Malignant melanomas in a Duroc boar.

A Duroc boar had 2 malignant melanomas of the skin, with metastases into several lymph nodes, lungs, liver, and spleen. All tumors had these characteristics: invasion of lymph and blood vessels, necrosis, numerous giant cells containing granules, heavily pigmented as well as lightly pigmented and unpigmented melanocytes, few anaplastic features, and few mitotic figures. In the skin tumors, there was neither intraepithelial growth nor junctional activity.