Mast cell tumours (MCT) are a common neoplasm of dogs, but their behaviour is variable. Several breeds, including boxers and Boston terriers appear predisposed to MCT development. The clinical course for different breeds is less well documented.

Retrospective analysis of dogs presenting with MCT to a university teaching hospital (1997–2007) was carried out, looking for associations between breed and site and the presence of metastasis at presentation. The breeds presenting with MCT were also compared to a previously published database of 130,684 insured dogs in the UK.

Two-hundred and twenty-two dogs met the inclusion criteria: histological or cytological diagnosis of MCT and staging to include at least chest radiographs, abdominal ultrasound and local lymph node palpation/fine needle aspiration. Analysis was carried for breeds and sites with 5 or more cases.

Compared to the insurance population, Staffordshire bull terriers (SBT) (Odds Ratio 3.49; 95% Confidence Intervals 2.09–5.81), Labrador retrievers (OR 2.97, 95%CI 2.22–3.97), boxers (OR 2.44; 95% CI 1.57–3.80) and golden retrievers (OR 1.58; 95% CI 1.07–2.33) appeared overrepresented. German shepherd dogs (OR 0.13; 95% CI 0.04–0.42) and cocker spaniels (OR 0.20; 95% CI 0.05–0.82) were both underrepresented.

Fourty-four different breeds were represented in the dataset. Five breeds included more than 5 cases, which were Labradors (n = 66), golden retrievers (n = 29), boxers (n = 22), SBT (n = 16), and Jack Russell terriers (JRT) (n = 6); there were 23 cross breed dogs. Overall, at presentation, 18% had multiple tumours (n = 40), 30% had lymph node metastasis (n = 68), and 6.7% had distant metastasis (n = 15). Multiple tumours did not make metastasis more likely. Boxers appeared to be at lower risk of developing lymph node metastases (n = 1; OR 0.095; 95% CI 0.012–0.718). Golden retrievers were at increased risk of multiple tumours (n = 14; OR 5.96; 95% CI 2.58–13.8) but not of developing metastasis. Labradors appeared more prone to metastasis, although this was not statistically proven. Meaningful conclusions could not be drawn in JRT and SBT.

When site was considered, MCT on the head (n = 36) (excluding conjunctiva) appeared to be more likely to metastasise to the local lymph node (n = 17; OR 2.37; 95% CI 1.14–4.94) and distantly (n = 5; OR 3.93; 95% CI 1.31–11.9). 57% of tumours occurred on limbs (n = 126) but their site, including position on limb, did not significantly affect behaviour.