Cutaneous Mast Cell Tumor With Metastasis in a Pet Cairo Spiny Mouse (Acomys cahirinus): A Case Report With Clinicopathologic Characterization.

A 3-year-old male pet Cario spiny mouse (Acomys cahirinus) presented with an exophytic, sessile dermal mass at the base of the left ear. Histopathological examination of the excisional biopsy revealed a poorly demarcated, densely cellular neoplasm composed of sheets of round to polygonal cells containing variably distinct basophilic to amphophilic fine intracytoplasmic granules. The granules exhibited metachromasia with toluidine blue and Giemsa stains. Neoplastic cells were immunopositive for c-kit (CD117) and tryptase, confirming a diagnosis of mast cell tumor (MCT). The tumor was narrowly excised, and the mouse remained clinically well 1 month postsurgery without evidence of recurrence; however, the mouse declined clinically with tumor recurrence and was euthanized at 3 months postsurgery. Necropsy revealed local recurrence with metastasis to regional lymph nodes and spleen. This case report represents, to the authors' knowledge, the first report of a cutaneous MCT in a Cario spiny mouse and demonstrates malignant biological behavior. This report highlights the importance of considering MCTs in the differential diagnosis of cutaneous masses in exotic rodents.