Statement from the Authors In preparing this document the Authors aimed to pool current information on canine and feline mast cell disease. The information was gathered from international studies and a emphasis was placed on material and opinion with a strong evidence base. We intend it to form the basis of our understanding in this disease at the current time and we anticipate that it will be particularly useful for the general practitioner. It should be emphasized that the authors are presenting this work from a European perspective.

The histological grade of 340 cutaneous mast cell tumours derived from 280 dogs was determined by an established histological grading system; 87 of the tumours (26 per cent) were well differentiated, 199 (59 per cent) were intermediately differentiated and 54 (16 per cent) were poorly differentiated. The one-year survival rates for the dogs with tumours of these three grades were significantly different (P = 0.0001), being 100 per cent, 92 per cent and 46 per cent, respectively. The median survival time for the dogs with poorly differentiated tumours was 278 days, significantly shorter than that for the dogs with either intermediately or well-differentiated tumours, which were both over 1300 days. Regrowth of the tumours was identified in 10 (19 per cent) of the dogs with poorly differentiated tumours, 12 (6 per cent) of the dogs with intermediately differentiated tumours and one of the dogs with well-differentiated tumours; only three of the tumours which regrew had initially had complete margins. The results suggest that wide surgical margins are not a prerequisite for a successful long-term outcome in dogs with well-differentiated 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.

The Patnaik histologic grading system is commonly used to predict the behavior of cutaneous mast cell tumors (MCTs) in dogs, but it is less useful for grade 2 MCTs because they exhibit considerable variation in biological behavior. In this retrospective study, immunohistochemical staining for Ki-67, proliferating cell nuclear antigen (PCNA), and survivin and a standardized argyrophilic staining of nucleolar organizer regions (AgNOR) protocol were performed on 121 archived paraffin-embedded specimens of canine cutaneous MCTs, for which clinical follow-up data were available. Cox regression models indicated that the Ki-67 score (hazard ratio, 1.92; P , .001) and mean AgNOR score (hazard ratio, 2.57; P , .001) were significantly associated with Patnaik grade and survival time. A binary Ki-67 variable (cutoff point Ki-67 score 5 1.8) was a significant predictor of survival for dogs with grade 2 MCTs. The estimated 1-, 2-, and 3-year survival probabilities for dogs with grade 2 MCTs and Ki-67 scores less than 1.8 were 0.92, 0.86, and 0.77, respectively (SEs, 0.08, 0.14, and 0.23, respectively; median not estimable). The corresponding survival probabilities for dogs with grade 2 MCTs and Ki-67 scores higher than 1.8 were 0. 43, 0.21, and 0.21, respectively (SEs, 0.19, 0.18, and 0.18, respectively; median survival time, 395 days). No significant association was identified between survival and survivin score or PCNA score. This study shows that both mean AgNOR score and Ki-67 score are prognostic markers for canine MCTs. The Ki-67 score can be used to divide Patnaik grade 2 MCTs into 2 groups with markedly different expected survival times.

The Patnaik histologic grading system is commonly used to predict the behavior of cutaneous mast cell tumors (MCTs) in dogs, but it is less useful for grade 2 MCTs because they exhibit considerable variation in biological behavior. In this retrospective study, immunohistochemical staining for Ki-67, proliferating cell nuclear antigen (PCNA), and survivin and a standardized argyrophilic staining of nucleolar organizer regions (AgNOR) protocol were performed on 121 archived paraffin-embedded specimens of canine cutaneous MCTs, for which clinical follow-up data were available. Cox regression models indicated that the Ki-67 score (hazard ratio, 1.92; P , .001) and mean AgNOR score (hazard ratio, 2.57; P , .001) were significantly associated with Patnaik grade and survival time. A binary Ki-67 variable (cutoff point Ki-67 score 5 1.8) was a significant predictor of survival for dogs with grade 2 MCTs. The estimated 1-, 2-, and 3-year survival probabilities for dogs with grade 2 MCTs and Ki-67 scores less than 1.8 were 0.92, 0.86, and 0.77, respectively (SEs, 0.08, 0.14, and 0.23, respectively; median not estimable). The corresponding survival probabilities for dogs with grade 2 MCTs and Ki-67 scores higher than 1.8 were 0.43, 0.21, and 0.21, respectively (SEs, 0.19, 0.18, and 0.18, respectively; median survival time, 395 days). No significant association was identified between survival and survivin score or PCNA score. This study shows that both mean AgNOR score and Ki-67 score are prognostic markers for canine MCTs. The Ki-67 score can be used to divide Patnaik grade 2 MCTs into 2 groups with markedly different expected survival times.