Malignant tumors, or tumors that will grow rapidly, invade and destroy adjacent tissues, and metastasize to distant sites where they can continue their destructive processes, are very rare in ferret skin. Basal tumors appear as small warty growths that may have a depressed centers. They grow slowly, and are freely movable, as they do not involve structures underneath the skin. They are most common on ferrets over the age of four. The second most common skin tumor in the ferret is the mast cell tumor.
Mast cells are a population of cells in the skin which are closely associated with blood cells.
Normally, they mediate allergic reactions, liberating certain chemicals which cause vascular dilation, causing the redness associated with hives and other allergic conditions. Mast cell tumors, although they are associated with a high rate of malignancy in the dog and cat, are generally benign in the ferret. There are no reports of malignant mast cell tumors in the ferret medical literature. Mast cell tumors usually appear as flat, often hairless, small plaques on the ferret's body. They are also freely movable and do not involve underlying structures.