Pet Cancer Part II: Fibrosarcoma

Pet cancer is scary, but you aren’t in it alone. For cats, the most common cancers are feline lymphoma and feline injection-site sarcomas (ISSs). Vito had fibrosarcoma, which is vaccine-induced, so that’s what I’ll discuss here. And before you pull out your pitch fork, please read this entry in its entirety and DO NOT stop vaccinating your cats. The chance of fatal disease is much higher than cancer, and there are still many questions that need to be answered. There is clearly a link between injection sites and tumors in cats, but the reasons why are all hypotheses.

If you missed Part I and want to start at the beginning, check out Diagnosis & Decisions.

What Is Fibrosarcoma?

A type of soft tissue sarcoma, consisting of fibroblasts, which are the connective tissue that produces collagen found in scar tissue. While it’s aggressive where it appears (Vito’s tumor was large and deep), it’s slow to spread through the body.

What Causes Fibrosarcoma?

These are hypotheses. Based on Vito’s tumor’s location at the back of the neck, his cancer was likely caused by 1) his immune system’s reaction to the vaccine itself or 2) his immune system’s overreaction to the adjuvant in a vaccine (which is usually aluminum). Researchers suspect that it could be something in the certain cats’ genetics that cause the spiked immune response, but they really aren’t sure. They also don’t see it in dogs at all.

What’s an Adjuvant?

Adjuvants keep the virus in one small area while the body develops antibodies. Keeping the virus in one place causes an enhanced immune response, but an overreaction of the immune system can start the growth of the sarcoma. Why does this happen? Researchers aren’t sure, but one explanation could be that some cats genetics make them predisposed to this response.

Vaccine Administration Practices: Then & Now

Vito’s fibrosarcoma was probably from early in his life, when vaccines were given in the back of the neck. A cat would receive two at one time, in the same place.

Why did vets used to give all vaccines on the back of the neck? Because the excess skin between the shoulder blades (aka scruff) allows for the body to slowly break down the vaccine as it develops an immune response.

Now, vets and vet techs inject vaccines in different areas (ex. rabies in front leg, FVRCP in back leg), to prevent multiple vaccines from entering the same area, and to decrease the chances of a cat’s immune system overreacting.

Should I Skip Vaccines? NO!

DO NOT skip vaccines, especially for young cats. Vaccines build up their immune system, and help them live to be old! Purina states that vaccinated cats can better fight other viruses that the vaccine doesn’t even protect against. Also, the risk of getting a vaccine-induced sarcoma is lower than your cat getting a fatal disease from not being vaccinated.

Recent vaccination practices make it less likely for your cat to get a vaccine-induced sarcoma. And if she gets it, it’s easier to remove a limb (which doesn’t diminish quality of life at all) than it is to remove in the neck where Vito had it.

What Do Routine Vaccines Protect Against?

Obviously, the rabies vaccine protects agains rabies. FVRCP is the other vaccine your cat receives during annual exams. It protects against three viruses:

Feline Viral Rhinotracheitis (FVR) is triggered by the feline herpes virus (a kitty cold). According to Merck Animal Health, i’s responsible for 80-90% of feline upper respiratory infections (URIs). A kitty cold can be fetal if a cat isn’t healthy, because it causes dehydration and decreased appetite. Plus, it can turn into pneumonia, which is extremely dangerous for kittens and seniors.

Feline Calicivirus (FC) is similar to FVR (#1), but cats also get painful ulcers in their mouths. Could also lead to pneumonia in serious cases, and again is dangerous for kittens and seniors.

 Feline Panleukopenia Virus (FPV) has many names: panleuk, feline distemper, or feline parvo. Caused by the feline parvovirus, panleuk decimates the bone marrow and intestines. All cats are exposed to panleuk during their lifetimes, according to the American Veterinary Medical Association, but usually young kittens around 3-5 months of age, sick, or unvaccinated cats develop symptoms. Without super early intervention, panleuk has a mortality rate of 90%, and with kittens 8 months or younger, it’s almost always fatal. I fostered a kitten (RIP Feta) that contracted the virus panleukopenia and died. I would give anything to go back in time and make sure she lived until 13 with zero health problems like Vito.

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The Only Exception

Last point, which is a takeaway whether I decided to treat Vito or not, once a cat has a vaccine-induced sarcoma, no more vaccines. For older cats, this is really no big deal. They have very strong immune systems and are protected from years and years of vaccinations. Since fibrosarcomas can grow back, and the cat’s genetic makeup around the immune system is suspect, there is no reason to roll the dice. Your oncologist will likely tell you this during your first consultation.

Is Fibrosarcoma Treatable?

When I met veterinary oncologist Dr. Christine Mullin, I was instantly at ease. She had a kind, loving smile, and I could instantly feel her love for animals. Talking sweetly to Vito, she pet him and talked about his fibrosarcoma, and answered every question I had.

The best thing was when I heard her say, “It’s totally treatable. I would do it for my own cat.”

Relief swept over me. This wasn’t the end. In my next entry, we’ll review Dr. Mullin’s plan for treatment.

Missed Pet Cancer Part I? Read it now.

To learn more about common canine and feline cancers, visit this site and click the dropdown labeled Common Cancer Types.