Bilateral pre-auricular papillary squamous cell carcinomas associated with papillomavirus infection in a domestic cat

Cutaneous papillary squamous cell carcinomas (SCCs) are extremely rare in humans and have not been reported in any nonhuman species. In humans, oral papillary SCCs are often caused by papillomavirus infection and have a more favourable prognosis than other SCC subtypes.

A 10-year-old ginger and white domestic short hair cat had a 12 month history of symmetrical, roughly circular, exophytic 2 cm diameter masses in both pre-auricular regions. Surgical excision was performed, although with only narrow margins.

Histology of both masses revealed a proliferation of neoplastic keratinocytes arranged in numerous filiform projections that were supported by fibrovascular stalks. Although the cells were confined to the epidermis predominantly, nests of neoplastic cells were visible within the superficial dermis. The neoplastic cells demonstrated significant atypia with a variable nuclear:cytoplasmic ratio and a high mitotic index. A papillary subtype SCC was diagnosed. Felis catus papillomavirus type 2 (FcaPV-2) was the only papillomavirus detected in the masses and FcaPV-2 E6/E7 gene expression and p16^CDKN2A protein immunostaining were detected. Six months after surgery neither recurrence nor further masses had developed.

This is the first cutaneous papillary SCC reported in a nonhuman species. Papillary SCCs may be a rare manifestation of FcaPV-2 infection in cats. The unusual location of the SCCs suggests that both papillomavirus infection and ultraviolet light exposure could have contributed to neoplasia development. Evidence from this single case suggests that papillary SCCs may have a more favourable prognosis than conventional SCCs in cats.