Rectal mast cell tumour in a dog with lower grade features of biological aggressiveness

An 8-year-old, neutered female, Australian Silky Terrier presented to her primary veterinarian with non-specific clinical signs of general unwellness, shaking, lethargy, inappetence and no defecation for 2-3 days. A rectal mass was found on physical examination. The rectal mass was surgically resected and histopathology was consistent with a mast cell tumour (MCT) with a mitotic count of 0 per 2.37mm². The dog had follow-up chemotherapy protocol comprising of vinblastine and prednisolone and was doing well with no evidence of tumour recurrence 30 weeks post surgical resection and is still alive and clinically normal at the time of writing, 9 months post initial diagnosis. Primary MCTs of the gastrointestinal tract have previously been reported to be associated with a poor prognosis. This is the first report of a canine rectal mast cell tumour with lower grade features of biological aggressiveness and a possibly more favourable prognosis compared with the current published literature.