Conjunctival melanoma in a dog

A 7-year-old male neutered Border Terrier has undergone enulceation of his right eye for a melanoma involving the dorsal palpebral conjunctiva.

Fig 1. Enucleated specimen with attached eyelids. A poorly delineated pigmented tumour is present in the dorsal conjunctiva (blue arrow).
Fig 2. Sparsely pigmented neoplastic melanocytes. The blue arrows highlight the mitotic figures (H&E, x400).
Fig 3. Neoplastic melanocytes often proliferate and form nests within the epithelium (of either the skin or mucosal surface) at the epidermal-dermal or mucosal-stromal junction and this is known as junctional activity. This junctional activity often extends beyond the main clinically visible tumour and can make complete excision difficult. Neoplastic nonpigmented melanocytes form intraepithelial nests in this section of bulbar conjunctiva. (H&E, x 200)

Final Diagnosis

Malignant conjunctival melanoma


The majority of conjunctival melanomas in the dog are histopathologically malignant and therefore carry a risk of post-surgical recurrence and metastasis. This is in contrast to melanocytic tumours arising in the skin (including the eyelid), the majority of which are benign in the dog. Following excision of conjunctival melanomas, additional tumours may also sometimes arise in the near vicinity of the surgical site which are presumably satellite lesions arising via lymphatic spread. Conjunctival melanomas in dogs most commonly affect the third eyelid but the palpebral and bulbar conjunctiva can also be involved such as in this case.