Comparative Immunoreactivity of iNOS , PCNA and p53 in Stable and Progressive Canine Transmissible Venereal Tumours

Canine transmissible venereal tumour (CTVT) is a naturally occurring transmissible neoplasm with variable biological behaviour, including progressive growth, stationary behaviour and spontaneous regression. However, the marker-expression patterns associated with these clinicopathological phenotypes remain incompletely characterised. The present study investigated iNOS, PCNA and p53 expression in CTVT and evaluated their association with the operational clinicopathological phenotype. Sixteen genital CTVT samples obtained from surgically treated dogs were classified as stable (n = 7) or progressive (n = 9) using predefined criteria requiring concordance between local invasion and quantitative mitotic count. Immunohistochemistry was performed for iNOS, PCNA, p53 and cytokeratin (CK), and immunoreactivity was evaluated semiquantitatively by two blinded observers. Progressive tumours showed significantly higher iNOS, PCNA and p53 immunoreactivity scores than stable tumours. Across the three markers, median scores ranged from 0 to 1 in stable tumours and were 3 in progressive tumours, with significant differences in all comparisons (Mann-Whitney U = 0.0; two-sided exact p = 0.0002). iNOS immunoreactivity was predominantly cytoplasmic in tumour cells, with occasional staining in vascular endothelial and inflammatory cells, whereas PCNA and p53 showed widespread nuclear positivity in progressive tumours and more limited expression in stable tumours. CK immunoreactivity was absent in all samples, consistent with the absence of detectable cytokeratin expression in the examined tumours. To our knowledge, the present study provides the first tumour-cell-focused characterisation of iNOS immunoreactivity in CTVT, evaluated concurrently with PCNA and p53 across operationally defined stable and progressive clinicopathological phenotypes.