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Xanthelasmoid mastocytosis or xanthelasmoidea is a rare clinical variant of cutaneous mastocytosis characterized by a yellow hue of the clinical lesions, which are often misdiagnosed as juvenile xanthogranuloma. We present two pediatric cases of xanthelasmoid mastocytosis presenting as isolated mastocytomas, which are notable histopathologically for their hypervascularity. This pseudoangiomatous variant of cutaneous mastocytosis is important for pathologists to have knowledge of, so that a diagnosis of a vascular tumor is not rendered accidentally. The yellow hue has previously been explained by the usual deep and solid dermal mast cell infiltrate. In the two presented cases, however, the mast cell infiltrate was sparse, and the yellow color cannot be related to infiltrate density. We believe that the hypervascularity is at least one factor in the production of clinical xanthelasmoid appearance, and we propose the term 'pseudoangiomatous xanthelasmoid mastocytosis' to properly describe this rare variant of cutaneous mastocytosis., (© 2015 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.)

Canine cutaneous mast cell tumor (MCT) is very common disease in dogs, this is more aggressive than in other species. The biologic behavior of MCT is highly variable and a more accurate prognosis for these tumors needs to performed. The proto-oncogene c-kit is known to play a critical role in development and function of mast cells (MC). The aim of this study was to evaluate the expression of immunohistochemical pattern of c-kit in MCTs and to correlate these results with MC density (MCD) and intratumoral microvessel density (MVD). Our results confirm that a more aggressive biologic behavior of canine MCT is associated with the increased c-kit expression, further suggesting a new role for c-kit, as a useful marker, in diagnostic pathology and in tumor progression.