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

Abstract

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.

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

“…Mast cell tumours comprise 3.4% of all cutaneous equine tumours, at least in the Pacific Northwest of the USA (Valentine, 2006). Equine MCTs appear most frequently on the head as a single nodule; multiple lesions are not indicative of malignant disease and may occur in any anatomical area of the skin (Ressel, Ward, & Kipar, 2015). Arabian horses appear to be more at risk compared to other breeds but no sex predilection has been described (Mair & Krudewig, 2008;Ressel et al, 2015).…”

“…Equine MCTs appear most frequently on the head as a single nodule; multiple lesions are not indicative of malignant disease and may occur in any anatomical area of the skin (Ressel, Ward, & Kipar, 2015). Arabian horses appear to be more at risk compared to other breeds but no sex predilection has been described (Mair & Krudewig, 2008;Ressel et al, 2015). Similar to MCTs in ferrets, equine MCTs follow a benign disease course and appear histologically well differentiated with a low mitotic rate.…”

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

“…Sections from the lungs and trachea were also stained by IH for cytokeratins (clone PCK-26; Novus Biologicals) to highlight respiratory and epithelial cells, for cleaved caspase-3 (rabbit anti-human cleaved caspase-3 monoclonal antibody; Asp175; clone 5A1E; Cell Signaling Technology) to demonstrate apoptotic cells, and for proliferating cell nuclear antigen (mouse anti-rat PCNA; clone PC10; Dako) to detect proliferating cells, using routine protocols established for other species (70)(71)(72). Intestinal epithelium was used as a positive control for all three detection systems after the cross-reactivity of the antibodies was confirmed by a comparison of the expression pattern in the python with those seen in the respective mammalian tissues.…”

Treatment of an invasive equine mast cell tumour in the extensor carpi radialis by extensive tenomyectomy and local corticosteroid injections

“…; Ressell et al . ). Although KIT expression was not assessed in this case, the invasive behaviour and clinical signs of pruritus, diffuse painful swelling and sudden onset of rapid growth were suggestive of malignancy.…”