Feline Injection Site Associated Sarcoma (FISS)

In rare cases, conjunctival tumors can develop at puncture sites in cats, which must be surgically removed. We explain the risk of injections.

A little swelling after vaccination or injection is normal. However, if the swelling does not go away at all and tends to get bigger, you should have it checked out by a veterinarian. In the worst case, it could be a feline injection site-associated sarcoma (FISS).

How Does FISS Develop in Cats?

FISS is a tumor of the connective tissue that can develop, among other things, in a skin area in which the cat received an injection a few months or years previously. FISS develops relatively rarely, estimated to occur in only 1 to 4 out of 10,000 vaccinated cats.

Affected cats usually become ill at the age of eight to twelve years, but can also be younger in individual cases. So far, little is known about the causes of FISS. It is assumed that chronic inflammation damages the connective tissue cells in such a way that they degenerate into tumor cells.

Inflammation can be triggered by:

  • injuries
  • Foreign body
  • insect bites
  • Side effects of vaccinations or drug injections

However, since less than one percent (0.01 to 0.04 percent) of cats develop FISS after injection, there is a high probability that affected animals also have an inherited predisposition to develop tumors.

Risk Factors for the Development of FISS

Which factors favor the development of FISS? There are many studies about this. The following factors have been documented so far:

  • A number of injections at one site: more injections, higher risk.
  • Injection site location: If the injection is between the shoulder blades, the risk of FISS is greater.
  • Temperature: If the injection solution is cooler than the ambient temperature, this affects the risk of inflammation at the injection site.
  • Use of adjuvants (e.g. aluminum salts): These are boosters in vaccines used to improve the immune response.
  • Heredity: One study showed a higher risk in siblings of cats with FISS.

That’s How Long You Should Monitor Puncture Sites

The American Veterinary Medical Association AVMA recommends checking vaccination or injection sites for a few weeks after treatment in order to detect any changes at these sites at an early stage. If the swelling at the vaccination site, which is completely harmless in most cases, tends to get bigger or does not go away during this time, it should be examined by a veterinarian.

Older cats, who generally have an increased risk of cancer, should be checked regularly for swellings in or under the skin. If you discover a small swelling or nodule, you should note the date of the day of finding, the affected body part, and the size of the small lump. The entries help enormously to quickly recognize whether the swelling is gradually getting bigger or is showing other changes.

A veterinarian should be consulted immediately for tumors with a diameter of more than one centimeter.

Prevent Development of FISS

Unfortunately, there is no 100% protection against the development of a FISS. But there are expert recommendations on how to reduce the risk of developing FISS:

  • Vaccination – as much as necessary, as little as possible.
  • Only vaccinate or inject in parts of the body where a tumor can be easily removed.

The health risks for the cat from incomplete immunization protection or the failure to receive important treatment are much greater than the risk of developing FISS.

Cat Has FISS – How to Treat?

If FISS is suspected, the veterinarian will take tissue samples and have them examined under a microscope by a specialist laboratory to rule out other causes of the growth. If there are degenerated connective tissue cells in the tissue sample, this strengthens the suspicion of FISS. However, the veterinarian can only make a definitive diagnosis once the tumor has been removed and examined as a whole.

The more the FISS has grown into the surrounding tissue, the worse the chances of a final cure. However, depending on the severity of the tumor, cats can still have a good life for a while with appropriate treatment and care. However, as soon as the animal suffers and no longer responds to the therapies, you should allow it a gentle, painless death.

Mary Allen

Written by Mary Allen

Hello, I'm Mary! I've cared for many pet species including dogs, cats, guinea pigs, fish, and bearded dragons. I also have ten pets of my own currently. I've written many topics in this space including how-tos, informational articles, care guides, breed guides, and more.

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