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We all know that older cats, like older people, are more susceptible to cancer. But beginning in the late 1980’s, veterinarians began to see a strange tumor occurring on the body of cats at much too young an age. Pathologists, examining these tumors, found that most were composed a malignant, mutated form of the fibroblast cell, a cell type that basically holds all the organs and structures of the body together (connective tissue). These particular fibroblasts (subcutaneous) were the ones that help bond the skin to the muscle and bone structures below. The tumors were named feline vaccination-related fibrosarcomas or VAS for short. Before these tumors appeared, veterinarians had access to vaccines that were injected deep into the pet's muscles (intramuscular) - like the tetanus shots you receive. But the newer cat and dog vaccines of the time were designed to be given just under the skin (subcutaneously) or intramuscularly. Vets liked the subcutaneous vaccines. They seem to cause less discomfort to pets and because of the immune system cells that naturally dwell there, some thought that giving them under the skin produced higher levels of immunity. Given subcutaneously, they were also much less likely to hit a major nerve.
Both male and female cats and all breeds appear equally susceptible to VAS. The rate of growth of these tumors is highly variable. Some begin to develop as early as a few weeks after a vaccination, others not for many years. They spread slowly and your veterinarian can usually remove them - but they have a nasty tendency of coming back. Usually, they returned in the same general area where they had been removed, but in a few cases they had moved to other locations in the cat's body.
The original outbreaks were along the North Atlantic coast of the United States - particularly Pennsylvania. An exceedingly astute veterinary pathologist at PennVet, Mattie Hendrick (whose photo I placed above), associated the increasing number of these tumors that came her way with a similar pathology she had seen in post-vaccination site inflammations. She also made a mental note that the increase in the number of these tumors coincided with the first enactment in Pennsylvania of a mandatory yearly rabies vaccination requirement for cats (ref1, ref2)
The chance of your cat developing one of these tumors is quite small. We think that perhaps 10-20 cats per 10,000 might developed them. Several years before the tumor’s appearance on the East Coast, there had been an outbreak of rabies in raccoons in the area which is what motivated the change in Pennsylvania law. 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. Veterinarians became suspicious that the adjuvants might be a part of the problem.
However, something else must have happened in North America that we still do not understand. That is because we still see VAS occurring more frequently in cluster areas. We veterinarians all use the same vaccines and supplies - so how can this be? Perhaps veterinarians in different areas give vaccinations differently because they were taught to do so differently in their regional veterinary schools. Perhaps the genetics of cats differ from area to area or some other factor in the higher-incidence areas is somehow partially responsible. No one knows for sure. And because we veterinarians understand so little about the drivers of fibrosarcoma in cats, their recommendations and mine on how one might prevent them are no more than guesswork. (ref)
Ninety-Nine percent of cats do not develop post-vaccination tumors ;
But for those that do that is little consolation :
Cats seem to be unique in their high susceptibility to inflammation and tumors at injection sites. That must have something to do with the way cats respond to skin and subcutaneous trauma and irritants. Veterinary pathologists have noticed that some cats develop inflammations identical to those that precede tumors when antibiotics or even sterile water are injected under their skin. Their violent response to contaminated puncture wounds is quite dramatic too. One theory about cat fibrosarcomas is that occasionally a 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. As the theory goes, this gene remains “off” throughout 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 inflammation in the injection site area could turn on that gene causing a sarcoma to form. In humans and laboratory animals, chronic inflammation is know to be a prelude to cancer formation. (ref1, ref2, ref3) Some describe the environment around chemical irritants such as vaccine ingredients as "a stromal “soil” that is enriched with cytokines and growth factors" that can promote cancer. (ref1, ref2). Cats just seem to be more susceptible to that problem than other species. Again, no one really knows why. Cats have many idiosyncrasies: their inability to utilize carbohydrates efficiently, their need for high dietary fat levels, their lack of specific liver enzyme systems, their need for pre-formed vitamin A.
What Do These Tumors Look Like ?
Please remember that the vast majority of lumps, bumps and swelling that occasionally occur shortly after vaccinations will go away with time and do not lead to fibrosarcomas. If such a situation is accompanied by changes in the cat's behavior, get on the phone with the veterinary staff that administered the vaccine as soon as possible and ask for advice. When not accompanied by behavioral changes, these lumps, bumps and swellings should be completely gone in a week or two. Whether you should consider them a warning to modify your decisions on future vaccinations for your cat is something you will have to decide for yourself. You know how I feel about over-vaccination.
When a cat is developing a vaccination-related fibrosarcoma, owners might notice a small lump when they are petting or grooming their pet. These lumps are usually about a centimeters or two in diameter and a bit flattened and oblong by the time they are noticed under the pet's skin.
Normally, your veterinarian can easily surgically remove tumors of this size. They do that in their canine patients all the time. The problem with this particular type of tumor in cats is that its cancerous cells often extend invisibly outward like fingers into what appears to be healthy skin tissue, and muscle.
What to Do If You Find A Suspicious Lump on Your Cat :
As I said, most vaccine reactions are not cancerous and disappear within a few weeks of vaccination. If you notice a small lump at the site of vaccination that persists more than a week or two call the veterinarian who administered the vaccinations. Have him or her re-examine the cat. If you are a worrier, don't wait that long. Most veterinarians are more than happy to have another look at your cat without charge. It should be the veterinarian who reexamines your cat - not one of their technicians.
Generally, their advice will be to wait a little longer for the swelling to go away. We wait because a small percentage of cats, do develop transient a post-vaccination inflammation. These reactions are usually sterile abscesses caused by irritation and inflammation due to some of the vaccine components. These reactions occur 7 – 12 days after a vaccine is given, and also feel like small, firm lumps under the skin. They seem to go away without any lasting effect. You can request that the veterinarian call the company that manufactured the vaccine for advice on what would be the safest thing to do. Don't bother calling some government agency because they will just blow you off.
Things You And Your Veterinarian Can Do To Prevent Fibrosarcomas :
1) Give no more vaccinations than your cat requires. We tend to vaccinate cats far too often. Adult cats do not require yearly vaccinations. When you do take your cat in for rabies vaccination, request a recombinant rather than an inactivated vaccine and one that has been tested and approved for three years duration of immunity. These more advanced formulations might to be less likely to cause injection-site sarcomas. (ref) Giving your cat vaccines is not the same as paying your yearly tax assessments. Beware the postman’s delivery of yearly pet vaccination "reminders”, emails or the appearance of the “vaccination bus” at your local supermarket or pet megastore. Their motivation is not what it appears.
2) Give booster vaccinations only when your cat's immunity has been documented to be low. The cat's level of circulating antibody and possible need for a booster vaccination can be determined by running blood titers. Even low-titer cats can be resistant to infection because of the innate immunity they posses and immunological memory - two things not measurable through blood titer tests.
2) Use only three-year, non-adjuvanted vaccines in your cat. Adjuvanted vaccines might give us longer terms of immunity or higher titers, but they also cause considerably more local tissue inflammation than non-adjuvanted vaccines. Vaccine manufacturers are quickly shifting to vaccines that do not contain irritating enhancing chemicals. We are hopeful that these new vaccines might be less likely to cause fibrosarcoma tumors. Whenever possible, use vaccine boosters that are administered intra-nasally.
3) Request that your veterinarian use 25 gauge needles when administering vaccines to your cat. Perhaps smaller hypodermic needles are less likely to carry irritating hair and debris under the skin.
4) Request that your veterinarian massage the area where the vaccine was administered. A thorough massage outward from the injection site might spreads out the antigen (vaccine) lessening inflammation. I have always done this. To my knowledge, no cat of any client of mine ever developed a fibrosarcoma. Recent studies do not confirm that massage decreases the development of Fibrosarcomas. (ref1, ref2) Perhaps I do it more thoroughly, perhaps massage played no part in my lack of experiencing these tumors. But I will continue to do it all the same.
5) Some veterinarians that see cases of VAS have begun giving their vaccinations in the lower rear leg. Although this technique might appear to be somewhat more painful, they realize that a tumor occurring on the lower leg would allow the leg to be lost but the cat to be saved.
6) Be sure your veterinarian keeps accurate records of the brands of vaccine used and the sites where they were given. Although this may not help your pet, it will help us to determine which brands of vaccine may be more likely to cause 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 on the right rear leg as far down the leg as possible. Feline leukemia vaccination given on the same spot on the left rear leg.
7) Many medications (such as corticosteroids, antibiotics, etc.) can be given in pill form rather than by injection. The medication in most tablets will be in your cat's blood stream in less than an hour. So unless there is a pressing need for immediate action, avoid as many injections as you can for your cat. I know that cats are hard to pill - but the same study I referred to above (rptref) appeared to find a relationship between non-vaccine injections and the formation of fibrosarcomas.
What Can Be Done If My Cat Develops A Fibrosarcoma ?
Unfortunately, even with aggressive surgery alone, not enough cats with VAS are cured. This is because as I mentioned before, the tumor is like an octopus - it often has unseen tentacles that reach out far from the visible tumor.
This means that the first attempt to remove this tumor has to be radical, major surgery. Your chances of curing your pet are greatest if this is done by a veterinary surgeon who specializes in removal of feline fibrosarcomas. Combining this aggressive surgery with radiation therapy increases your cat's chance for survival. So far, chemotherapy has not been as effective as radiation.
If you can afford it, have your veterinarian make contact with a major veterinary center where a specialist is located . This should be done as soon as the diagnosis is confirmed through biopsy to give your pet the greatest chance for survival. If you cannot afford that approach, find a local veterinarian who is up-to-date on this type of surgery because if the tumor is removed similarly to how other superficial tumors are removed, it is highly likely to reoccur quickly.
How veterinarians immunize cats, how vaccines are manufactured and how and how often we give them are all changing rapidly because of these fibrosarcomas and other vaccine-associated pathology. It appears that we are making progress because the disease seems to be shifting to older pets - pets that probably received the causal vaccination many years ago. But because we can evaluate these changes only in hindsight, it will be some time before we know which changes have been helping cats.