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Skin tumors are serious business

Stephen Sheldon, DVM

Skin tumors in our pets are a serious subject. Here are answers to some common questions. If you have questions always. call your veterinarian.

Q: Should I worry if I see a lump on my cat?

A: Yes, a little. Skin tumors represent the largest class of cancers in animals. The skin is the largest organ system and is exposed to a large number of environmental carcinogens and UV radiation. The news for cats is worse than it is for dogs: Most skin tumors in cats are malignant or cancerous; the opposite is true for dogs.



Skin tumors occur most often in our older cats; most feline cancer patients are 10 years or older. You will likely notice the tumor first and bring it to your veterinarians’ attention. Do not let him or her tell you to just watch it. All skin masses in cats deserve serious attention.

Q: Which tumor types are more common in cats?



A: Basal cell tumors are usually benign tumors of the epidermis, hair follicles, sweat or sebaceous glands. They are often found around the head and neck. This is the most common skin tumor and they rarely metastasize, or spread. Treatment is with adequate surgical removal. If the lesion is not completely removed, radiation therapy may be recommended. If the tumor comes back from the pathologist with a malignant grade a chest radiograph is indicated to check for metastasis. Chemotherapy may or may not be recommended if it is thought the cancer has spread. Fortunately, most of them are not malignant and the old saying “a chance to cut is a chance to cure” applies well here.

Squamous cell carcinomas occur most commonly around the head, as well. Most of them are found around the ears, nose and eyelids in cats who lack pigment in these areas. And, as you probably guessed, they are induced by sunlight. Interestingly, Siamese cats, who have an abundance of facial pigmentation, are less likely to develop SCCs, which have a rather distinct presentation. Initially the area becomes red and may have a waxy, dark, crusty appearance. If left untreated, they progress and start to ulcerate and destroy surrounding tissue. Most of them do not metastasize until later in the course of the disease, commonly spreading to the regional lymph nodes, lungs, and bone.

Treatment of SCC is by either surgery, radiation therapy or cryotherapy (freezing). However, a 1991 study by Atwater, Withrow, et al, found cryotherapy was considerably less effective than surgery or radiation and should not be used in tumors larger than 1 centimeter. The prognosis for reoccurrence is determined by two things: size of the tumor; and location. Smaller tumors behave much better than larger tumors, and those that involve the tongue or bones of the jaw have a worse prognosis.



Other therapies used with some success in SCCs are intralesional injection of the tumor with cisplatin and photodynamic therapy. Interestingly, cisplatin is deadly to cats if given the usual intravenous route, but is well tolerated if injected into the tumor.

The next tumor, fibrosarcoma, can account for up to 25 percent of feline tumors. These tumors can occur in cats infected with the feline leukemia or sarcoma viruses. However, most fibrosarcomas in older cats are not associated with either of these viruses. The limbs are the most common sites of these tumors. They can get quite big and may ulcerate. The metastatic rate is low but they can spread to the lungs through the blood. The problem with fibrosarcomas and other soft tissue sarcomas is they recur locally.

Fibrosarcomas and other sarcomas are best treated with wide, deep, and early surgical excision. A surgeons’ best chance to cure these tumors is the first surgery. These tumors send microscopic, finger-like projections into surrounding tissue, therefore making complete excision difficult. This is one reason a pre-op biopsy is strongly recommended if fibrosarcoma is suspected. Radiation therapy is a very useful adjunct in treating incompletely excised tumors. It can also be used as a measure of caution in completely excised tumors. Chemotherapy for incompletely excised tumors or to slow metastasis has yet to be fully evaluated. There are reports of various successes using doxorubicin, vincristine and mitoxantrone. Make sure you seek a veterinarian who is familiar with chemotherapy; most who are not will be glad to refer you to someone who is.

Q: I’ve heard vaccinating my cat can cause tumors. Is that true?

A: What we’re about to discuss next should be handled with care. There is a small risk – about one in 10,000 – of developing a fibrosarcoma as a result of being given the feline leukemia vaccine. Some researches postulated it was due to an aluminum adjuvant in the vaccine and they have since been removed by the vaccine manufacturers.

The American Association of Feline Practitioners has recommended using specific sites on a cats body for specific vaccines; this they hope will lessen the incidence of vaccine related tumors. Also, vaccines often are given in the same site.

I want to point out that, by far, most fibrosarcomas are not associated with vaccines and the risk of contracting a deadly virus greatly outweighs the small possibility of developing a tumor.

Among other common skin tumors in cats are mast cell tumors. MCTs can be solitary and compact or diffuse and invasive; they divide up about 50/50 into these two categories. Surgery is the treatment of choice, followed by either radiation or chemotherapy for incompletely excised tumors. We use either prednisone or mitoxantrone. Melanomas occur quite infrequently in cats in the skin; more often they show up in the oral cavity where they are serious. Lipomas are benign tumors of fat or adipose cells and are very rare in cats. They are very easy to diagnose with a fine needle biopsy and should be removed as other tumors can mimic lipomas.

Q: What should I do if I see a lump on my cat?

A: You know the first thing to do already – seek veterinary help as soon as possible. Your veterinarian may perform a fine needle biopsy right away or schedule an excisional biopsy, wedge biopsy or complete removal. A biopsy should be done if it will change the way a surgeon would remove the mass or if it would change the way an owner would treat the pet. To quote Dr. Greg Ogilve from CSU, “surgery has always been the most effective treatment for malignancies in cats”.

One last rule of oncology: “if it’s worth taking out, it’s worth sending out,” meaning if you have a lump removed make sure your veterinarian sends it out to a pathologist to find out what type of tumor it is. Does it cost a little extra? Yes. Is it necessary? Absolutely.

Editor’s note: Dr. Stephen Sheldon, owner of Valley Veterinary Services, practices by appointment at Alpine Meadows Veterinary Hospital in Edwards. He can be reached at 970-748-3062.


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