Histopathological characteristics of five clinical types of equine sarcoid

The purpose of this study was to determine the characteristics of occult, verrucous, fibroblastic, nodular and mixed equine sarcoids. Ten tumours of each type were examined histologically and analysed for the presence of bovine papilloma virus (BPV)- DNA. All tumours were positive for BPV - DNA and showed an increased density of dermal fibroblasts. Epidermal hyperplasia, hyperkeratosis, rete peg and 'picket fence' formation were only found consistently in the verrucous and mixed types and were often not present in occult and nodular sarcoids. Immunohistochemical staining for Keratins 10 and 16, Ki67 and p53 showed no important differences between the clinical types. It can be concluded that the presence of BPV - DNA and the increased density of dermal fibroblasts were the only common characteristics for all sarcoids of the different clinical types. The presence of other microscopic alterations was variable but could not be used in the differentiation of the clinical types based on histology.