Immunohistochemical expression of Mdm2 and p53 in canine cutaneous mast cell tumours

The objective of this study was to evaluate by immunohistochemical means nuclear reactivity for Mdm2 and p53 proteins in 71 canine cutaneous mast cell tumours. Detectable reactivity for Mdm2 was observed in 17 of 23 grade I tumours, 19 of 27 grade II tumours, and 14 of 21 grade III tumours, the grading method used was that by Patnaik et al. [Vet. Pathol., vol. 21, 1984, p. 469]. Increased reactivity for Mdm2 was detected in grade III tumours compared with grade I tumours. In contrast to Mdm2, detectable reactivity for p53 was observed in 17 tumours. Of 39 cases with moderate or marked Mdm2, 34 showed mild or no detectable p53, although only five showed moderate or marked p53. The results suggest that Mdm2 overexpression plays a crucial role in canine mast cell tumorigenesis and is consistent with the histologic grade, and its expression may be induced without p53 overexpression.