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Mast cell tumours in dogs less than 12 months of age: a multi-institutional retrospective study.

OBJECTIVES
To describe the clinicopathological and genetic characteristics of mast cell tumours in dogs less than 12 months old.


MATERIALS AND METHODS
Retrospective review of dogs aged less than 12 months when diagnosed with mast cell tumours at three referral hospitals in the UK.


RESULTS
Sixteen pure-bred dogs were included, of which 11 were female. The median age at first presentation and diagnosis were 7.6 and 9 months, respectively. In 13 dogs the mast cell tumours were cutaneous and in three they were subcutaneous. Four cutaneous mast cell tumours were described as high-grade (Patnaik or Kiupel) and nine were Patnaik grade II; three had mitotic index of >5 in 10 high-power fields. Of the three subcutaneous tumours, two had an infiltrative growth pattern and one had mitotic index of 10 per 10 high-power fields. Of 10 tested dogs, seven had c-kit mutations in exon 11 and Ki-67 score was above the cut-off value in nine. Four of 12 cases showed evidence of metastasis in the regional lymph nodes. After varying treatment protocols, all patients were alive and disease free at a median of 1115 days after diagnosis.


CLINICAL SIGNIFICANCE
The prognosis of mast cell tumours in dogs less than a year old appears better than the adult counterparts, even without extensive treatment.