12/08/2026
🔬 CytoInsights: High-grade mast cell tumour in a dog
By Mario Cabezas-Calvo DVM, CSAVP
A cutaneous mass from a dog was submitted for cytological evaluation.
Cytology was highly cellular, composed predominantly of large round cells containing moderate to abundant purple cytoplasmic granules – characteristic features of mast cells. However, beyond identifying the tumour type, cytology also revealed several features suggestive of aggressive biological behaviour.
The mast cell population displayed marked atypia, including marked anisokaryosis, frequent mitotic figures, and numerous bi- and multinucleated cells. In some cases, marked variation in nuclear size was evident even within the same cell. These atypical features are important, as they have been associated with high-grade mast cell tumours.
Moderate numbers of eosinophils and neutrophils were also seen admixed with the neoplastic mast cell population. Eosinophilic inflammation is a common secondary finding in mast cell tumours and can provide an additional diagnostic clue, particularly in poorly granulated tumours where mast cells may be more difficult to recognise.
High-grade mast cell tumours are associated with more aggressive clinical behaviour, increased metastatic potential and shorter survival times compared with low-grade tumours.
Although definitive grading requires histopathological evaluation, cytology remains an essential first-line diagnostic tool. Early cytological assessment can help clinicians anticipate tumour behaviour, guide staging recommendations and support surgical and therapeutic planning.
🔬 Got a case you'd like to discuss?
Call our office to speak with one of our Clinical Pathologists.
