Immunoreactivity of p21, MMP-1 and CB2 receptor proteins in cutaneous canine mast cell tumours: an association with the three-tier grading system.

Introduction: Mast cell tumours (MCTs) arise in the dermis and subcutaneous tissues in animals and humans and are one of the most common neoplasms of the skin in dogs. Cannabinoid type 2 receptor (CB2R), cyclin-dependent kinase inhibitor (p21) and matrix metalloproteinase 1 (MMP-1) are potential targets for novel anti-tumour therapeutic strategies. This study evaluated by immunohistochemical means the reactivity of p21, MMP-1 and CB2R proteins in association with a three-tier grading system in cutaneous canine MCTs.

Material and methods: Formalin-fixed, paraffin-embedded canine MCTs were processed for histochemical analysis and immunohistochemical staining using antibodies against p21, MMP-1 and CB2R. The results were analysed statistically.

Results: The strongest p21 immunolabelling was detected in grade 3 MCTs, while grade 1 tumours showed mild or no detectable p21 immunoreactivity (P-value < 0.001). Strong immunolabelling of MMP-1 was the most common in grade 1 tumours (P-value < 0.001) and CB2R was significantly less frequent in grade 3 tumours than in grade 1 (P-value < 0.001) and grade 2 (P-value < 0.001).

Conclusion: High immunoreactivity of MMP-1 can be a marker of grade 1 MCTs in dogs, whereas p21 protein overexpression can be a marker of grade 3 canine MCTs. Strong CB2R immunoreactivity with simultaneous underexpression of p21 and high immunoreactivity of MMP-1 proteins may indicate that the use of cannabinoids in grade 1 MCTs in dogs is practicable.