Evaluation of Cyclooxygenase-2 Expression in Canine Mast Cell Tumours

SummaryMast cell tumours (MCTs) are among the most common cutaneous neoplasms in dogs and have a highly variable clinical behaviour. Cyclooxygenase (Cox) catalyzes the rate-limiting step in prostanoid biosynthesis and has recently gained attention as a prognostic factor and therapeutic target in human and animal oncology. In order to evaluate the potential value of non-steroidal anti-inflammatory drugs (NSAIDs) in the treatment of canine MCTs, expression of Cox-2 was determined in 49 such tumours (14 of grade I, nine of grade II and 22 of grade III). Cox-2 was expressed by 86% of the tumours studied. The percentage of labelled cells ranged from isolated positive cells throughout the tumour (n = 8) to localized foci of labelled cells (n = 3) or diffuse labelling of >50% of the cells (n = 31). The intensity of Cox-2 labelling ranged from weak (n = 4) to moderate (n = 16) and strong (n = 22) and was greatest at the advancing margin of the tumour. The intensity of Cox-2 labelling was significantly different between the three histological groups (P = 0.018). However, no significant differences were noted for the percentage of Cox-2 positive cells (P = 0.122) and for the immunoreactivity score (P = 0.348) between the histological grades. The results of this study suggest that NSAIDs, particularly Cox-2 inhibitors, may be of value in the treatment of canine MCTs.