Ron Hines DVM Ph.D 4/24/06

Introduction:
We all know that older cats like older people are more susceptible to cancer. Until about fifteen years ago, the tumors we saw in cats were quite similar to the tumors we see in people, both in their types and in the age at which they occurred. But in the late 1980’s, veterinarians began to see a strange tumor occurring on the trunk of cats at much too young an age. Pathologist, reporting on these tumors, found that all were a highly malignant tumor of the connective tissue called fibrosarcomas or just sarcomas. These tumors spread slowly and could usually be removed (excised) - but they had a tendency to reoccur. In 25-30% of the cases the tumor eventually moved (metastasized) to other areas of the body – particularly the lungs. The original outbreak was along the North Atlantic coast of the United States. Several astute veterinary pathologists who were sent samples from these patients noticed that the tumors were occurring in areas of the body where cats had received vaccinations for rabies or feline leukemia. Approximately one in 10,000 cats developed these post-vaccination tumor. Several years before the tumor’s appearance, there had been an outbreak of rabies in raccoons in this area as well as an increase in feline leukemia cases. These two outbreaks caused more cats than usual to receive annual booster vaccinations. This was also a time shortly after the U.S. Food and Drug Administration began requiring certain aluminum-containing additives called adjuvants to be added to the vaccines to increase their potency. One theory is that these adjuvants cause the release of harmful chemicals called free radicals at the injection site area. Free radicals are known to damage cellular DNA and cause mutations that can lead to cancer. We know that DNA mutation is the root cause of all cancer in people and animals. Cats are uniquely in their susceptibility to tumors at injection sites. We have noticed that cats develop inflammations identical to those that precede tumors where antibiotics or even sterile water are injected. One theory about cat fibrosarcomas is that hair is carried in with the injection causing an inflammation that can lead to tumors. Another is that cats that develop sarcoma tumors have a gene that makes them more susceptible to this form of cancer. This gene remains “off” through most of the cat’s life and usually causes no problems. However, the gene can be turned “on” by inflammation or infections under the skin. So anything that causes an inflammation, could turn on that gene causing a sarcoma to form. We know that some cats are just genetically more susceptible to these tumors than others. These susceptible cats may carry strains of a virus, the Synder-Theilen, McDonough or Garden-Rasheed virus that in conjunction with tumor-causing genes (oncogenes or proto-oncogenes) lead to fibrosarcoma tumors.

From what you have read so far it should be clear that we do not understand exactly why some cats develop tumors while others do not.

Do remember that approximately 99.98 percent of cats do not develop post-vaccination tumors. However, in a very small percentage of cats, a post-vaccination inflammation develops under the skin. These reactions are abscess caused by irritation and inflammation due to vaccine components. The reactions occur 7 – 12 days after a vaccine is given, and feel like small, firm lumps under the skin. They are not painful and last a week or two. They usually subside without any lasting effect.

Description Of The Tumor:
In cats that go on to develop tumors the lump is usually over two centimeters in diameter (a bit larger than a grape) and still increasing in size thirty days after the vaccination. Feline fibrosarcomas form in the loose connective tissue located between skin and the muscle layers. This layer is called the subcutis. The skin over the tumor is elevated so it can be easily felt with your fingers. The problem with this tumor is that cancerous cells extend outward into what appears to be healthy skin , subcutis and muscle. This is why so much tissue needs to be removed to stop its spread. Because we can never be sure all of the tumorous cells were removed during surgery we often suggest that the cat undergo radiation therapy, chemotherapy or both at a major veterinary center subsequent to the operation.

What to Do If You Find A Lump on Your Cat:
First of all, remember that almost all vaccine reactions disappear over time and do not cause cancer. I have been practicing for over 35 years and have not seen a single case of fibrosarcoma in my patients. If you notice a small lump at the site of vaccination that persists more than a week call the veterinarian who administered the vaccinations and have him or her re-examine the cat. Most veterinarians are more than happy to do this. Generally, their advice will be to wait a few weeks more for the swelling to go away. If it turns out to be an abscess the veterinarian may drain it and place the cat on antibiotics.

Things You And Your Veterinarian Can Do:

1) Use only non-adjuvented vaccines in your cats. Adjuvented vaccines give us longer terms of immunity but they also cause considerably more local tissue inflammation than non-adjuvented vaccines. Vaccine manufacturers are quickly shifting to vaccines that do not contain irritating enhancing chemicals. These new vaccines will be less likely to cause tumors.fibrosarcoma cat
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2) Request that your veterinarian use 25 gauge needles when administering vaccines to your cat. Small hypodermic needles are less likely to carry irritating hair and debris under the skin.

3) Request that your veterinarian massage the area where the vaccine was administered. Massage spreads out the antigen (vaccine) lessening inflammation.

4) A somewhat gruesome suggestion that has been made by some academicians is that the vaccination be administered in a leg. The theory is that if a tumor should develop the leg could be amputated saving the cats life.

5) Avoid over vaccinating your pet. There is scientific evidence that panleukopenia and feline leukemia vaccinations last for at least three years, probably more. Yearly vaccination for these diseases is not necessary annually. Since yearly rabies vaccination is required by State law, be sure a non-adjuvented rabies vaccine is used.

6) Be sure your veterinarian keeps accurate records of the brand of vaccine used and the site where it was given. Although this may not help your pet, it will help us to determine which brands of vaccine may be causing problems. To identify the vaccine used, it is now recommend that the feline panleukopenia-calicivirus-chlamydia-rhinotracheitis vaccination be given on the right shoulder. Rabies vaccination should be given on the right rear leg as far down the leg as possible. Feline leukemia vaccination should be given on the same spot on the left rear leg

7) All cats should receive at least one feline leukemia virus test. This retroviral testing will ensure that the feline leukemia viruses not acting as a helper virus for the production of a feline sarcoma.

Newer, Safer Vaccines:

Several Pharmaceutical companies have or are in the process of marketing intranasal vaccines for cats which are applied into your cat's nose. The Heska Corporation of Ft. Collins Colo. has just launched two new intranasal vaccines designed to protect cats against feline panleukopenia, rhinotracheitis and calicivirus. (Feline UltraNasal FVRC). These vaccines are an excellent way to avoid the dangers of vaccine associated tumors.

Treatment Of Affected Cats:
Unfortunately, even with aggressive surgery alone, relatively few cats with VAS are cured. This is because cancerous cells extend outward from the distinct tumor in indistinct finger-like projections. Due to poor cure rates with surgery alone, I recommend that chemotherapy and radiation therapy be used on these cats in addition to surgery.

Treatment for VAS is still in its developmental stage. In addition to surgery, many veterinary centers now administer carboplatin or adriamycin, doxorubicin and cyclophosphamide to enhance cure rates. For the highest cure rates possible, electron beam radiation therapy is probably also beneficial. With these techniques 80% of the cats remain tumor-free for an additional two years.

Another technique employs the additional use of Carravet Acemannan immunostimulant manufactured by Carrington Laboratories injected into and around the tumor prior to surgery. This product apparently increases the likelihood that all tumor cells will be encapsulated and excised. Still another experimental technique used the administration of intradermal lipopolysaccharide from a bacterium, Pantoea agglomerans (LPSp) in conjunction with cyclophosphamide.

My conception of this problem rests on my never having encountered a single case of this disease. Veterinarians in referral practices and veterinary colleges who see it frequently are better prepared to treat it than I am. I would suggest that cat owners who are face with this unfortunate disease approach a major veterinary center as soon as the diagnosis is made to give their pet the greatest chance for survival.

Since the writing of this article many non-adjuvanted vaccines have come onto the market. We theorize that these may be less inflammatory and so less likely to cause tumors. One such vaccine, Meriel's canary pox feline leukemia vaccine is being marketed in 2005 with a transdermal injection system that eliminates the need for needles. Since the injection tract is very narrow, it may be less likely to stimulate a tumor.

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