Congenital neoplasms are common in large animals. Mastocytosis, melanocytosis, cutaneous lymphosarcoma, and vascular hamartomas are found in calves. Melanocytomas may also arise shortly after birth in calves and may be hereditary. These are thought to be benign.
Melanomas are seen in Duroc-Jersey and Sinclair miniature pigs as familial traits. These may undergo spontaneous remission or may behave as malignant tumors. Piglets have also been described with vascular hamartomas and with congenital fibropapillomatosis, which is likely infectious.
Congenital tumors are rare in dogs and cats. One dog with a giant congenital pigmented nevus had a malignant melanoma develop within the lesion. In cats, familial benign mastocytosis is described in young Siamese cats.
A syndrome of multiple collagenous nevi is seen in some families of German Shepherds and is called nodular dermatofibrosis. Affected dogs are adults. Dozens of skin lesions may occur, and those on the feet often ulcerate or cause foot deformities and lameness. This syndrome is a cutaneous marker for renal cystadenocarcinoma and uterine leiomyoma. Progressive dermal collagenosis is a similar disease of postpubertal male miniature pigs. It is thought to be hereditary and is characterized by symmetric, firm plaques on the trunk that consist of thick bundles of collagen replacing the normal dermis and panniculus. A connection with internal malignancy has not been reported.
Urticaria pigmentosa is caused by mast cell hyperplasia and has been described in cats. Affected cats have multifocal, partially coalescing macular and crusted papular eruption on the head, neck, and legs. Diagnosis is made by skin biopsy. There is evidence of a familial history.