Supposed primary conjunctival lymphoma in a dog.

A 7-year-old, male mixed-breed dog was presented for evaluation of a well-delineated, pink, oval and slightly firm mass with a smooth regular surface that was expanding approximately 60% of the lower eyelid conjunctiva and the lateral canthus. The dog had a supposed primary B-cell lymphoma at the temporal canthus of the upper eyelid conjunctiva of the same eye that had been removed approximately 3 years earlier. No metastases were detected at either presentation. Histologically, the conjunctival lamina propria was effaced by a well-delineated, unencapsulated and expansile highly cellular neoplasm composed of sheets of round cells that were immunohistochemically positive for CD20 and CD79a negative for CD3. Based on the microscopic and immunohistochemical findings, a diagnosis of supposed primary B cell conjunctival lymphoma was made. Primary ocular and adnexal ocular lymphomas in dogs are rarely reported and their behavior is poorly characterized. Further tumor recurrence was not observed one year post operatively. This case was considered unusual because of its conjunctival involvement and the clinical course with recurrence after three years of a surgical therapeutic procedure.