Diagnostic immunohistochemistry of canine round cell tumors

Review of diagnostic histologic features of cutaneous round cell neoplasms in dogs

Cutaneous round cell neoplasms (RCNs) are among the most common skin tumors of dogs. Although a diagnosis can be made in most cases following the examination of H&E-stained routine samples, less-differentiated neoplasms can exhibit overlapping morphologic features that may be challenging to the pathologist, and require immunohistochemistry or molecular testing to reach a final diagnosis. Many patients with cutaneous RCNs are initially seen by a general practitioner and are not referred to a veterinary teaching hospital until a diagnosis has been made. For this reason, anatomic pathology residents at some academic or other training institutions may not be exposed frequently to RCNs during the surgical biopsy service as part of their residency training. In an attempt to fill that gap, here we review the key routine histologic features of canine cutaneous RCNs.

Immunohistochemical Labeling of Multiple Myeloma Oncogene 1/Interferon Regulatory Factor 4 (MUM1/IRF-4) in Canine Cutaneous Histiocytoma

Multiple myeloma oncogene 1/interferon regulatory factor 4 (MUM1/IRF-4) immunohistochemistry (IHC) is mainly used for diagnostic confirmation of plasma cell tumors (PCTs) in dogs and cats. This article describes MUM1/IRF-4 IHC expression in 20 cases of canine cutaneous histiocytoma (CH) and compares it with 10 cutaneous or mucocutaneous PCTs and 5 cutaneous histiocytic sarcomas (HSs) submitted to the same IHC protocol. All histiocytomas had strong nuclear and variable cytoplasmic immunolabeling for MUM1/IRF-4, whereas all PCTs had strong nuclear and moderate cytoplasmic immunolabeling for MUM1/IRF-4. No MUM1/IRF-4 immunolabeling was detected in the HSs. Although not typically a diagnostic challenge, MUM1/IRF-4 expression may have to be used with caution or in conjunction with additional immunomarkers to differentiate among poorly differentiated round cell tumors, especially when a histiocytic or plasma cell origin is suspected.

Immunohistochemical, lectin histochemical and ultrastructural studies of canine transmissible venereal tumor in Brazil

ABSTRACT: Canine transmissible venereal tumor (CTVT) is a naturally occurring contagious round-cell neoplasia, with poorly understood origin and transmission. This study aims to further investigate the tumor nature through immunohistochemistry, lectin histochemistry and transmission electron microscopy (TEM) analysis, and to provide support for diagnostic and differential diagnoses of CTVT. Immunohistochemistry was performed in 10 genital and six exclusively extragenital tumors, which were previously diagnosed by citology and histopathology. CTVT samples were incubated with biotinylated antibodies to specific membrane and cytoplasmic antigens (anti-lysozyme, anti-macrophage, anti-vimentin, anti-CD18, monoclonal anti-CD117, monoclonal anti-CD3, polyclonal anti-CD117, polyclonal CD3 and anti-CD79a), followed by the avidin-biotin-peroxidase complex technique. The lectins Con A, DBA, SBA, PNA, UEA-1, WGA, sWGA, GSL, JSA, PSA, PHA-L, PHA-E and RCA were additionally tested in four genital CTVTs and TEM was performed in eight genital tumors. The anti-vimentin antibody revealed strong immunoreactivity to neoplastic cells in all the assessed samples (16/16). The polyclonal anti-CD3 antibodies showed moderate to strong immunoreactivity in fourteen (14/16) and the polyclonal anti-CD117 in fifteen cases (15/16). There was no immunoreactivity to anti-lysozyme, anti-macrophage, anti-CD18, monoclonal anti-CD117, monoclonal anti-CD3 and anti-CD79a antibodies. At lectin histochemistry, it was observed strong staining of tumor cells to Con-A, PHA-L and RCA. There was no histopathological and immunoreactivity differences between genital and extragenital CTVTs. These findings do not support the hypothesis of histiocytic origin of CTVT. In contrast, the lectin histochemical results were similar to cells from lymphoid/myeloid origin.

Immunocytochemical characterization of primary cell culture in canine transmissible venereal tumor

Abstract: Immunochemistry with anti-vimentin, anti-lysozyme, anti-alpha 1 antitrypsin, anti-CD3 and anti-CD79α antibodies has been used for characterization of primary cell culture in the transmissible venereal tumor (TVT). Samples for primary cell culture and immunohistochemistry assays were taken from eight dogs with cytological and clinical diagnosis of TVT. To validate the immunochemical results in the primary cell culture of TVT, a chromosome count was performed. For the statistical analysis, the Mann-Whitney test with p<0.05 was used. TVT tissues and culture cells showed intense anti-vimentin immunoreactivity, lightly to moderate immunoreactivity for anti-lysozyme, and mild for anti-alpha-antitrypsin. No marking was achieved for CD3 and CD79α. All culture cells showed chromosomes variable number of 56 to 68. This is the first report on the use of immunocytochemical characterization in cell culture of TVT. Significant statistic difference between immunochemistry in tissue and culture cell was not established, what suggests that the use of this technique may provide greater certainty for the confirmation of tumors in the primary culture. This fact is particularly important because in vitro culture of tumor tissues has been increasingly used to provide quick access to drug efficacy and presents relevant information to identify potential response to anticancer medicine; so it is possible to understand the behavior of the tumor.

Comparative Aspects of Canine Melanoma

Melanomas are malignant neoplasms originating from melanocytes. They occur in most animal species, but the dog is considered the best animal model for the disease. Melanomas in dogs are most frequently found in the buccal cavity, but the skin, eyes, and digits are other common locations for these neoplasms. The aim of this review is to report etiological, epidemiological, pathological, and molecular aspects of melanomas in dogs. Furthermore, the particular biological behaviors of these tumors in the different body locations are shown. Insights into the therapeutic approaches are described. Surgery, chemotherapy, radiotherapy, immunotherapy, and the outcomes after these treatments are presented. New therapeutic perspectives are also depicted. All efforts are geared toward better characterization and control of malignant melanomas in dogs, for the benefit of these companion animals, and also in an attempt to benefit the treatment of human melanomas.

Transmissible Tumors: Breaking the Cancer Paradigm

Transmissible tumors are those that have transcended the bounds of their incipient hosts by evolving the ability to infect another individual through direct transfer of cancer cells, thus becoming parasitic cancer clones. Coitus, biting, and scratching are transfer mechanisms for the two primary species studied, the domestic dog (Canis lupus familiaris) and the Tasmanian devil (Sarcophilus harrisii). Canine transmissible venereal tumors (CTVT) are likely thousands of years old, and have successfully travelled from host to host around the world, while the Tasmanian devil facial tumor disease (DFTD) is much younger and geographically localized. The dog tumor is not necessarily lethal, while the devil tumor has driven the population to near extinction. Transmissible tumors are uniform in that they have complex immunologic profiles, which allow them to escape immune detection by their hosts, sometimes for long periods of time. In this review, we explore how transmissible tumors in CTVT, DFTD, and as well as the soft-shell clam and Syrian hamster, can advance studies of tumor biology.

Immunohistochemical study of genital and extragenital forms of canine transmissible venereal tumor in Brazil

Aiming to provide insight and discussing the problems related to the diagnosis and differential diagnosis of canine transmissible venereal tumor (CTVT), especially in its extragenital form, immunohistochemical evaluation was performed and a comparison was established by analysis of the microscopic appearance of 10 genital CTVTs and 13 exclusively extragenital CTVTs previously diagnosed by cytology and histopathology. CTVTs samples were incubated with biotinylated antibodies raised against specific membrane (anti-macrophage) and cytoplasmic antigens (anti-lysozyme, anti-S-100 protein, anti-vimentin and anti-CD18) and subsequently developed using streptavidin-biotin peroxidase and streptavidin-biotin-alkaline phosphatase methods. A strong reactivity with the anti-vimentin antibody was found in 100% of the tumors tested (22/22). No reactivity was found for the anti-lysozyme, anti-macrophage, anti-S-100 protein and anti-CD18. No histopathological or immunoreactivity differences between genital and extragenital CTVTs were found. These findings do not corroborate the hypothesis of histiocytic origin of CTVT (no reactivity to anti-lysozyme, anti-macrophage and anti-CD 18 antibodies). In addition, the antibody panel used is useful to narrow the differential diagnosis for lymphomas, histiocytic tumors, amelanotic melanomas, and poorly differentiated epithelial neoplasias, among others.

Immunohistochemical study of expression of immunoglobulins in canine B-cell lymphomas

Nineteen canine lymphomas were included in this study. Tumors were classified according to the updated Kiel classification adapted for canine lymphomas by Fournel-Fleury et al. Immunoglobulin light chains (κ and λ) and IgM and IgG expression were determined by immunohistochemical method. In all examined cases neoplastic cells were positive for one of the immunoglobulin light chains. Expression of λ light chains and κ light chains was observed in 18/19 and 1/19 tumors, respectively. In the majority of neoplastic cells in each examined specimen this reaction had a membranous pattern (sκ/sλ). In all examined cases the presence of immunoglobulin light chains was also observed in the cytoplasm of some neoplastic cells (cκ/cλ). These cells were usally rare and never constituted a dominant population. The expression of immunoglobulin was found in 13/19 cases. Most lymphomas were sIgM positive (11/13 cases). In one case expression of IgG was found, and in another lymphoma two populations of neoplastic cells with different expression of examined immunoglobulins (cells with IgM+and IgG+phenotypes) were observed. The reaction also had a membranous pattern. The cells containing cytoplasmic immunoglobulins were rare, and in most cases were of the same type as the surface immunoglobulins. Our study has confirmed that canine lymphomas are a monoclonal proliferation of B-cells usually expressing immunoglobulin λ light chains and that the vast majority of tumors deriving from B-cells express IgM. Our study also indicates a possibility of occurence of biclonal lymphomas in canine species.

Clonally transmissible cancers in dogs and Tasmanian devils

Tasmanian devil facial tumor disease (DFTD) and canine transmissible venereal tumor (CTVT) are the only known naturally occurring clonally transmissible cancers. These cancers are transmitted by the physical transfer of viable tumor cells that can be transplanted across histocompatibility barriers into unrelated hosts. Despite their common etiology, DFTD and CTVT have evolved independently and have unique life histories and host adaptations. DFTD is a recently emerged aggressive facial tumor that is threatening the Tasmanian devil with extinction. CTVT is a sexually transmitted tumor of dogs that has a worldwide distribution and that probably arose thousands of years ago. By contrasting the biology, molecular genetics and immunology of these two unusual cancers, I highlight the common and unique features of clonally transmissible cancers, and discuss the implications of clonally transmissible cancers for host-pathogen evolution.

Canine vascular neoplasia--histologic classification and inmunohistochemical analysis of 221 tumours and tumour-like lesions

A light microscopic evaluation of 221 canine vascular tumours and tumour-like lesions, supplemented by immunohistochemistry (von Willebrand Factor, CD31, vimentin), revealed a high degree of conformity with similar conditions in humans. Four main categories of tumours are reported, i.e. benign types: haemangiomas (n=127) and lymphangioma (n=1); tumour-like lesions: papillary endothelial hyperplasia (n=8) and vascular ectasias (n=2); neoplasms of intermediate malignancy: haemangioendotheliomas (n=27), and the obvious malignant form: angiosarcomas (n=57). Further classification showed that all subtypes had their human counterparts. Papillary endothelial hyperplasia and arteriovenous and venous haemangiomas are described for the first time in dogs. The combination of conventional histopathologic methods and immunohistochemistry was in many cases very useful diagnostically, the latter technique being in some cases indispensable for establishing a definite diagnosis. In general CD31 was the most useful marker for tumours originating from endothelial cells, especially for poorly differentiated haemangiosarcomas.

Ferret oncology: diseases, diagnostics, and therapeutics

Many standard diagnostic and chemotherapeutic protocols can be adapted for use in ferrets. Unique anatomic and clinical features dictate modification of protocols, but should not prohibit diagnosis or treatment. Ferrets may be the easiest of nontraditional species to treat with chemotherapeutics. We can provide more options for our patients, with improved quality of life and longer survival times than ever before. Although clients are never happy to hear the diagnosis of "cancer," it is no longer a word that condemns their beloved pet.

Canine transmissible venereal tumour: Cytogenetic origin, immunophenotype, and immunobiology. A review

Canine transmissible venereal tumour (CTVT) is the only known naturally occurring tumour that can be transplanted as an allograft across major histocompatibility (MHC) barriers within the same species, and even to other members of the canine family, such as foxes, coyotes and wolves. The progression of this tumour is unique in that, it follows a predictable growth pattern. In natural and experimental cases, the growth pattern includes progressive growth phase, static phase and regression phase, and this is followed by transplantation immunity in immunocompetent adults, while metastasis occurs in puppies and immunosuppressed dogs. Because of the uniqueness of CTVT transmission and progression, experimental investigations of various aspects of the biology of CTVT have been used to provide clues to the immunobiology of both animal and human tumours. This review examines the current state of knowledge of the aspects of the cytogenetic origin, immunophenotype, immunobiology and immunotherapy of CTVT.

Histopathologic and immunophenotypic characterization of extramedullary plasmacytomas in nine cats

To contribute to the existing body of knowledge in the literature on the apparently rare extramedullary plasmacytoma in cats, lymphoid tumors with plasmacytic cellular morphology taken from nine cats were examined. The paraffin-embedded material was investigated by standard hematoxylin and eosin, and special staining techniques (Giemsa, Congo-red, and periodic acid-Schiff reaction). The tumors also were examined immunohistochemically for the presence of immunoglobulin G, immunoglobulin A, immunoglobulin M, immunoglobulin light chains (lambda, kappa), various amyloid proteins, and FeLV-antigen (p27 protein). An immunoglobulin-producing tumor of plasmacellular origin (extramedullary plasmacytoma [EMP]) could be diagnosed in all cases on the basis of immunohistochemical light-chain expression. All but one of the neoplasms occurred in the skin of older, predominantly male cats. As in humans and dogs, the following types could be identified according to their morphologic features: mature type (two), cleaved type (two), asynchronous type (four), and polymorphous type (one). The tumor tissue of three cats revealed amyloid deposits, which were immunohistochemically diagnosed as ALlambda-amyloid in all three cases.

Immunophenotyping lymphomas in dogs: a comparison of results from fine needle aspirate and needle biopsy samples

The reliability of utilizing cytologic samples for immunophenotyping canine lymphomas was evaluated by a systematic comparison of results from fine needle aspirate (FNA) to needle biopsy specimens stained by immunochemical methods. The specific reactivity of a selected panel of 12 antibodies to cell surface markers and intermediate filaments was assessed in 11 dogs by comparing cytologic to histologic samples. There was excellent correlation of results between immunostained cytologic and histologic samples. FNA sampling is a simple, noninvasive method for determining the lymphoid phenotype in canine lymphoma. In addition, this technique may be useful as a cytodiagnostic aid in differentiating lymphoid from non-lymphoid tumors and in assessing neoplastic vs. reactive or hyperplastic processes.

A comparative review of melanocytic neoplasms

Melanoma is a devastating disease frequently encountered within both veterinary and human medicine. Molecular changes linked with neoplastic transformation of melanocytes include mutations in genes that encode proteins intrinsic to the regulatory pathways of two tumor suppressor proteins (retinoblastoma protein and p53), proto-oncogene mutation to oncogenes, altered expression of epithelial cadherin and CD44 adhesion molecules, and upregulation of angiogenic factors and other growth factors. Histologic evaluation of the primary mass is the most common means of diagnosis, with cytology used more frequently to document metastasis. Melanoma's highly variable histologic and cytologic patterns can make diagnosis by either method problematic. Adherent epithelioid morphology, including signet ring forms, and nonadherent round and spindle forms are recognized, with pigmentation an inconsistent finding. The site of the tumor, the thickness of the primary tumor or depth of invasion, and the number of mitotic figures per high-power field or per millimeter are used histologically to predict biologic behavior, whereas site and degree of pleomorphism are typically used for cytologic preparations. Diagnosis of amelanotic melanoma can be aided by ancillary diagnostic techniques. Tumor cells are usually positive for vimentin, S100, neuron-specific enolase, and Melan-A, and negative for cytokeratin. Melan-A as a positive marker is not as sensitive as the others are but is likely more specific. Monoclonal antibodies to human melanosome-specific antigens 1 and 5 cross-react with canine antigens for a combined sensitivity rate of 83%. Mouse monoclonal antibody IBF9 specifically recognizes canine melanoma antigen and also has good sensitivity. Serologic markers, including cytokines, cell adhesion molecules, and melanoma-inhibitory activity, are being investigated as potential sentinels of melanoma. Currently, there is no single diagnostic technique capable of differentiating benign from malignant melanocytic neoplasms or predicting survival time.

Use of immunocytochemical techniques in canine melanoma

The staining patterns of the monoclonal antibodies S-100 and Melan-A in canine melanoma were assessed based on cytological specimens of six canine melanomas (four benign, two malignant). In addition, eight regional lymph nodes of the two dogs with malignant melanomas were stained using these markers. For reference, all specimens were also evaluated immunohistochemically using S-100 and Melan-A. To assess the immunocytochemical specificity of both antibodies, various canine tumours and normal tissues were stained. The immunocytochemical staining results of the canine melanomas and the regional lymph nodes showed high conformity with the immunohistochemical reactivity patterns for S-100 and Melan-A. The specificity of Melan-A was higher compared with S-100. Melan-A, in particular, may be helpful for the cytological diagnosis of canine melanoma.

Expression of S100a, vimentin, NSE, and melan A/MART-1 in seven canine melanoma cells lines and twenty-nine retrospective cases of canine melanoma

We evaluated the expression of vimentin, S100a, and Melan A/MART-1 (melanoma antigen recognized by T cells 1) in seven cell lines established independently from dogs with canine melanoma. We also compared routine immunostaining of 29 clinical specimens from melanoma cases using vimentin, S100a, and neuron-specific enolase (NSE) with staining for Melan A/MART-1 as part of a diagnostic panel. All the cell lines were positive for expression of vimentin and S-100a. MelanA/MART-1 expression was seen consistently in only two of the seven cell lines. Staining for Melan A/MART-1 was most intense near areas of heavy melanin pigmentation. All except one of the clinical specimens were positive for vimentin. S 100a was expressed in the majority of both pigmented (15/20, 75%) and amelanotic (8/9, 88.8%) tumors. Seventeen of 29 (58.6%) tumors were positive for NSE. Melan A/MART-1 was expressed in 18/29 (62%) tumors, including 90% of pigmented tumors, but in no amelanotic tumors. Intensity of Melan A/MART-1 staining correlated positively with biologic behavior, with seven malignant tumors showing negative to weak staining and 10 benign tumors showing moderate to strong staining. Three malignant tumors showed moderate to intense staining for Melan A/ MART-1. Our results suggest that expression of Melan A/MART-1 may be unstable in cultured cell lines. Assessment of both S100a and Melan A/MART-1 expression is useful to confirm a diagnosis of canine melanoma, and Melan A/MART-1 may be especially informative regarding the biologic behavior of these tumors.

Use of a murine xenograft model for canine transmissible venereal tumor

OBJECTIVE

To develop a murine model for canine transmissible venereal tumor (CTVT).

ANIMALS

Thirty-three 6-week-old NOD/LtSz-scid (NOD/SCID) mice and seven 6-week-old C57BL/6J mice.

PROCEDURE

Samples of CTVT were excised from a 3-year-old dog and inoculated SC into ten 6-week-old NOD/SCID mice to induce growth of xenograft transmissible venereal tumor (XTVT). To establish mouse-to-mouse transmission, samples of XTVT were removed and inoculated SC into 4 groups of 6-week-old NOD/SCID mice and into a control group. Samples of CTVT were also inoculated into immunocompetent C57BL/6J mice for a mouse antibody production (MAP) test. The canine and xenografted tumors were evaluated cytologically and histologically, and polymerase chain reaction was performed for detection of the rearranged LINE/c-MYC junction.

RESULTS

8 of 10 NOD/SCID mice that were inoculated with CTVT developed tumors 3 to 10 weeks after inoculation. In the second-generation xenograft, all mice developed tumors by postinoculation day 47; 1 X 10(6) of XTVT cells were enough to create a xenograft. Metastases developed in 4 of 20 mice. Xenografted and metastatic tumors retained cytologic, histologic, and molecular characteristics of CTVT. Results of the MAP test were negative for all pathogens.

CONCLUSION

We established an NOD/SCID murine model for XTVT and metastasis of CTVT. This model should facilitate study of tumor transplantation, progression, and metastasis and should decrease or eliminate the need for maintaining allogenic transfer in dogs.

Retrospective study of 338 canine oral melanomas with clinical, histologic, and immunohistochemical review of 129 cases

Diagnostic records from 338 canine oral melanomas in 338 dogs received at the Veterinary Medical Diagnostic Laboratory (1992-1999) were reviewed. Of these tumors, 122 plus an additional 7 metastatic melanomas of unknown origin were selected for clinical follow-up, histologic review, and immunohistochemistry. Chow Chow, Golden Retriever, and Pekingese/Poodle mix breeds were overrepresented, whereas Boxer and German Shepherd breeds were underrepresented. There was no gender predisposition and the average age at presentation was 11.4 years. Forty-nine dogs were euthanized due to recurrence or metastasis. The average postsurgical survival time was 173 days. The gingiva and the labial mucosa were the most common sites. Most tumors were composed of either polygonal cells (27 cases, 20.9%), spindle cells (44 cases, 34.1%), or a mixture of the two (polygonal and spindle) (54 cases, 41.9%). Clear cell (3 cases, 2.3%) and adenoid/papillary (1 case, 0.8%) patterns were uncommon. The metastases of 6/6 oral melanomas had morphologic and immunohistochemical features similar to those of the primary tumors. Immunohistochemically, Melan A was detected in 113/122 oral (92.6%) and 5/7 (71.9%) metastatic melanomas. Only 4/163 nonmelanocytic tumors were focally and weakly positive for Melan A. Antibodies against vimentin, S100 protein, and neuron-specific enolase stained 129 (100%), 98 (76%), and 115 (89.1%) of 129 melanomas, respectively. Antibodies against other melanocytic-associated antigens (tyrosinase, glycoprotein 100) did not yield adequate staining. We conclude that Melan A is a specific and sensitive marker for canine melanomas.

Immunohistochemical characterization of hepatic lesions associated with Elaeophora elaphi parasitism in red deer (Cervus elaphus)

This study was based on the immunohistochemical characterization of hepatic lesions caused by Elaeophora elaphi in 15 red deer. In eight animals filariae were found in branches of the portal vein. "Web-like" endophlebitis (15 cases), lymph nodule-like thrombi associated with filarial debris (12 cases) and fibrinous thrombi (three cases) were also observed in the portal vein. Multifocal granulomatous hepatitis (six cases) and lymph nodule-like tissue (three cases) were found in the liver parenchyma. The distribution of CD3 antigen, IgG-lambda light chains, and S-100 protein in lymphoid tissue in the portal vein thrombi and hepatic parenchyma was similar to that found in the cortex of the lymph nodes. In these lesions, lymphoid follicles with large germinal centres (mainly composed of IgG+ B lymphocytes, with occasional S-100+ follicular dendritic cells) predominated over interfollicular lymphoid tissue (mainly composed of CD3+ T lymphocytes and S-100+ interdigitating cells). This suggested that the local humoral immune response was more important than the cellular response in this parasitic disease. The presence of interdigitating and follicular dendritic cells confirmed the high degree of organization of the abnormal lymphoid tissue and suggested that antigen presentation to T and B lymphocytes and the subsequent proliferation of the latter was particularly efficient in such tissue. The latter may therefore be superior to diffuse granulomatous infiltrate in terms of the production of a local immune response.

Expression of major histocompatibility complex class II antigen in neoplastic cells of canine cutaneous histiocytoma

Forty five cases of canine cutaneous histiocytoma (CCH) were examined by immunohistology for expression and distribution of major histocompatibility complex (MHC) class II antigen in neoplastic cells. In addition, expression of lysozyme and calprotectin (leucocyte protein L1) in neoplastic cells was investigated. Furthermore, B and T lymphocytes were demonstrated by antibodies against the CD3 antigen, IgG, and IgM. Neoplastic cells showed two staining patterns for MHC class II antigen: focal juxtanuclear cytoplasmic staining and/or rim-like staining along the cell periphery. In 24 cases, a predominant or exclusive focal juxtanuclear cytoplasmic MHC class II antigen reaction in neoplastic cells, and the presence of few diffusely distributed infiltrating CD3 antigen-positive T lymphocytes were observed. Tumors with numerous neoplastic cells exhibiting staining for MHC class II antigen along the cell periphery (n = 21) showed increased inflammatory alterations, represented by disseminated and nodular infiltrations of mainly CD3 antigen-positive T cells. B cells, plasma cells, exudate macrophages, and neutrophils were rarely seen disseminated between neoplastic cells whereas their number increased within focal inflammatory infiltrates. The focal cytoplasmic reaction for MHC class II antigen in neoplastic cells might represent newly synthesized MHC class II molecules stored in vesicles, whereas staining of the cell periphery might occur due to accumulation of MHC class II molecules along the plasma membrane. The increasing expression of MHC class II molecules on the cell surface might be the decisive factor for onset and progression of tumor regression. However, the exact mechanism of priming and activation of T cells by neoplastic cells and the nature of the presented antigen are not yet known.

S-100 immunoreactivity in melanomas of two marsupials, a bird, and a reptile

S-100 proteins are abundant in melanocytes of the skin; thus, S-100 immunoreactivity has been used as a diagnostic criterion for melanoma in humans and other placental mammals. We tested cutaneous melanomas of two marsupials, a bird, and a snake for S-100 immunoreactivity, using a polyclonal rabbit antibovine S-100 antibody. The tumor from a Tasmanian Pademelon (Thylogale billaridierii) was composed of large epithelioid cells, most of which had S-100-positive cytoplasm. In general, there were only scattered individual spindle-shaped S-100-positive cells or groups of cells in the primary mass from a Spotted-tailed Quoll (Dasyurus maculatus); S-100 staining was primarily nuclear. Cells comprising the melanomas of the Australian Cormorant (Phalacrocorax carbo) and the Death Adder (Acanthophis antarcticus) were S-100-negative, although peripheral nerve bundles in both were S-100-positive.

Radiofrequency catheter ablation of the atria eliminates pacing-induced sustained atrial fibrillation and reduces connexin 43 in dogs

BACKGROUND

We assessed the effects of radiofrequency catheter ablation (RFCA) of the atrial epicardium on pacing-induced sustained atrial fibrillation (AF) and the expression and distribution of the intercellular gap junction protein connexin 43 (Cx43) in dogs.

METHODS AND RESULTS

In 12 mongrel dogs, after creation of complete AV block and implantation of a ventricular inhibited pacemaker, a high-rate pulse generator (20 to 30 Hz to induce AF) was implanted in the neck, connected to a right atrial endocardial pacing lead, and used to pace the atrium for 10 to 14 weeks. In group 1 (n=9 dogs), corrected sinus node recovery time (CSNRT), P-wave duration, 24-hour Holter ECG, maximal heart rate (MHR) in response to isoproterenol, and intrinsic heart rate (IHR) after atropine (0.04 mg/kg) and propranolol were measured before and after atrial pacing and RFCA. Group 2 dogs were used to assess the effect of chronic AF alone on Cx43 expression and distribution. All group 1 dogs developed sustained (>24 hours) AF. Right-sided RFCA of the atria eliminated the sustained AF in 5 dogs, but both right and left atrial RFCA was required to abolish sustained AF in the other 4 dogs. After RFCA restored sinus rhythm, CSNRT and P-wave duration were prolonged and MHR and IHR were decreased. Chronic rapid atrial pacing (group 2) increased the expression of Cx43, which was absent in ablated areas and markedly depressed in viable atrial myocytes near the ablation zones (group 1).

CONCLUSIONS

Rapid atrial pacing for long time periods induced sustained AF that can be eliminated by linear right and left atrial lesions created with RFCA, with preservation of sinus rhythm and atrial contractile function. Chronic AF increased the expression and distribution of gap junction protein Cx43, which became reduced in ablated and nearby nonablated areas.

S-100 immunoreactivity in melanomas of the South American opossum Monodelphis domestica

S-100 immunoreactivity was determined 1) in foci of melanocytic hyperplasia, 2) in naturally occurring, ultraviolet radiation-induced, and 9,10-dimethyl-1,2-benzanthracene (DMBA)-induced primary melanomas, and 3) in metastatic melanoma lesions in the South American opossum Monodelphis domestica. Preneoplastic lesions of melanocytic hyperplasia contained scattered cells with S-100-positive nuclei. All primary melanomas, with the exception of a single DMBA-induced tumor, contained cells with S-100-positive nuclei. The pattern of S-100 reactivity in tumors varied from large foci of S-100-positive cells to scattered individual S-100-positive cells. Lymph node metastases were S-100 positive, but metastatic masses in internal organs were usually S-100 negative. Although S-100 reactivity did not distinguish preneoplastic lesions from tumors or benign melanomas from malignant melanomas, identification of metastatic tumor cells clearly demonstrated malignancy.

Immunophenotype of the canine transmissible venereal tumour

The canine transmissible venereal tumour is a naturally occurring contagious round-cell neoplasia which is primarily located in the mucous membrane of the external genitalia in dogs of either sex. In order to specify the controversial cytogenetic origin of this round-cell tumour, 14 cases of canine transmissible venereal tumour, formalin- or Bouin-fixed and paraffin-embedded, were subjected to extensive immunophenotypic analysis using reagents specific to a variety of cytoplasmic or surface antigens: lysozyme, ACM1 antigen, vimentin, neuron-specific enolase, glial fibrillary acidic protein, desmin, alpha smooth muscle actin, CD3, IgG, kappa and lambda light chains, and keratin. Lysozyme immunoreactivity was detected in all cases, ACM1 antigen in 11 of 14, neuron-specific enolase in 11 of 14, vimentin in 10 of 14, glial fibrillary acidic protein in 4 of 14 and desmin in 1 of 14. All the sections were negative to keratins, alpha smooth muscle actin and CD3, whereas in five cases, perivascular tumour cells contained Ig G, kappa and lambda light chains. The immunoreactivity to lysozyme and ACM1 antigen supports the hypothesis of a histiocytic immunophenotype for the canine transmissible venereal tumour.

Blood cell markers

Cytochemistry and immunocytochemistry are important adjunctive technologies to the morphologic characterization of blood cells and hematopoietic neoplasms. Although cytochemistry is briefly discussed, the emphasis of this article is on the clinical application of flow cytometry and leukocyte monoclonal antibodies in veterinary medicine. Classification and significance of immunophenotyping in canine and feline lymphomas and immunodeficiencies such as feline immunodeficiency virus and feline leukemia virus are discussed.

Immunohistochemical characterization of canine transmissible venereal tumor

The collective immunohistochemical expression of human lysozyme, human alpha-1-antitrypsin, human CD3 antigen, calf vimentin, human keratins, human lambda light chains,canine immunoglobulins IgG, IgM, and bovine protein S-100 has been analyzed on formalin-fixed, paraffin-embedded tissue sections of 25 spontaneous canine transmissible venereal tumors (CTVT) from both genital and extragenital locations using the avidin-biotin-peroxidase complex technique. Lysozyme immunoreactivity was detected in 10/25 CTVT, alpha-1-antitrypsin in 14/25 CTVT, and vimentin in 25/25 CTVT. All CTVT cells were negative to keratins 5 + 8 of the Moll catalogue (RCK-102), S-100 protein, lambda light-chain immunoglobulins, IgG, IgM, and CD3 antigen. The intratumoral T-and B-lymphocyte infiltrate was differentiated using CD3 antigen, lambda light-chain immunoglobulins, IgG, and IgM, and this technique could be useful to evaluate the regressive or progressive growth stage of venereal tumors. Our findings support the hypothesis of a histiocytic immunophenotype for CTVT, and these staining techniques could be used in the differential diagnosis with lymphomas.

Round cell sarcomas of possible myelomonocytic origin localized at the lip of aged dogs

Four round cell tumors, situated at the lip of dogs older than 4 years of age, which could not be further classified, were examined light and electron microscopically, immunocytochemically and in part functionally and cytochemically. Immunocytochemically they were positive for vimentin, but negative for cytokeratin, desmin, neurofilament, synaptophysin, S-100 protein, neuron specific enolase, lysozyme, IgG and a pan-T-cell marker. Cell lines were established from two malignant neoplasms. In vitro, neoplastic cells had morphological, functional and cytochemical properties of myelomonocytic cells. A tumor cell-specific polyclonal rabbit antiserum reacted immunocytochemically positive with primary and recurrent tumors and metastases of the original and the three other round cell tumors. Immunoblotting demonstrated a main band with approximately 65-75 kDa. All four tumors were present in aged dogs and metastasized. They most likely represent a distinct group of malignant tumors among the canine round cell tumors.

Immunophenotypic characterization of cutaneous lymphoid neoplasia in the dog and cat

Clinical, histopathological and immunohistochemical findings are presented from a series of cutaneous lymphoid neoplasms including canine epitheliotrophic lymphoma (n = 7), canine non-epitheliotrophic cutaneous lymphoma (n = 10), canine cutaneous plasmacytoma (n = 10) and feline non-epitheliotrophic cutaneous lymphoma (n = 6). Three cases of canine epitheliotrophic lymphoma expressed the CD3 T-lymphocyte marker, but the remainder were negative for this molecule and for a panel of B-cell markers. Non-epitheliotrophic cutaneous lymphoma was shown to be predominantly of T-cell phenotype (CD3+) in the dog (eight of 10 cases) and cat (five of six cases), the remaining cases in both species being of B-cell origin, expressing the gamma heavy chain of immunoglobulin (with or without lambda light chain). One canine non-epitheliotrophic B-cell lymphoma expressed IgG of the IgG2 subclass. Two of the biopsies from dogs with cutaneous plasmacotyoma were shown to express immunoglobulin alpha chain (one with lambda chain) and two neoplasms were positive for immunoglobulin gamma chain (both with lambda chain). One of the latter immunoglobulins was of the IgG4 subclass. In the majority of all cases of cutaneous lymphoid neoplasia examined, there was a local polyclonal immune response, manifested as infiltration by a mixed population of plasma cells expressing IgG (IgG2, IgG4), IgA or IgM. In the feline tumours CD3+ small T lymphocytes were included in these infiltrates.

Ileal lymphoma in swine

Eleven cases of alimentary lymphoma affecting the ileum were observed among 26 cases of swine lymphoma detected by meat inspection in Kochi, Japan. The ileal lymphomas were located in the Peyer's patches, along with early involvement of regional lymph nodes, and showed a characteristic pattern of follicular invasion leading to diffuse growth. Following the National Cancer Institute Working Formulation, 10 neoplasms were classified as diffuse, large, noncleaved cell lymphomas and one neoplasm was a diffuse, mixed, small to large cell lymphoma. Both types of lymphoma featured numerous intermingled "starry sky" histiocytes. The lymphoma cells tended to infiltrate into the muscular layer of the ileum in an "Indian file" pattern. Two cases also showed transserosal metastasis into the abdomen and leukemic change. The lymphoma cells showed membrane positivity for alkaline phosphatase and diffuse cytoplasmic staining for acid phosphatase and non-specific esterase. Monoclonal intracytoplasmic immunoglobulins were demonstrated in nine neoplasms (IgM-lambda in seven, IgG-lambda in one, and IgG-kappa in one). In the areas of follicular invasion, an attenuated network of follicular dendritic cells was visualized via an antiserum against the beta subunit of S-100 protein. Ultrastructurally, strands of dilatated rough endoplasmic reticulum and scattered or clustered dense bodies were noted. When compared with feline and human alimentary lymphoma, including Burkitt's lymphoma, the present neoplasms possessed distinctive features, such as originating in Peyer's patches, transserosal metastasis, and predominantly large B cell type with IgM-lambda type immunoglobulin expression, although some features were similar.

Canine mast cell tumors: a comparison of staining techniques

Twelve histochemical methods; affinity staining with avidin peroxidase, wheat germ agglutinin, and concavalin-A agglutinin; and an immunohistochemical stain with Kp1 (CD68) antibody were compared for their relative effectiveness in staining canine mast cell tumors. Stains were compared in 28 mast cell tumors and 19 histiocytomas. The effectiveness of the histochemical methods and the lectins decreased as the mast cells became less differentiated. None of the staining methods were positive on histiocytomas. Periodic acid-Schiff (PAS) gave positive results in a few cases of mast cell tumors where other histochemical stains were negative. Although avidin peroxidase and Kp1 antibody stained more mast cell tumors than any other method, they did not differ significantly from Luna's method, toluidine blue pH 0.5, toluidine blue pH 4.5, alcian blue pH 2.5, safranin O, Unna's method, and Giemsa. No stain was ideal for the diagnosis of canine mast cell tumors; however, this study suggests that the use of avidin peroxidase, Kp1 antibody, and PAS may give additional information for individual poorly differentiated tumors without substantial increase in time or cost.

Immunohistochemical detection of melanoma-associated antigens on formalin-fixed, paraffin-embedded canine tumors

Seven monoclonal antibodies (Moabs), recognizing melanoma-associated antigens in human tissues, were evaluated for their ability to immunohistochemically stain formalin-fixed, paraffin-embedded canine melanomas. Only 2 Moabs, designated human melanosome-specific antigen (HMSA)-1 and HMSA-5, stained routinely processed canine melanomas, staining 21/35 (60%) and 24/35 (69%), respectively. Twenty-nine of 35 (83%) melanomas tested were stained if results of the 2 Moabs were combined. Monoclonal antibody HMSA-1 also stained neoplastic cells of 10/35 (29%) tumors of nonmelanocytic origin and some neurons and salivary gland epithelial cells in normal canine tissues. However, Moab HMSA-1 staining in the nonmelanocytic tumors, consisting of small, discrete periodic acid-Schiff-positive cytoplasmic droplets, was readily distinguishable from the diffusely granular, cytoplasmic staining of melanocytic tumors. In addition to melanomas, Moab HMSA-5 stained melanocytes and some melanin-containing tumor cells of a pigmented basal cell tumor and melanocytes in normal canine skin. Monoclonal antibodies HMSA-1 and HMSA-5 immunohistochemically identified the majority of canine melanomas, had limited and distinguishable staining in normal tissues and nonmelanocytic tumors, and therefore may be a useful adjunct for the diagnosis of canine melanoma in formalin-fixed, paraffin-embedded tissues.

Histopathologic features and post-surgical sequelae of 57 cutaneous neoplasms in ferrets (Mustela putorius furo L.)

The study of the signalment, histomorphologic features, and post-surgical clinical progress of 57 cutaneous neoplasms in 55 domestic ferrets (Mustela putorius furo L.) was based on diagnostic pathologic accessions (1987-1992) from 142 ferrets. Mean age of the group was 4.3 years; 31/54 (57%) were female and 23/54 (43%) were male. Thirty-three (58%) of the cutaneous neoplasms were basal cell tumors. The mean age of ferrets with basal cell tumor was 5.2 years, and 23/33 (70%) were female. Histologically, the basal cell tumors were composed of well-differentiated basaloid epithelial cells with various degrees of squamous and sebaceous differentiation, similar to those seen in basal cell neoplasms of dogs. Nine of the 57 (16%) cutaneous neoplasms were mastocytomas. The mean age of ferrets with mastocytoma was 4.1 years; four were male, four were female, and the sex of one was unrecorded. Histologically, the mastocytomas were composed of well-differentiated mast cells with few eosinophils, similar to cutaneous mastocytomas of domestic cats. The mast cells had a small number of metachromatic cytoplasmic granules, and in six of eight neoplasms the granules had an affinity for conjugated avidin-peroxidase. Six of the cutaneous neoplasms (11%) were fibromas. The mean age of ferrets with fibroma was 2.7 years; 5 (83%) were male. Two cutaneous hemangiomas (4%) were in females, which were 4 and 5 years of age. There was one each hemangiosarcoma, cutaneous polyp, anal gland adenocarcinoma, lymphosarcoma of the prepuce and inguinal lymph node, and adenocarcinoma of the prepuce.

Malignant fibrous histiocytomas in dogs and cats: an immunohistochemical study

Immunohistochemical staining was performed on seven canine and 10 feline soft tissue tumours histologically diagnosed as malignant fibrous histiocytomas (MFHs) or MFH-like tumours, and eight other histologically specified tumours (non-MFH). This was done to determine if commercially available antibodies that are used routinely in human diagnostic pathology for MFHs would express the same immunohistochemical patterns in canine and feline MFHs and MFH-like tumours. The antibodies were directed against human alpha 1-anti-trypsin (AT), human alpha 1-anti-chymotrypsin (ACT), human lysozyme, bovine S-100 protein and human desmin. AT did not show any immunoreactivity in the tissues investigated. Except for one MFH, all canine MFHs and other soft tissue tumours with a 'histiocytic' character stained for lysozyme and not for S-100. Six out of seven canine MFHs and MFH-like tumours stained positive for desmin as did most non-MFH sarcomas. Most of the canine and feline MFHs and MFH-like tumours were positive for ACT. These findings for ACT staining in canine and feline MFHs and MFH-like tumours are in agreement with the findings in human MFHs. The immunohistochemical results of canine MFHs and MFH-like tumours were different from those in cats. Feline MFHs differed from canine MFHs for both lysozyme and desmin staining.

Immunocytochemical identification of a bovine peritoneal mesothelioma

Peritoneal mesotheliomas are uncommon among cows although there has been an increase in the frequency of diagnosis of this neoplasia in the past few years. The case of a 2 year old cow is described. On post-mortem examination, several nodules of variable size were found in the peritoneal cavity. These nodules fused together, but they did not go deep into the organs. Histologically, such nodules were formed by a population of fusiform cells of malignant morphological character and sarcomatous appearance. Immunocytochemical study, using P.A.P. techniques, showed a highly positive reaction towards vimentin and a negative reaction towards wide-spectrum cytokeratins, hence suggesting a mesenchymal origin of the neoplasia. According to the histopathological study, a multifocal peritoneal mesothelioma of sarcomatous appearance was identified.

Lingual rhabdomyoma in a dog

A neutered male mixed breed dog, with a history of progressive dyspnoea, was presented for surgical removal of an enlarging lingual neoplasm (60 x 40 x 70 mm), previously diagnosed as a granular cell tumour. Microscopically the excised neoplasm comprised sheets of pleomorphic cells; large granular eosinophilic cells, multinucleated giant cells and smaller angular cells. A tentative diagnosis of rhabdomyoma was based on the light microscopic changes. This diagnosis was confirmed by the ultrastructural identification of bundles of intracytoplasmic filaments (interpreted to be myosin) within the neoplastic cells and the strong positive reaction of these cells to markers for "muscle-specific" actin (HHF35).

Distinctive unclassified mesenchymal tumor of the digit of dogs

Four examples of a mesenchymal tumor of undetermined histogenesis occurred in three mixed-breed dogs and one Yorkshire terrier. All tumors occurred as solitary, soft to firm, solid, tan, and ulcerated masses in the digits of dogs aged 11 to 15 years. The compact cellular tumor had cells with anisokaryotic round, oval, or irregular nuclei, some of which were multinucleated. The neoplastic cells appeared to arise in the tissue near the third phalanx in the area of dense collagenous trabeculae located proximal to the fat pad and sweat glands. The unclassifiable cells had some features of histiocytes by transmission electron microscopy, but failed to stain for lysozyme and alpha-1-antichymotrypsin, markers for monocyte-macrophage derived cells. Immunohistochemically, the cells stained for vimentin but not for cytokeratins, desmin, S-100 protein, epithelial membrane antigen, alpha-lactalbumin, lysozyme, alpha-1-antichymotrypsin, alpha-lactalbumin, casein, and heavy and light chain immunoglobulins. The combined findings of light and transmission electron microscopy and immunohistochemistry exclude tumor histogenesis from an epithelial cell, melanocyte, mast cell, plasma cell, Schwann cells, and Merkel cell.

Identification of immunoglobulin light chains in canine extramedullary plasmacytomas by thioflavine T and immunohistochemistry

Extramedullary plasmacytomas were studied in 29 dogs. The site at which tumors occurred and the age and sex of the dogs were similar to those in previous reports. The skin of the digits, chin, ear, and lip represented the most common (17/29) tumor sites. Males and females were equally represented, and tumors occurred in middle-aged to old dogs (mean age, 9.0 years). A breed predilection was seen in the Cocker Spaniel (n = 7; 24%); Cocker Spaniels represented only 4% (210/4,725) of the submissions during the same period. Tumors were stained with immunohistochemical markers (lambda light chain, K light chain) and thioflavine T. Immunoreactivity was limited to either lambda or K light chains, consistent with a monoclonal plasma cell population. The majority of tumors expressed lambda light chains, consistent with previously reported canine plasma cell dyscrasias. Thioflavine T cytoplasmic fluorescence was seen in the majority (18/29) of plasmacytomas and with inflammatory plasma cells present in control specimens. Other round cell neoplasms (lymphosarcoma, histiocytoma, and mastocytoma) were negative with thioflavine T, indicating that positive staining with thioflavine T was specific for plasma cells (neoplastic and inflammatory). This study confirms by immunohistochemistry that canine extramedullary plasmacytomas disproportionately express lambda light chains and establishes thioflavine T staining as a rapid histochemical method for diagnosis of these tumors.

Clinicopathologic characterization of canine juvenile cellulitis

The syndrome of canine juvenile cellulitis was observed and characterized throughout its clinical course when it occurred spontaneously in a litter of dogs. Histologically, pyogranulomatous inflammation was seen in facial skin and mandibular and superficial cervical lymph nodes of affected dogs. The predominant inflammatory cell characterized by light and electron microscopy and by immunohistochemical staining was an epithelioid macrophage. The same pyogranulomatous inflammatory process was seen in a lymph node anatomically distant from the site of apparent disease. Interestingly, a littermate with neither clinically evident dermal lesions nor lymphadenopathy had histologic evidence of a milder, but similar inflammatory process in a mandibular lymph node. The observation of canine juvenile cellulitis in clusters of dogs between 1 and 4 months of age and its apparent systemic nature suggest an infectious etiology. Bacterial, fungal, or viral agents were not isolated from affected lymph nodes. Attempts to transfer the disease by inoculation of neonatal puppies with tissue from affected dogs were also unsuccessful.

An immunohistochemical study of canine tissues with vimentin, desmin, glial fibrillary acidic protein, and neurofilament antisera

In a wide range of canine tissues the immunoreactivity with commercially available antisera against intermediate filament antigens viz. vimentin, desmin, glial fibrillary acidic protein (GFAP) and neurofilament proteins, was studied. In addition, the results of formalin and Carnoy fixation were compared. Carnoy fixation appeared to result in optimal reactivity for all antisera. Epithelial cells did not react with any of the antisera, with exception of ovarian surface epithelium, which showed staining with the vimentin and desmin antisera. The vimentin antiserum induced staining of several cell types viz. fibroblasts, endothelial cells, chondrocytes, Schwann cells, ependymal cells, astrocytes, Leydig cells, synovial cells, podocytes and some parietal cells of Bowman's capsule. Sertoli cells showed a faint staining reaction. Muscle cells in various tissues reacted with the desmin antiserum. In the kidney a varying number of parietal cells appeared to react as did a restricted number of epithelial cells of proximal tubules and loops of Henle. GFAP reactivity was confined to glial cells, predominantly fibrous astrocytes, Schwann cells and axons. Additionally, some neuronal cell bodies in peripheral ganglia showed staining of varying intensity. Neurofilament staining was restricted to axons and some neurons. The immunoreactivity of canine tissues with these antisera is compared to findings in other species. The results confirm a broad interspecies cross-reactivity of these antisera. They can be used in studying the nature of canine tissues.

Keratin staining of canine epithelial tissues by a polyclonal antiserum

The keratin distribution pattern in various canine epithelial tissues has been studied using a commercially available rabbit antiserum, raised against human skin keratins, in an immunoperoxidase staining method with the peroxidase-antiperoxidase complex (PAP). The staining results of two fixation methods were compared. Paraffin sections after fixation in Carnoy's solution showed optimal results, whereas paraffin sections after fixation in 10% buffered formalin resulted in a strongly reduced keratin staining reaction. Keratinizing and non-keratinizing stratified epithelial showed a strong staining reaction. Glandular epithelium and the non-stratified epithelia of internal organs e.g. liver, kidney and intestine did not react with the antiserum. However, glandular ductal epithelium, myoepithelial cells and basal cells in various epithelial tissues showed a positive staining reaction. The results indicate the presence of different keratin types in these canine epithelial tissues. The keratin distribution pattern is compared with the distribution pattern observed in tissues of other species.

Cutaneous plasmacytomas in dogs: a morphologic and immunohistochemical study

Forty-nine cutaneous plasmacytomas in 46 dogs were studied. Tumors occurred at solitary sites in middle-aged to old dogs (mean age, 9.7 years) and most commonly involved the skin of the digits, lips, and ears. Initial diagnosis was made on the basis of light microscopic morphologic findings. Tumors were graded according to the extent of cellular differentiation and immunoreactivity to a panel of immunohistochemical markers (cytokeratins, canine IgG F[ab]2, neurofilament, neuron-specific enolase, S-100 protein, and vimentin). Immunoreactivity was limited to antibodies directed at canine IgG F(ab)2 and vimentin. Vimentin immunoreactivity was usually greater than that of canine IgG F(ab)2, but there was no correlation between immunoreactivity and histologic grade of the tumors. Thirty-six of 39 dogs (92.3%) followed (mean follow-up, 13 months) were cured by surgical excision. The results of this study indicate that canine cutaneous plasmacytomas are benign neoplasms that should be included in the differential diagnosis of cutaneous round cell tumors in dogs.

An immunohistochemical study of canine extramedullary plasma cell tumours

Twenty-three cases of dog plasma cell tumours were investigated for the presence of monoclonal cytoplasmic immunoglobulin light chain types and heavy chain classes. The peroxidase-antiperoxidase method was applied to formalin-fixed, paraffin-embedded tissues, available as stored blocks. Twenty tumours showed a monoclonal light chain type and heavy chain class pattern, two showed a monoclonal light chain type and a biclonal heavy chain class pattern, findings which confirmed the neoplastic nature of the plasma cells. One tumour did not stain with any of the antisera. The results indicate that the method reliably establishes the monoclonality and, consequently, the neoplastic nature of plasma cell proliferations.