Histological subtypes of oral non-tonsillar squamous cell carcinoma in dogs.

Several histological subtypes and grades of oral squamous cell carcinoma (SCC) are described in human literature and these subtypes have distinct morphological features and biological behaviour. This retrospective study (1990-2010) included 84 dogs diagnosed with SCC of the oral cavity and oropharynx, excluding the tonsils. Sixty-nine of the SCCs (82.1%) were further diagnosed as conventional SCC (CSCC) (33 [47.8%] well-differentiated, 31 [44.9%] moderately-differentiated and five [7.3%] poorly-differentiated), five (5.95%) each as papillary SCC and basaloid SCC, three (3.6%) as adenosquamous carcinoma and two (2.4%) as spindle cell carcinoma. Compared with the general hospital population, neutered female dogs, dogs aged 10 to <15 years, English springer spaniels and Shetland sheepdogs were overrepresented. The majority (78.1%) of SCCs were proliferative with or without associated ulceration, although no significant association was observed between the gross appearance and different SCC subtypes. 71.4% of SCCs were located in dentate jaws; however, well-differentiated CSCC more often affected the tongue and other non-dentate mucosal surfaces (P=0.0022). No significant association was found between any of the SCC subtypes and tumour-associated inflammation (TAI), perineural and lymphovascular invasion (PNI, LVI), or between gross appearance of the tumour and tumour location, PNI, LVI or TAI or PNI, LVI, TAI and tumour location.