Ki67 Labelling Index of Neoplastic Epithelial Cells Differentiates Canine Acanthomatous Ameloblastoma from Oral...

Canine acanthomatous ameloblastoma (CAA) and oral squamous cell carcinoma (OSCC) are the most common oral tumours of epithelial origin in dogs. Overlapping clinical, radiographical and histological features can make distinction between CAA and OSCC difficult. The ability to distinguish tumour identity is critical due to their different biological behaviour and recommended treatment modalities, as well as respective comparative and translational applications as potential models of human disease. Based on marked differences in biological behaviour (i.e. benign versus malignant), it is reasonable to predict that the tumour cell proliferation activity is lower in CAA than in OSCC. However, to our knowledge, the epithelial cell proliferation activity of CAA has not been studied or compared with that of OSCC. Therefore, the aims of this study were to (1) compare the neoplastic epithelial cell proliferation activity of CAA and OSCC based on conventional mitotic index (MI) and Ki67 labelling index (LI), and (2) correlate these findings with clinical parameters including patient signalment, anatomical tumour location and degree of local invasion at the time of diagnosis as determined by computed tomography. We found that (1) the Ki67 LI of OSSC (n = 14) was significantly higher than that of CAA (n = 25), (2) the Ki67 LI correlated with a more aggressive locally invasive behaviour, and (3) the MI was not associated with tumour type. We conclude that the Ki67 LI, but not the MI, is a useful differential marker of CAA from OSCC, and that the epithelial cell proliferation activities of OSCC and CAA correlate with their known differences in biological behaviour.