Confocal Laser Scanning Analysis of an Equine Oral Mast Cell Tumor with Atypical Expression of Tyrosine Kinase Receptor C-KIT

Principles of Tumor Biology

Cancer is disease of the genome. The Hallmarks of cancer are a way of thinking of cancer to help rationalize what occurs in this disease process. A solid tumor is a complex of normal and neoplastic cells, arising through an evolutionary process to survive and grow. By understanding how normal cellular mechanisms are subverted to promote cancer we can refine our approach to improve outcomes. It gives us opportunities to prevent some cancers and allowing earlier diagnosis. We can refine conventional diagnostic tools and give more accurate prognoses. It offers novel targets to improve treatment of cancers, allowing personalized medicine.

Invasive leiomyosarcoma involving the tongue of an Arabian mare

A 10 year-old endurance Arabian mare was presented with an invasive, firm, multilobulated mass at the left ventral face of the tongue. The mare had a history of four months of ptyalism, dysphagia, severe halitosis, and dysmastication. The Evaluation of the horse included physical and oral examination, complete blood count and serum biochemistry profile, computed tomography evaluation of the head, and histopathology of the mass. The computerized tomography (CT) head scan showed the homogeneous mass in the oral cavity confirming the degree of invasion on the tongue, as well as a small mineral focus at the left dorsal mandibular border and increased density of the submandibular lymph nodes. At necropsy, gross findings in the oral cavity revealed an irregular, nodular and partially ulcerated mass at the level of the body of the tongue in the ventral aspect, with a size of approximately 10 × 15 × 8 cm. Histologically, the tongue revealed a neoplastic process of mesenchymal muscle origin. The tumor cells showed distinctive morphological and architectural patterns in some areas. An immunohistochemistry panel was done yielding a positive reaction for Calponin and Desmin, confirming diagnostics of as a soft tissue leiomyosarcoma in the tongue. Immunohistochemistry results, in combination with histopathologic morphology, were suggestive of a leiomyosarcoma originating in the perivascular wall tissue. Oral leiomyosarcoma are very rare in veterinary medicine, and to the authors' knowledge, this is the first case report to utilize histopathology, immunohistochemistry and imaginology to describe oral leiomyosarcoma in a horse.

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

Equine cutaneous mast cell tumours (CMCTs) are generally considered to be benign skin lesions, although recurrent and multicentric tumours have been described. For canine CMCTs, grading and prognostic approaches are well established and aberrant KIT expression as well as high proliferation indices are associated with poor outcome. However, in the case of equine CMCTs, morphological features, proliferative activity and KIT expression pattern have not been assessed or related to biological behaviour, and there is discussion as to whether CMCTs are true neoplastic processes. The present study describes 45 equine CMCTs in terms of their morphology and KIT and PCNA expression by immunohistochemistry. KIT expression was classified as membranous (I), cytoplasmic and focally stippled (II) or diffuse cytoplasmic (III). A large proportion of the tumours were multinodular or diffuse dermal infiltrates of mast cells with mild anisokaryosis, a low proliferative rate and a dominance of KIT pattern I, representing well-differentiated CMCTs. In approximately one third of the cases, the mast cells exhibited more infiltrative growth, moderate to marked anisokaryosis and a higher degree of proliferation. These were classified as poorly differentiated CMCTs and exhibited only KIT patterns II and III. These findings indicate that there is a subgroup of poorly differentiated equine CMCTs, in which there is an association between aberrant KIT expression, high proliferative rate and potential aggressive behaviour, all features that confirm at least the poorly differentiated CMCT as a true neoplastic processes.

Adenocarcinoma involving the tongue and the epiglottis in a horse

Tumors involving the oral cavity of the horse are uncommon. No cases of equine adenocarcinoma on the dorsum of the tongue have been reported in the literature. We report a case of adenocarcinoma located on the dorsum of the posterior one-third of the tongue in a 29-year-old gelding with severe dysphagia. Endoscopy revealed an epiglottis involvement, and histology was consistent with adenocarcinoma arising from minor salivary glands, which was associated with a severe fungal colonization of affected tissues. The goals of this report are to present an uncommon case of dorsum of the tongue-associated neoplasia and to highlight the association with atypical fungal colonization, to review the literature and to discuss possible clinical approach and prognosis.

Histologic Characteristics and KIT Staining Patterns of Equine Cutaneous Mast Cell Tumors

Mast cell tumors are uncommon in horses and typically have a benign clinical course, but there are occasional reports of more aggressive behavior. The objective of this study was to review histologic features and KIT expression patterns of 72 previously diagnosed equine cutaneous mast cell tumors to determine if either is associated with clinical outcomes. Biopsy specimens were reviewed using histologic criteria derived from grading schemes, and KIT antibody expression patterns used in canine tumors and surveys were sent to referring veterinarians for follow-up clinical data. Arabians were overrepresented relative to the reference population. Most tumors were well differentiated with low mitotic rates (96%), and aberrant KIT staining patterns, as described in dogs, were uncommonly identified (12%). Associated clinical disease was uncommon and no tumors exhibited malignant behavior. Overall, KIT staining pattern and histologic features were not associated with poor clinical outcome or abnormal tumor behavior.

Mast cell tumors in a llama (Lama glama)

A 9-year-old female llama (Lama glama) that served as a blood donor at The Ohio State University Veterinary Teaching Hospital developed multiple small, raised, firm, non-haired cutaneous masses on the right hip, left cheek, and right and left shoulders. Cytological evaluation of fine-needle aspirates from the cutaneous mass from the left shoulder and right hip comprised many well-differentiated, highly granulated mast cells with moderate numbers of eosinophils. Occasional mast cells exhibited erythrophagocytosis and contained a small amount of hemosiderin or several variably sized vacuoles. A cytologic diagnosis of mast cell tumor with evidence of prior hemorrhage was made, and the masses were surgically removed. Microscopically, each mass consisted of sheets of neoplastic round cells that formed nonencapsulated nodules in the dermis and infiltrated into the adjacent dermal collagen. Eosinophils were scattered among the mast cells at the periphery of the nodules. Neoplastic mast cells, but not eosinophils, exhibited positive membrane KIT expression and cytoplasmic vimentin staining. A final diagnosis of mast cell tumor was made based on cytology, histology, and immunohistochemistry.

Multicentric mast cell tumors in a horse

A 6-year-old female Rocky Mountain horse was presented for evaluation of draining tracts and distal limb subcutaneous edema on the left front and left hind limbs that had been present for 2 weeks. Direct smears of fluid collected by fine-needle aspiration of subcutaneous fluid from both limbs were highly cellular with a predominance of eosinophils accompanied by numerous, moderately atypical, variably granulated mast cells. The cytologic diagnosis was mast cell tumor (MCT) with prominent eosinophilic infiltration with a differential diagnosis of eosinophilic granuloma. Histologic evaluation of surgical biopsies of lesions from both limbs was performed on sections stained with H&E, toluidine blue, and Luna stains. The histologic diagnosis was MCT, and staining with toluidine blue and Luna stains confirmed the presence of mast cells and eosinophils, respectively. In addition, the mast cells strongly expressed CD117. This is the first reported case of cutaneous mast cell neoplasia in a horse in which primary presenting complaints were draining tracts and distal limb subcutaneous edema involving multiple limbs. This case illustrates the utility of staining for CD117 expression in combination with traditional stains, such as toluidine blue and Luna, in differentiating MCTs from other eosinophilic lesions in horses.