Vulvar squamous cell carcinoma in situ within viral papillomas in an aged Quarter Horse mare.

Summary This report describes the diagnosis and treatment of vulvar papillomatosis with carcinoma in situ in a 25-year-old mare. Papillomavirus was demonstrated via immunohistochemical staining of biopsies of the lesion. The papillomas were removed via laser excision and the surrounding vulvar tissue injected with 5-fluorouracil. Additional more extensive laser excisions were required due to recurrence.