Subcutaneous Panniculitis-Like T-cell Lymphoma in Dogs: Morphologic and Immunohistochemical Classification

Subcutaneous panniculitis-like T-cell lymphoma: Morphological, immunophenotypical and clonality assessment in six cats

BACKGROUND

Primary cutaneous lymphoma represents 0.2%-3% of all feline lymphomas, with nonepitheliotropic lymphomas being the most common. In humans and dogs, subcutaneous panniculitis-like T-cell lymphoma (SPTCL) is a primary nonepitheliotropic lymphoma with a T-cell phenotype developing in the subcutis and often mimicking inflammation.

OBJECTIVE

The aim of this report is to describe pathological, phenotypical and clonal features of SPTCL in cats.

ANIMALS

Six cats with SPTCL were included in this study.

MATERIALS AND METHODS

Skin biopsies were formalin-fixed, routinely processed and stained. Histological and immunohistochemical investigation for anti-CD18, CD204, CD79a, CD20, CD3, FeLVp27and FeLVgp70 and clonality assessment were performed.

RESULTS

Four male and two female domestic shorthair cats, mean age 11.2 years, developed SPTCL in the abdominal (three), inguinal (two) and thoracic (one) regions. Variably pleomorphic neoplastic lymphoid cells were present in the panniculus in percentages, expanding the septa (six of six) and extending into fat lobules in one of six cats. Tumours were associated with elevated numbers of neutrophils (five of six), lesser macrophages (six of six) and variable necrosis (six of six). Neoplastic cells expressed CD3+ (six of six), with clonal T-cell receptor rearrangement detected in five of six cats.

CONCLUSIONS AND CLINICAL RELEVANCE

This is the first description of SPTCL in cats. Lesions can be confused with panniculitis, leading to delay in diagnosis and therapy. Awareness of this neoplastic disease is relevant to avoid misdiagnoses and to gain greater knowledge about the disease in cats.

Pattern analysis for the diagnosis of inflammatory skin lesions in domestic animals: An overview

Pattern analysis of inflammatory skin diseases is a technique that offers a systematic approach to the histologic diagnosis of skin diseases. First introduced to human dermatopathology in the 1970s, it was widely adopted by veterinary pathologists for the histologic diagnosis of skin diseases in animals. As the inflammatory pattern reflects, to varying extents, aspects of the underlying disease pathogenesis, its use has contributed to the recognition of novel skin diseases in domestic animals, particularly in dogs and cats. Alternative diagnostic approaches used in human dermatopathology, such as "tissue-reaction pattern" and a purely "anatomic approach" have not been as widely used in veterinary pathology. However, veterinary pathologists often combine pattern analysis with anatomic and etiologic factors. This overview outlines the technique, introduces the patterns, and discusses advantages and limitations of pattern analysis in veterinary diagnostic dermatopathology. While molecular analytic techniques and image informatics will undoubtedly prove to be revolutionary in many areas of diagnostic pathology, it is recognized in both human and veterinary arenas that the light microscopic interpretation of hematoxylin and eosin-stained tissue sections will remain the mainstay of routine dermatopathology diagnosis for the foreseeable future.

Prognostic clinical and histopathological features of canine cutaneous epitheliotropic T-cell lymphoma

Canine cutaneous epitheliotropic T-cell lymphoma is a neoplasm with heterogeneous clinical and histopathological presentations. Survival times and responses to therapy are variable, and indicators to predict outcomes are lacking. Clinical and histopathological parameters from 176 archival cases from the University of Pennsylvania and University of Bern (2012-2018) were investigated for associations with clinical outcomes. Histopathological evaluation used digitized whole slide images and QuPath software. Cases included 107 female and 69 male dogs from 48 breeds, with a mean age of 10.4 years. Most common clinical signs were erythema (n = 131), crusting (n = 108), and scaling (n = 102). Affected sites were haired skin (n = 159), lip (n = 74), nasal planum (n = 49), and paw pads (n = 48). The median survival time (MST) was 95 days (1-850). Dogs had 4.26-fold and 2.82-fold longer MST when treated with chemotherapy and prednisone, respectively, than when receiving supportive care. Haired skin involvement (hazard ratio [HR]: 2.039, 95% confidence interval [CI]: 1.180-3.523), erosions/ulcers (HR: 1.871, 95% CI: 1.373-2.548), nodules (HR: 1.496, 95% CI: 1.056-2.118), and crusting (HR: 1.454, 95% CI: 1.061-1.994) were clinical parameters predicting poor outcomes, whereas complete posttherapeutic clinical remission (HR: 0.469, 95% CI: 0.324-0.680) and a stable disease (HR: 0.323, 95% CI: 0.229-0.456) were associated with longer survival. Histopathological features associated with the increased risk of death were extensive infiltration of the panniculus (HR: 2.865, 95% CI: 1.565-4.809), mitotic count ≥7/high-power field (HR: 3.027, 95% CI: 2.065-4.439), cell diameter ≥10.0 µm (HR: 2.078, 95% CI: 1.281-3.372), and nuclear diameter ≥8.3 µm (HR: 3.787, 95% CI: 1.647-8.707).

Immunopathogenesis of canine chronic ulcerative stomatitis

Canine Chronic Ulcerative Stomatitis is a spontaneously occurring inflammatory disease of the oral mucosa. An immune-mediated pathogenesis is suspected though not yet proven. We have recently reported on the clinical and histologic features, and identification of select leukocyte cell populations within the lesion. A clinical and histologic similarity to oral lichen planus of people was proposed. In the present study, these initial observations are extended by examining lesions from 24 dogs with clinical evidence of chronic ulcerative stomatitis. Because dogs with chronic ulcerative stomatitis often have concurrent periodontal disease, we wondered if dental plaque/biofilm may be a common instigator of inflammation in both lesions. We hypothesized that dogs with chronic ulcerative stomatitis would exhibit a spectrum of pathologic changes and phenotype of infiltrating leukocytes that would inform lesion pathogenesis and that these changes would differ from inflammatory phenotypes in periodontitis. Previously we identified chronic ulcerative stomatitis lesions to be rich in FoxP3+ and IL17+ cells. As such, we suspect that these leukocytes play an important role in lesion pathogenesis. The current study confirms the presence of moderate to large numbers of FoxP3+ T cells and IL17+ cells in all ulcerative stomatitis lesions using confocal immunofluorescence. Interestingly, the majority of IL17+ cells were determined to be non-T cells and IL17+ cell frequencies were negatively correlated with severity on the clinical scoring system. Three histologic subtypes of ulcerative stomatitis were determined; lichenoid, deep stomatitis and granulomatous. Periodontitis lesions, like stomatitis lesions, were B cell and plasma cell rich, but otherwise differed from the stomatitis lesions. Direct immunofluorescence results did not support an autoantibody-mediated autoimmune disease process. This investigation contributes to the body of literature regarding leukocyte involvement in canine idiopathic inflammatory disease pathogenesis.

CD30 Cross-Reactivity and Expression in Feline Normal Tissues and Lymphomas

CD30 is a transmembrane glycoprotein of the tumor necrosis factor receptor superfamily included in the diagnostic algorithm of human cutaneous, anaplastic large cell and Hodgkin lymphomas and represents an optimal therapeutic target for CD30⁺ tumors. Similar diagnostic and therapeutic approaches are largely missing for feline lymphomas. Cross-reactivity of the antihuman CD30 receptor clone Ber-H2 was investigated in feline lymphomas. Comparative analysis of feline and human CD30 identified 61% identity of the amino acid sequence, with 100% identity of the main sequence of the epitope targeted by the antibody (RKQCEPDYYL). CD30 expression in normal feline tissues was restricted to rare lymphoid cells in perifollicular and interfollicular lymph node areas and in the thymic medulla. In feline lymphoma, CD30 was expressed in 4 of 33 (13%) T-cell lymphomas, 3 of 22 (14%) B-cell lymphomas, and 5 of 7 (71%) mixed-cell lymphomas, showing diffuse (1/5) or multifocal (4/5) positivity restricted to neoplastic multinucleated lymphoid cells and binucleated cells consistent with Reed-Sternberg-like cells. Based on the human classification system, cell morphology, expression of multiple markers (mixed cell components), and CD30 positivity, these cases were considered most consistent with classical Hodgkin-like lymphoma (HLL). The other 2 mixed-cell lymphomas were CD30 negative and thus most consistent with either T-cell-rich large B-cell lymphoma (TCRLBCL) or nodular lymphocyte-predominant Hodgkin lymphoma (NLPHL). These findings provide multiple data supporting the cross-reactivity of the Ber-H2 anti-CD30 clone in feline tissues and give evidence of the usefulness of CD30 in the diagnostic evaluation of feline lymphoma.

Primary Colorectal Follicular Lymphoma in 3 Dogs

Primary colorectal follicular lymphomas are rare indolent lymphoid neoplasms in humans that have not been reported in dogs. We describe 3 cases of primary colorectal follicular lymphoma in dogs with histologic and immunohistochemical features similar to their human counterpart. Initial clinical signs in all dogs included tenesmus, hematochezia, and a palpable rectal mass. Two dogs were castrated males and 1 an intact female, between 9 months and 2 years of age, and of varied breeds. All 3 cases of colorectal follicular lymphoma were characterized by proliferation of follicular germinal centers with no polarity or mantle zone and were composed of centrocytes admixed with fewer centroblasts. By immunohistochemistry, lymphoid cells expressed CD20, BCL2, and BCL6 and lacked expression of CD3, CD5, and cyclin D1. Polymerase chain reaction for rearrangements of the immunoglobulin heavy chain confirmed a monoclonal population in all cases. In 2 of the 3 cases, a solitary nodular colorectal mass was excised and appeared curative; however, the third case had multiple colorectal masses and the animal developed multicentric lymphoma. This case series immunohistochemically characterizes and distinguishes colorectal follicular lymphoma from atypical lymphoid hyperplasia.