Equine Cutaneous Mast Cell Tumours Exhibit Variable Differentiation, Proliferation Activity and KIT Expression

Clinical, pathologic, and molecular characterization of a non-metastatic multicentric cutaneous mast cell tumor in a cow

Cutaneous mast cell tumors are rarely reported in cattle. Although mutations in the c-KIT gene have been shown to play a central role in the oncogenesis of canine mast cell tumors, few data are available in cattle. This report describes the clinical, histologic, immunohistochemical, and genetic features of a multicentric cutaneous mast cell tumor in an adult cow. An 11-year-old Prim'Holstein cow was presented for a 5-month history of multiple skin nodules. Cytologic and histologic analyses of the nodules led to a diagnosis of mast cell tumors. Immunohistochemical analysis for KIT expression showed a moderate to strong signal in neoplastic mast cells with a cytoplasmic and membranous pattern. Sequencing of the c-KIT gene coding sequence revealed no mutation. Despite partial response after corticosteroid treatment, euthanasia was elected. No metastases to the lymph nodes, spleen, and liver were identified at post-mortem and histologic examinations.

Histological evidence of superficial inflammation is associated with lower recurrence of equine sarcoids following surgical removal: A follow-up study of 106 tumours in 64 horses

Although the equine sarcoid is the most common skin neoplasm in domesticated horses, histopathological characteristics have not previously been evaluated for association with recurrence. The aim of this retrospective cohort study was to investigate clinical and histopathological features of excised equine sarcoids and to evaluate their association with recurrence at the original surgical site and at new sites. Clinical records and excisional biopsies from 106 equine sarcoids from 64 horses referred to Leahurst Equine Hospital, University of Liverpool, between March 2010 and February 2015 were retrieved. Biopsies were re-evaluated histologically. Clinical data were obtained from hospital records, and owner-reported follow-up data were obtained by telephone questionnaire. Associations between clinical and histopathological features of sarcoids and their recurrence at the surgical site were determined using uni- and multivariable mixed effects logistic regression. Recurrence of sarcoids at the surgical site occurred in 30 horses (46.9%). Sarcoids developed at a distant site in 21 horses (32.8%). In the final mixed effects logistic regression model, only superficial inflammation was associated with reduced odds of recurrence at the surgical site (adjusted odds ratio, 0.32; 95% confidence intervals, 0.10-0.96; P = 0.04). This suggests that the inflammatory process may play a role in protecting horses against the recurrence of sarcoids.

Multinodular Malignant Cutaneous Mast Cell Tumor in a Horse With Generalized Pruritus and Reactive Fibrosis: A Case Report

Mast cell tumor (MCT) has long been considered as an uncommon neoplasm in horses. Cytological and behavioral evidence of its malignancy is usually lacking, and only a few reports have described MCT displaying malignant behavior. An 18-year-old Friesian stallion presented with a one-year history of intermittent and progressive skin lesions on the left forelimb associated with intense, generalized pruritus and apathy temporarily responsive to glucocorticoids and antibiotics. The horse was alert and responsive with poor body condition and marked generalized pruritus. The left forelimb was markedly enlarged and surrounded by numerous firm 2- to 20-cm masses that were ulcerated and focally necrotic. A 7-cm round firm mass was observed on the left dorsal neck. Dermatological examination revealed generalized moth-eaten alopecia and scaling with erosions and ulcers secondary to pruritus. A direct skin smear from the affected leg showed severe eosinophilic inflammation and neutrophilic inflammation with pleomorphic bacteria. Histopathology of the skin and biopsies of the underlying tissues revealed an abundant population of atypical mast cells consistent with a malignant MCT. The horse was euthanized and necropsy revealed a marked fibrous reaction on longitudinal sections of the affected limb, and the tumor could be detected on only a few histological slides. Diagnosis of equine MCT can be challenging because of the massive accompanying fibrous reaction. Mast cell tumor should be suspected in the presence of eosinophilic infiltration of the affected tissue and in cases of generalized pruritus not attributable to other causes.

Comparative aspects of mast cell neoplasia in animals and the role of KIT in prognosis and treatment

Mast cell neoplasia clinical presentation and biological behaviour vary considerably across mammalian species, ranging from a solitary benign mass to an aggressive systemic malignancy. Mutations in the KIT Proto‐Oncogene Receptor Tyrosine Kinase (KIT) gene are common molecular abnormalities involved in mast cell tumorigenesis. KIT mutations often occur in dog, cat and human neoplastic mast cells and result in altered Kit protein structure and function. In dogs, certain KIT mutations are associated with more malignant and lethal disease. In contrast, KIT mutations in feline and human mast cell neoplasms are not correlated with prognosis, but are of value in diagnosis and treatment planning in humans. KIT genetic abnormalities have not been well investigated in other species, although aberrant cytoplasmic Kit protein staining detected in neoplasms of the ferret, horse and cow resembles aberrant Kit staining patterns detected in neoplastic mast cells of dogs, cats and humans. Mutations within KIT are classified as either regulatory‐type or enzymatic pocket‐type mutations according to their location within the KIT Proto‐Oncogene. Mutations within the enzymatic pocket domain confer tumour resistance to tyrosine kinase inhibitors (TKIs). Hence, knowledge of tumour KIT mutation status adds valuable information for optimizing patient treatment strategies. The use of TKIs in combination with conventional chemotherapeutics has opened a new treatment avenue for patients unresponsive to existing drugs. This review highlights the similarities and differences of mast cell neoplasia in mammals with a special focus on the involvement of KIT in the canine and feline forms in comparison to human mast cell neoplasia.

Histocytic-like Atypical Mast Cell Tumours in Horses

This report describes a series of four equine mast cell tumours (MCTs) with atypical morphological features. The tumours were 1-2 cm in diameter and mostly localized to the eyes (one eyelid, two conjunctiva). Histologically, they were composed of very large (up to 35 μm) round pleomorphic cells with a large central to paracentral nucleus and abundant granular cytoplasm. A large number of viable mature eosinophils were detected intermingled with the large round cells. Histochemical staining (toluidine blue and Perls' Prussian blue) and immunohistochemistry (KIT, mast cell tryptase, lysozyme and proliferating cell nuclear antigen) confirmed the mast cell origin of the atypical cells and identified an aberrant KIT protein expression in three cases. Based on morphological and immunohistochemical features, we propose to call the lesions equine histiocytic-like atypical MCTs.

Equine ocular mast cell tumor: histopathological and immunohistochemical description

This report describes an ocular mast cell tumor in a 13-year-old female sport horse. Clinical examination revealed a solitary firm mass located in the ocular mucosa, protruding from behind the left lower eyelid. The lesion was surgically removed and submitted to histopathology. Microscopically, the mass was composed of sheets of well-differentiated neoplastic round cells circumscribed by delicate connective tissue. Positive Giemsa and Toluidine Blue staining confirmed the presence of cytoplasmic granules. Neoplastic cells showed strong membranous and mild diffuse cytoplasmic immunoreactivity for c-KIT and a low KI-67 proliferative index. Based on these findings, a diagnosis of ocular mast cell tumor was made. Six months after surgical removal, no evidence of ocular lesion recurrence was detected.

Nidovirus-Associated Proliferative Pneumonia in the Green Tree Python (Morelia viridis)

In 2014 we observed a noticeable increase in the number of sudden deaths among green tree pythons (Morelia viridis). Pathological examination revealed the accumulation of mucoid material within the airways and lungs in association with enlargement of the entire lung. We performed a full necropsy and histological examination on 12 affected green tree pythons from 7 different breeders to characterize the pathogenesis of this mucinous pneumonia. By histology we could show a marked hyperplasia of the airway epithelium and of faveolar type II pneumocytes. Since routine microbiological tests failed to identify a causative agent, we studied lung tissue samples from a few diseased snakes by next-generation sequencing (NGS). From the NGS data we could assemble a piece of RNA genome whose sequence was <85% identical to that of nidoviruses previously identified in ball pythons and Indian pythons. We then employed reverse transcription-PCR to demonstrate the presence of the novel nidovirus in all diseased snakes. To attempt virus isolation, we established primary cultures of Morelia viridis liver and brain cells, which we inoculated with homogenates of lung tissue from infected individuals. Ultrastructural examination of concentrated cell culture supernatants showed the presence of nidovirus particles, and subsequent NGS analysis yielded the full genome of the novel virus Morelia viridis nidovirus (MVNV). We then generated an antibody against MVNV nucleoprotein, which we used alongside RNA in situ hybridization to demonstrate viral antigen and RNA in the affected lungs. This suggests that in natural infection MVNV damages the respiratory tract epithelium, which then results in epithelial hyperplasia, most likely as an exaggerated regenerative attempt in association with increased epithelial turnover.IMPORTANCE Novel nidoviruses associated with severe respiratory disease were fairly recently identified in ball pythons and Indian pythons. Herein we report on the isolation and identification of a further nidovirus from green tree pythons (Morelia viridis) with fatal pneumonia. We thoroughly characterized the pathological changes in the infected individuals and show that nidovirus infection is associated with marked epithelial proliferation in the respiratory tract. We speculate that this and the associated excess mucus production can lead to the animals' death by inhibiting normal gas exchange in the lungs. The virus was predominantly detected in the respiratory tract, which renders transmission via the respiratory route likely. Nidoviruses cause sudden outbreaks with high rates of mortality in breeding collections, and most affected snakes die without prior clinical signs. These findings, together with those of other groups, indicate that nidoviruses are a likely cause of severe pneumonia in pythons.