Mast cell tumors can be malignant in most animals, but a mast cell tumor in ferrets is usually benign.
Mast cells are cells of the immune system which produce histamine. Mast cell tumors consist of an accumulation of mast cells. In ferrets, these tumors appear as slightly raised, sometimes reddish and usually hairless aberrations on the skin. They are on the surface of the skin and can be as large as ½ inch.
Since mast cells can release histamines they may become irritating to your ferret. He may scratch or chew at the tumors which can cause them to appear crusty or scabby. The histamines can cause hair loss. In rare cases, ferrets may have multiple tumors in any area.
Although benign, there have been some ferret deaths due to mast cell tumors reported so these (or any skin abnormality) on your ferret should not be checked out by your vet as soon as you can get your pet in for an appointment.
Tumors are not uncommon in ferrets and will become more frequent as your pet ages, but they should not be ignored. Many are not threatening to your pets health, but they can be irritating and, of course, you will never know for sure if it is cancerous unless you have it removed and analyzed.
If you suspect your ferret has a tumor, get him to a vet right away so a proper diagnosis can be made. In most cases, your vet will recommend removal of the tumor which usually solves the problem. It is not unusual, however, for a ferret that has had these to grow new ones at different sites.