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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 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 centers. 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 underlying 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
Dr. Williams is available to help with diagnoses and answer questions.
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, 1993.
2. Fox, JL. Biology and Diseases of the Ferret. Lea and Febiger, Philadelphia, 1988.
Mast cell tumors are seen in a variety of species of animals including dogs, cats, cattle, horses, and man. Mast cell tumors go under a number of names, all meaning the same condition: mastocytoma, mastocytosis, mast cell sarcoma. Mast cells are a type of cell that are associated with the immune system and are found throughout the body in a variety of areas such as bone marrow, lymphoid organs, connective tissue and under the lining (mucosa) of the respiratory and gastrointestinal tract. Mast cells are active participants in immune reactions against foreign substances. Within the cell body are granules which contain chemical substances such as histamine, serotonin, prostaglandins and others that create local inflammation which helps to destroy the foreign substance that has entered the body.
The cause of mast cells growing abnormally and creating a tumor is unknown in the ferret. It is an extremely common skin cancer in ferrets particularly in those animals three years of age and older. The appearance is usually that of a raised button-like lesion that is flat on top. The size may range from as little as 1/8 inch to over 1 inch. A few cases show as a diffuse raised red area that may be larger than one inch in diameter. The size may even change, and some small tumors seem to disappear temporarily. Because of the release of histamine from these cells, which can cause intense itching, some tumors have an ulcerated or raw appearance to their surfaces. Mast cell tumors can be found anywhere on the ferret's body but most typically on the trunk. They are also found on the toes, eyelids and tail. Although they are usually benign (meaning that they do not spread to other organs in the body) in the ferret, on occasion we have seen a malignant form that metastasizes to the spleen, liver or lung. The tumors usually occur in groups of one to three on the body.
The treatment is to remove the tumor or tumors surgically as soon as possible to prevent the possibility of metastasis. Surgery is fastest when the tumor is small. We use electrosurgery which has proven to be a fast and effective way to remove them. We recommend that skin tumors be sent to a pathologist, because even though it may look like a mast cell tumor, we cannot know for sure until it is examined microscopically. Microscopic examination will also give us a clue as to whether the tumor is benign or malignant, and what further treatment might be necessary for your pet. I have not yet seen a mast cell tumor return in the place where it was removed.
I recommend as a general rule that lumps and bumps on ferrets be removed promptly because they are so prone to cancers of all types, and why take a chance! I recommend taking you buddies to the veterinarian at least every 6 months after the age of 3 to keep ahead of all the possible problems that they may have.
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