Mast cell tumors in a long-tailed chinchilla (Chinchilla lanigera)

Background Mast cell tumors (MCT) have not previously been reported in pet long-tailed chinchillas ( Chinchilla lanigera ). Case description A 16-year-old spayed female chinchilla presented for lethargy, hyporexia, and a cutaneous mass. Upon physical examination, an alopecic cutaneous mass on the ventral thorax was noted. Cytology of fine needle aspirates followed by excisional biopsy with histopathology revealed a poorly granulated cutaneous MCT. The chinchilla represented 96 days post-operatively with multiple additional integumentary masses, and cytology of these masses was also consistent with MCTs. Given the presence of multiple MCTs and anticipated incomplete surgical margins, adjunctive toceranib was initiated as part of a palliative care plan at 1.25 mg/kg orally every other day the first week, followed by 1.9 mg/kg the second week, and 2.5 mg/kg starting the third week. At a follow-up two weeks after initiation of toceranib, while previously characterized MCTs had not decreased in size, no other overt new masses were noted, and toceranib appeared to be well-tolerated. However, by day 86 after treatment initiation (day 197 post-operatively), the chinchilla developed increasing discomfort attributed to the progression of mast cell disease, and humane euthanasia was elected. Postmortem examination revealed peripheral lymph node and visceral organ metastases. Conclusions and clinical relevance This case report is significant as neoplasia is rarely seen in chinchillas. While toceranib did not result in measurable tumor reduction in this case, it did appear to be well tolerated. Further information in a larger number of cases is needed to determine the efficacy of toceranib in chinchillas.