In previous articles, we have discussed
the two most common neoplasms of the ferret, islet cell tumors
[insulinomas] and adrenal tumors. Now lets look at the third
most common group, the various tumors of the skin.
Ferret skin tumors are very common, and
increase in frequency with age. Let's get one point straight
right away - the VAST majority of skin tumors in ferrets are
benign. 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.
The most common skin tumor in ferrets,
both at the AFIP [Armed Forces Institute of Pathology]
and in a recent retrospective study by Parker et al (Veterinary
Pathology, Jan 1994) is a tumor composed of undifferentiated
epithelial cells, known as a basal cell tumor. This cell has
the ability to differentiate into several different components
of normal skin, including glands (at which time it is called
a sebaceous epithelioma), hair follicles, or just simple sheets
of epidermal cells.
Most tumors show at least two, if not more
of these structures, a feature which has caused some pathologists
in the past to consider them malignant; however, now we know
that this is not the case.
Basal tumors appear as small warty growths
that may have a depressed center. They grow slowly, and are
freely movable, as they do not involve structures underneath
the skin. They are easily removed, and do not recur (unless
the surgeon fails to remove all of the tumor at the time of
surgery. They are most common on ferrets over the age of four.
While they should be removed, as they may become traumatized
and infected, owners should be reassured by the good outlook
(or prognosis) with which they are associated.
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 under-lying structures.
They may be somewhat crusty, as ferrets will often chew or
scratch at these sites, as some of these tumors itch. In rare
cases, animals may have multiple mast cell tumors at once.
Excision of these tumors is considered curative.
Another very common skin tumor is not actually
a tumor, but a cyst, or a dilated sweat gland, known as an
apocrine cyst. Apocrine glands may also form benign, or rarely,
malignant tumors, but by far, the most common lesion associated
with these glands is a simple cyst. These cysts appear as
small, round, hard "bubbles" just underneath the skin surface.
If squeezed, they may rupture and spill their contents into
the surrounding tissue. This causes a marked inflammatory
response and gives the appearance of rapid growth. Once again,
surgical excision is curative. These cysts may occur anywhere
on the body, but the prepuce, or penile sheath of males, is
the most common site, in my experience. There is a higher
concentration of apocrine glands here that at anywhere else
in the ferrets skin, so, logically, there would be an increased
incidence of cysts at this site as well.
Well, then, where are the bad tumors? There
are actually very few of them. In the last three years, I
have seen less than five. All of these skin tumors arose from
those apocrine sweat glands that we just talked about. This
malignant tumor, or carcinoma, generally grows rapidly, and
in contrast to most other skin tumors, often becomes firmly
anchored to underlying muscle. It rapidly invades and destroys
adjacent skin and may metastasize to the local lymph nodes,
or in the case of two the five cases, the lungs, resulting
in the death of the animal. While excision may be curative
if caught early, masses of this type that have reached any
size are associated with a much poorer outlook.
Of course, malignant tumors arising internally,
such as lymphosarcoma, may metastasize to the skin, as they
may metastasize to any other site. I have not discussed these
neoplasms, as they are generally uncommon and do not originate
in the skin.
One final note - while excision of the
vast majority of the tumors that we have discussed is curative,
there is nothing to prevent a second basal cell tumor, or
mast cell tumor, from arising in another site at a later date.
This does not worsen the prognosis for that animal, just requires
a second trip to the vet for removal. And remember, always
have your vet get those tumors analyzed - while most skin
tumors are benign, you and your pet will sleep better knowing
about that tumor for sure.
Bruce Williams, DVM
May not be altered or changed in any way.
Under Title 17 of the U.S. Code, Section 105, copyright protection
is not available for any work of the United States Government.
1. Parker, GA et al. Histopathogic features
and post-surgical sequelae of 57 cutaneous neoplasms in ferrets
(Mustela putorius furo). Veterinary Pathology, 30(6) 499-504,
2. Fox, JL. Biology and Diseases of the
Ferret. Lea and Febiger, Philadelphia, 1988.