What causes fibrosarcoma in cats Diagnosis and Treatment

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cat laying down
Cat Laying Down

Cancer is not a word anyone likes to hear, say or even think of but unfortunately our pet cats are not immune to it. A fibrosarcoma is a type of cancer that occurs in cats and it's something that all cat owners should be aware of.

What Is a Fibrosarcoma in a Cat?

A fibrosarcoma is a type of cancerous tumor that occasionally occurs in cats. It is a mass that usually occurs in the skin of a cat at the site of an injection or vaccination. Because of this, fibrosarcomas are also referred to as injection site sarcomas or vaccine associated fibrosarcomas.

Symptoms of a Fibrosarcoma in a Cat

There are only a few indications that a cat has a fibrosarcoma.

Signs of Fibrosarcomas in Cats

  • Lump under the skin at the site of a vaccination
  • Lethargy
  • Decreased appetite

Cats with fibrosarcomas will develop a palpable lump or mass under their skin after an injection or vaccination has been administered. This lump can appear within a couple of days, months or even years after the injection and be locally aggressive but fibrosarcomas are slow to spread to other parts of the body. Since most vaccines are given over the shoulders or hips of a cat, fibrosarcomas are commonly seen in these areas.

fawn pug lying on red textile
fawn pug lying on red textile

In addition to the lump, if a cat has a fibrosarcoma that has not received treatment it may start feeling sick. Lethargy and a decrease in appetite may be seen in this case but typically there are no signs of a fibrosarcoma other than seeing the lump itself.

Causes of Fibrosarcomas in Cats

Inflammation is the common denominator among causes of fibrosarcomas, regardless of how the inflammation begins.

  • Vaccinations: There is a growing concern for fibrosarcomas that occur after a vaccination has been administered. These tumors may not appear for years but are always where the vaccine was given. It is thought that the local inflammation caused by the vaccine or the adjuvant in the vaccine can contribute to the formation of fibrosarcomas but it is still not fully understood.
  • Injections: It isn't just vaccinations that can cause fibrosarcomas to form. Injections of steroids, vitamins, pain medications, saline and other things may also cause a fibrosarcoma to form due to the local inflammation that happens when a substance is injected under the skin. It is thought that some cats simply have different genetics that make them more likely to develop this issue.
  • Foreign bodies: Items that may end up under the skin of a cat such as a microchip or a shard of plastic in a wound can cause inflammation that results in a fibrosarcoma. It has even been considered by researchers that microscopic aluminum compounds are considered to be foreign material from vaccines. In some cases, these compounds are still present under the skin and cause inflammation that leads to a fibrosarcoma.
  • Feline sarcoma virus: Feline sarcoma virus (FeSV) is a rare hybrid virus that causes an extremely fast growing type of fibrosarcoma. According to research, this virus only occurs in 2 percent of cats and they are typically young ones that have also contracted Feline Leukemia Virus (FeLV). These rare types of fibrosarcomas typically grow very fast.

Diagnosing a Fibrosarcoma in a Cat

If a mass is felt in the area of a previous injection a fibrosarcoma will be seriously considered by a veterinarian. In order to diagnose a cat with a fibrosarcoma, a biopsy or fine needle aspirate will be obtained in order to look at the cells inside the mass. This will tell the veterinarian why type of mass it is.

selective focus photography of tan and black puppy on brown surface
selective focus photography of tan and black puppy on brown surface

Treatment of Fibrosarcomas in Cats

Radiation, chemotherapy and surgery are needed to treat a fibrosarcoma in a cat. These tumors are locally aggressive which means they can be difficult to completely remove. They do not typically spread to other parts of the body but they can be problematic where they appear. Sometimes amputation of a limb is needed to completely remove a fibrosarcoma.

How to Prevent Fibrosarcomas in Cats

Since it appears that many different types of foreign items introduced into a cat's body can cause inflammation and therefore also a fibrosarcoma, the concern for over-vaccinating a cat has been discussed by professionals. Following your veterinarian's recommendations for your specific cat's lifestyle will help avoid unnecessary vaccinations and therefore limit the potential to cause inflammation and fibrosarcomas.

Adjuvanted vaccines are also a concern for causing fibrosarcomas so you can ask your veterinarian if the vaccines they are using for cats are non-adjuvanted or live vaccines. Vaccines should not be avoided though, as there is still serious risk for the diseases that these injections help prevent.

Some types of low dose vaccinations exist for cats which may limit how much foreign material is being introduced to a cat. There is no data saying whether or not this is a way to prevent fibrosarcomas but it may help decrease the amount of inflammation in the body and therefore limit the likelihood of a fibrosarcoma developing.

brown dog in front of fence
brown dog in front of fence
tan dog
tan dog
white and brown short coated dog
white and brown short coated dog

When possible administer your cat oral medications and supplements instead of injections. Sometimes injections cannot be avoided but other times there are oral options that may avoid the inflammation that many injectable medications can cause.

Some people elect to avoid microchips in order to limit their cats' chances of developing inflammation and a fibrosarcoma. A popular alternative to a microchip is collar or harness identification including GPS tracking, even though this option can fall off of a cat unlike a microchip.

Finally, it may not be a form of prevention but many veterinarians are now administering vaccinations on the legs and tail instead of around the neck and hips. This allows an option for complete removal of a tumor and appendage if a fibrosarcoma does occur as opposed to another location, such as the neck. This will make treatment easier if it becomes necessary.