The histopathological subtyping and grading of oral squamous cell carcinoma are well established in human medicine, but there are currently no standard classification and grading schema used for oral squamous cell carcinoma in cats. In this study, it was aimed to investigate different subtypes and grades of feline oral squamous cell carcinoma and the possible role of the papillomavirus infection in the progression of this tumor by using the methods of histopathology, immunohistochemistry, and transmission electron microscopy. Out of the 32 tissue samples, conventional (14/31; 43.75%), verrucous (8/32; 25%), papillary (5/32; 15.62%), acantholytic (3/32; 9.37%), and adenosquamous (2/32; 6.25%) subtypes of the tumor were determined in the affected cats. Grading of the tumor was performed according to Anneroth's and Bryne's systems and revealed that there was no relationship between histopathological subtypes and grades of the cases. Histopathologic findings suggestive of papillomavirus infection were determined not only in verrucous and papillary subtypes as seen in human medicine, but also in different other subtypes of the tumor. Moreover, immunopositivity for papillomavirus was obtained from the conventional, acantholytic, and adenosquamous subtypes of the tumor. In conclusion, the relationship between grading and subtypes of oral squamous cell carcinoma observed in this study showed differences in comparison with the human counterparts. The effect of papillomavirus infection in the progression of oral squamous cell carcinoma remained uncertain
