Feline Injection-Site Sarcoma: Causes, Diagnosis, Treatment and Prognosis

What is feline injection-site sarcoma (FISS)?

Feline Injection-Site Sarcoma or FISS is a cancerous growth that can result from an injection. FISS is typically aggressive, but local tumour growth arising from the site of an injection. 

Now, before you freak out and decide to not vaccinate your cat, we request you to go through the entire article. 

Feline Injection-Site Sarcoma is NOT very commonly seen in the Indian breed of cats. Most importantly, the yearly vaccines our cats receive have near zero chances of causing FISS. 

So, why do you need to know about FISS? Because injections other than their yearly vaccines can also cause the growth of these tumours.

What causes injection-site sarcoma in cats?

Injection-site sarcomas, as the name suggests, arise where the cat has previously been injected. So, simply speaking ‘injections cause injection-site sarcomas’. Between 1 and 10 out of 10,000 cats develop FISS after a vaccine or injection. 

Do all injections cause injection-site sarcomas in cats? Absolutely not!

So, what can cause injection-site sarcomas in cats?

1. Genetic predisposition (some cats are genetically hardwired to have adverse reactions to particular injections)
2. Feline leukaemia vaccine (FeLV)
3. Rabies vaccine (containing adjuvants)
4. Injections of long-acting penicillin-derived antibiotics
5. Injections of long-acting steroids (glucocorticoids) 
6. Adverse reactions to non-absorbable sutures
7. Microchipping your cat

Now, you must already be thinking about foregoing vaccination altogether. Let us assure you of two things –

1. The CRP vaccines used in India do not contain any adjuvants and have no records of causing injection-site sarcomas. The diseases prevented by the CRP vaccine, however, have a combined 92% mortality rate. 
2. The anti-rabies vaccine can be safely administered to reduce the risk of FISS to near zero, but your veterinarian should vaccinate your cat as per the WSAVA and AAHA guidelines. It is crucial to vaccinate your cat against rabies since rabies is 100% fatal AND you can speak to your veterinary care provider about vaccines that provide protection for 3 years!

How is feline injection-site sarcoma diagnosed?

So, here’s the tricky part – feline injection-site sarcomas do not begin growing immediately after an injection. The gap between the injection and the tumour growth can be anywhere from 5 months to 5 years. 

The diagnosis typically begins with the cat parent noticing a lump while playing or cuddling with their cat. Once the cat parent notices the lump they typically take the cat to a veterinarian. 

The veterinarian may ask the pet parent to observe if the tumour is persistent for over 3 months! If the tumour remains or grows larger than 2 cm it ideally calls for a needle biopsy (fine needle aspiration cytology or FNAC). If the tumour continues to grow 1 month after the injection, your veterinarian will move forward with further diagnostic tests. 

It is quite challenging to determine the nature of a growth from physical examination only. A FNAC is NOT always the harbinger of bad news. 

However, if the biopsy results come back positive for sarcoma, the veterinarian will recommend additional diagnostic tests including a CT-Scan, USG and/or MRI to determine the edges and extent of invasiveness of the tumour. 

The doctor will also recommend additional blood tests, biochemistry tests and X-rays to make sure the cat is healthy enough for surgery and/or radiation and chemotherapy. 

Thankfully, although aggressive, these cancerous tumours grow locally. Cases of metastasis or the involvement of other organs are rare especially if diagnosis and treatment is begun early. 

What is the treatment of feline injection-site sarcoma?

There are quite a few approaches available for the treatment of injection-site sarcoma in cats. The ideal choice of treatment depends upon the location of the tumour, staging of the tumour, overall health of the cat, and the medical infrastructure available. 

Surgery for Feline Injection-Site Sarcoma

CT-scan, X-ray and biopsy typically precede a tumour removal surgery. Feline injection-site sarcomas (early stages, without metastasis) typically have clean edges so it is easier to operate and remove the tumour in its early stages. 

Chemotherapy for Feline Injection-Site Sarcoma

Chemotherapy for cats is usually recommended along with surgery for feline injection-site sarcomas to prevent relapses. 

Chemotherapy is also recommended by veterinarians if they observe or suspect any metastasis of the sarcoma. 

Radiation Therapy for Injection-Site Sarcoma in Cats

Radiation can be given locally before or after surgery. Radiation for FISS in cats is uncommon in India. However, several new-age clinics provide veterinary radiation therapy for cats with injection-site sarcomas outside India. 

Immunotherapy for Injection-Site Sarcoma

It is an aggressive but less invasive therapy to treat injection-site sarcomas in cats. Immunotherapy for feline injection-site sarcoma with the IL-2 vaccine is still considered an alternative therapy method. It is rarely available in India.

Combination Therapy for FISS

A combination approach for the treatment of feline injection-site sarcoma usually reduces the risk of tumour relapse in cats. It works better than surgery or chemotherapy alone. 

A combination therapy might include surgery, chemotherapy and/or radiation to treat FISS aggressively. 

Is injection-site sarcoma in cats curable? How long do cats with feline injection-site sarcoma survive?

Sadly, despite the best efforts from some of the most well known veterinary institutes across the world, feline injection-site sarcoma has a high recurrence rate. 

Nearly 50% of all cats who are diagnosed and treated for FISS show relapse in the next 2-5 years! It is seen in cats even if their tumours were resected cleanly. Around 86% of all cats who relapse show tumour growth within 6 months of tumour removal surgery. 

How to prevent feline injection-site sarcoma in cats?

The only way to prevent feline injection-site sarcomas is by knowing and remembering which injections can trigger the growth of the cancer and speaking to your veterinarian about your concerns clearly! 

Although costly, try to opt for the vaccine that offers 3-year protection against rabies instead of vaccinating your cat once every year. 

During neutering or spaying, ensure that you choose a veterinarian who knows about cat health and wellness. 

Avoid administering vaccines and injections by yourself. Get explicit permission from your veterinarian if you need to administer antibiotic injections to your cat. 

Your veterinarian should follow the AAHA guidelines for vaccination of cats. 

The AAHA Guidelines for the vaccination of cats

The AAHA Guidelines suggest vaccinating cats only on their limbs and/or tails. 

The main reason behind this suggestion is, if there is an aggressive tumour growth in any of the limbs or tail, the limb can be amputated to save the cat’s life. Removal of the entire limb or tail ensures almost zero chances of feline injection-site sarcoma relapse. 

Why should you get your cat vaccinated from experienced veterinarians only?

Experienced veterinarians are aware of the compositions of all the cat vaccines available in India and the risks they bear. 

At the same time, they know how and where to vaccinate your cat to minimise the risk of feline injection-site sarcoma development. 

An experienced veterinarian will also recommend a rabies antigen titre check before vaccinating your cat against rabies to minimise the risk of the development of feline injection-site sarcoma.