A 25-year-old, female, South African fur seal (Arctocephalus pusillus pusillus), with an unremarkable medical history, developed a pigmented oral mass and skin nodules in the dorsal region (mainly cervico-thoracic). Skin nodules presented with different sizes, firm consistency and were very adherent to the subcutaneous tissue. Excisional surgery was performed and biopsies were taken.

After surgery the skin nodules showed an aggressive biological behaviour manifested by fast growth and soreness. Four months later the animal’s quality of life had deteriorated significantly and euthanasia was the most ethical option. All lesions observed during the necropsy suggested an advanced neoplastic disease with aggressive tumoral behavior which was likely the primary differential diagnosis. Histology and immunohistochemical studies (Melan-A, S-100, PNL-2) were consistent with a high grade malignant melanoma.

Remarkable histology findings in this case were the large number of neoplastic lesions expanding the serosal fibrovascular connective tissue of multiple organs.

The results of immunohistochemical studies did not confirm the cellular origin of the primary tumor, although the clinical history indicates the oral mass as the primary lesion.

To the authors’ knowledge this is the first report of cutaneous melanoma in Otariidae.

* Presenting author