Effects of stage and number of tumours on prognosis of dogs with cutaneous mast cell tumours

Between 1997 and 1999, 280 dogs with mast cell tumours were identified, of which 59 (21 per cent) had multiple tumours. Follow-up data for survival analysis were available for 145 dogs with single tumours and 50 dogs with multiple tumours. There was no significant difference between the survival times of the two groups; the survival rates after 12 and 24 months were 88 per cent and 83 per cent, respectively, for the dogs with single tumours, and 86 per cent at both intervals for the dogs with multiple tumours. Eight of the dogs with single tumours had lymph node metastases (stage II disease) and these dogs had a median survival time of 431 days, whereas the 50 dogs with multiple tumours (classified as stage III disease) and the dogs with single tumours (classified as stage I disease) had not reached their median survival times. Golden retrievers appeared to be predisposed to developing multiple tumours in the population studied, with an odds ratio of 3.8. This study found no evidence that dogs with multiple tumours had different survival times than those with single tumours, although there was evidence that the presence of lymph node metastasis generally carried a poorer prognosis.