroperitoneal lymph nodes contained ALCL infiltrating the sinuses, interfollicular areas, and blood vessel lumina. In addition to CD45 and pan-T-cell antigens, the neoplastic cells expressed CD68 (KP1) and epithelial membrane antigen (EMA). Monoclonal antikeratins were negative, but a polyclonal antikeratin stain was positive.

CONCLUSIONS

These findings indicate that clinical, morphologic, and some immunologic features of ALCL may mimic gastrointestinal carcinoma.

Osteogenic sarcoma with epithelial differentiation

This case report details an osteogenic sarcoma arising in a vertebra in which cytokeratin intermediate filaments were detected immunohistochemically with three different antibodies. This feature was present not only in the primary neoplasm but also in two local recurrences and a metastasis to the iliac bone. What is unique about this primary bone tumor, however, is the structural evidence for epithelial differentiation. Ultrastructurally, well-formed desmosomes and tonofilaments were present in all four surgically resected specimens. This tumor expands the list of soft tissue and bone tumors in which anomalous expression of intermediate filaments can occur but, more important, illustrates that changes in genetic expression of neoplasia of mesenchymal origin can result in paradoxic epithelial differentiation.

Frequent expression of haemopoietic and non-haemopoietic antigens by neoplastic plasma cells: an immunohistochemical study using formalin-fixed, paraffin-embedded tissue

There is increasing evidence that neoplastic plasma cells express various haemopoietic and non-haemopoietic antigens. Since this issue could raise problems in diagnostic histopathology, we have investigated 51 cases of multiple myeloma (plasmacytoma) systematically with a broad panel of antibodies applicable on paraffin-embedded and mildly decalcified tissue. In approximately 90% of the cases the neoplastic plasma cells reacted with at least one antibody detecting haemopoietic antigens: MB2 (75%), DF-T1/CD 43 (59%), UCHL1/CD 45RO (47%), Ki-B3 (41%), anti-LCA/CD 45 (40%), L26/CD 20 (26%), 4KB5/CD 45RA (18%), Ber H2/CD 30 (10%), anti-neutrophil elastase (4%), anti-Leu-7/CD 57 (8%), Dako-M1/CD 15 (2%), KP1/CD 68 (2%) and anti-glycoprotein IIIa (2%). In approximately 70% of the cases the cells reacted with antibodies against non-haemopoietic antigens: anti-epithelial membrane antigen (65%), BMA120 (53%), anti-vimentin (44%), anti-pan-cytokeratin/KL1 (8%), anti-carcino-embryonic antigen (6%) and HMB45 (6%). Lack of awareness of the frequent expression of both haemopoietic and non-haemopoietic antigens by neoplastic plasma cells could lead to mis-diagnosis of plasmacytomas as malignant lymphomas or even as carcinomas or sarcomas.

Cytokeratin-immunoreactive cells of human lymph nodes and spleen in normal and pathological conditions. An immunocytochemical study

The occurrence and the distribution of cytokeratin (CK)-immunoreactive reticulum cells in a series of normal and pathological human lymph nodes and spleens are documented. The immunoreactive cells exhibit morphological and immunophenotypic features of so-called fibroblastic reticulum cells, with or without myoid differentiation. They invariably co-express vimentin and, to a lesser extent, desmin and muscle-specific actin isoforms. These CK-immunoreactive cells are apparently a normal subpopulation of reticulum cells, being detectable from the early stages of spleen and lymph node development. They are distributed mainly in the paracortical and medullary regions of the lymph nodes and at the periphery of the white pulp in the spleen. Their number and distribution are highly variable in different neoplastic and non-neoplastic pathological conditions but the changes are not disease specific. CK-immunoreactive reticulum cells are easily identifiable in both frozen and fixed lymphoid tissue and in cytological smears of fine-needle aspirates, provided that monoclonal antibodies whose spectrum of reactivity includes cytokeratins 8 and 18 are used. The awareness of the occurrence of CK-immunoreactive cells in normal lymphoid tissues is of particular relevance in the search for micrometastatic foci using anti-CK antibodies.

Interleukin-2 receptor antigen, leukocyte common antigen, and Ki-1 antigen-expressing gastric plasmacytoma. A case report with an immunohistochemical study

A case of primary gastric plasmacytoma expressing various surface and cytoplasmic antigens is reported. With the use of formalin-fixed and deparaffinized sections, 13 different antibodies were applied. Neoplastic plasma cells revealed monoclonal IgG and kappa light chain in the cytoplasm, and expressed epithelial membrane antigen, Ki 67 antigen, cytokeratin, CD 22 antigen, interleukin-2 receptor antigen, leukocyte common antigen and Ki-1 (CD 30) antigen. However, tumor cells were devoid of HLA-DR antigen. These data suggest that the neoplastic plasma cells are at the plasmoblastic stage of maturation and express various surface and cytoplasmic phenotypes.

K562 erythroleukemia cells express cytokeratins 8, 18, and 19 and epithelial membrane antigen that disappear after induced differentiation

The effects of differentiation-modulating drugs were studied on the expression of intermediate filaments (IFs) in the human K562 erythroleukemic cell line. The untreated cells contained typical cytoplasmic coiling bundles, positive for both vimentin and cytokeratin as judged by indirect immunofluorescence microscopy with monoclonal antibodies (Mabs). Some of the cells also showed bright immunoreactivity for epithelial membrane antigen (EMA), as revealed with a Mab and polyclonal antiserum. When exposed to hemin or to sodium butyrate, most of the cells became cytokeratin negative within 3 days and showed dispersion of vimentin fibrils. Upon exposure to the phorbol ester 12-O-tetradecanoylphorbol-13-acetate (TPA), the amount of both vimentin and cytokeratin appeared to be greatly increased within 3 days and was found both in dispersed cytoplasmic fibrils, in large spherical, eccentric aggregates, as well as in cytoplasmic fibrils in cells spreading on fibronectin. TPA induced a complete loss of proliferation, as judged by immunostaining with the Mab Ki-67. The effects of TPA were found to be irreversible and could be induced by only a short exposure to the drug. Western blotting analysis and monoclonal antibodies to individual cytokeratins revealed that untreated K562 cells expressed Mr 52,000 (No. 8), 46,000 (No. 18), and 40,000 (No. 19) cytokeratin polypeptides, which disappeared when the cells were exposed to hemin or to sodium butyrate to induce erythroid differentiation but were greatly enhanced when exposed to TPA. The monoclonal anti EMA antibody reacted in K562 cells with a single Mr 320,000 polypeptide that was also revealed in MCF-7 breast carcinoma cells. Human bone marrow cells or other leukemic cell lines with erythroid differentiation capacity (HEL and KG-1) did not contain cytokeratin- or EMA-immunoreactive cells, suggesting that in K562 cells these properties may rather represent abnormal cytodifferentiation or retrodifferentiation toward early embryonic mesenchymal cells, than a more general expression of epithelial features in human leukemic cells.

Cytokeratin expression in chondroblastomas

The present study is based on the histopathological and immunohistochemical examination of seven chondroblastomas, including one lung metastasis occurring 9 years after treatment. Chondroblastomas were shown to co-express vimentin, S-100 protein, neuron-specific enolase, and the epithelial markers recognized by CAM 5.2, EMA and a polyclonal cytokeratin antibody. The cytokeratins present in the tumour cells of the lung metastasis were characterized as cytokeratins 8, 18, 19 and, to a lesser extent, cytokeratin 7. The results suggest aberrant cytokeratin expression in chrondroblastomas.

Cytokeratins and cytokeratin filaments in subpopulations of cultured human and rodent cells of nonepithelial origin: modes and patterns of formation

Using immunofluorescence microscopy, we observed that in several established cell culture lines derived from different nonepithelial tissues and species, cells spontaneously emerge, usually at low frequencies, which contain cytoplasmic structures decorated by antibodies specific for cytokeratins 8 and 18. This phenomenon was further examined at both the protein (gel electrophoreses of cytoskeletal proteins, followed by immunoblotting) and the RNA (Northern blots, "nuclear run-on" analysis, in situ hybridization) level. Positive cell lines included simian virus (SV40)-transformed human fibroblasts (HF-SV80, WI-38 VA13), human astrocytic glioma cells (U333 CG/343MG), rat (RVF-SMC) and hamster (BHK-21/13) cells derived from vascular smooth muscle and murine sarcoma MS-180 cells. In two cell lines (HF-SV80 and BHK-21/13), the frequency of the cytokeratin-containing cells and of the cytokeratin fibril arrays per cell was drastically increased upon treatment with 5-azacytidine. The structural appearance of the cytokeratins was variable in the different cell lines but could also differ among cells of the same culture: While small granular or comma-shaped structures or bizarrely shaped filament arrays prevailed in WI-38, RVF and normally grown BHK-21 cells, most of the other lines revealed extended normal-looking, fibrillar arrays. In one line (MS-180), the appearance of cytokeratins was associated with a morphological change, as it was only found in a subpopulation of cells that had lost their typical elongated and spindle-shaped phenotype and assumed a rounded ("coccoid") shape. Our results show that the expression of the genes encoding cytokeratins 8 and 18 is not necessarily restricted to programs of epithelial differentiation and that factors stochastically effective appear in cultured cell lines that allow the synthesis of these cytoskeletal components. Mechanisms possibly involved in this spontaneous and selective advent of cytokeratins 8 and 18 and implications for tumor diagnosis are discussed.

Lymphoma phenotyping in formalin-fixed and paraffin wax-embedded tissues: II. Profiles of reactivity in the various tumour types

Recently, monoclonal antibodies capable of phenotyping malignant lymphomas in routinely fixed and processed tissue have become available. Some of these reagents identify lineage-restricted variants of the leucocyte common molecule, whereas others identify unique fixation-resistant epitopes on lymphoid cells, some of which are shared by non-lymphoid tissues. A new generation of antibodies recognizing 'classical' leucocyte antigens such as CD3 are also emerging. Refinements in antigen detection systems, especially for immunoglobulin recognition, combined with these new reagents promise to improve the accuracy of lymphoma diagnosis in routine histopathology. These new antibodies are reviewed, and their limitations, cross reactivities and profiles of staining in lymphoreticular disease are discussed. A strategy for their optimal use is proposed.