T cell-lymphoma in the eyelid of a 9-year-old English Setter

a A 9-year-old male English Setter presented with a 6-month history of an eyelid ulcer on top of a tumour measuring 10？×？14 mm. The lesion is round and surrounds a central area of normal eyelid epithelium with hair. b In overview, a diffuse infiltrate of lymphoid tumour cells is seen within the epidermis and dermis (#). A large ulceration of the epithelium is seen (arrow). The tumour cells fill the rete ridges (*) and invasion of the epithelium is seen in some areas. Invasion of the adnexal epithelium does not occur (haematoxylin and eosin (HE); bar: 100 μm). c The tumour cells have pale cytoplasm and prominent nucleoli. Numerous mitotic figures are seen (arrow). (HE; bar: 30 μm). d The tumour cells stain positive in anti-CD3 staining, indicating that the tumour cells are of T-cell origin (bar: 50 μm