A Case of Poorly Differentiated Cutaneous Canine Mast Cell Tumor with an Atypical Dermatologic Presentation

Abstract

Canine cutaneous mast cell tumors occur as nodular dermal lesions. A condition of mastocytosis is also described in dogs. The purpose of this study is to report the clinical and histopathological findings in a dog with high grade non-nodular cutaneous mast cell tumor. An 11-year-old intact male German Shepherd dog presented a severe erythematous dermatitis and erythematous plaques on the left thoracic wall, rapidly increasing in thickness, ulcerating, and spreading to the head. The fine needle cytology was indicative of a round cell neoplasm. The histological appearance of the lesions was suggestive of a high grade cutaneous mast cell tumor. Neoplastic cells were immunoistochemically Tryptase positive and c-kit positive (focal cytoplasmic staining), with a high Ki67 index. On the basis of this report high grade canine cutaneous mast cell tumors may show an atypical non-nodular presentation and should be included in the differential diagnosis for different lesions grossly appearing as erythematous dermatitis/plaques.