The Perfect Guide to Fibrosarcomas in cats

If you’re a cat mom or dad, you know that one of the main concerns you have is your feline friend’s safety. And one of the most common health concerns for cats is fibrosarcomas. In this article, we’ll introduce you to fibrosarcomas and discuss the risks and benefits of getting them checked out. We’ll also give you a guide on how to tell if your cat has one, and some tips on how to care for them if they do. So read on to learn everything you need to know about fibrosarcomas in cats!

Fibrosarcomas in cats are fairly commonly observed veterinary medicine and occur in humans as well.  As with many kinds of cancer, the reasons a fibrosarcoma develops, and the location where it develops, may be at best speculative.  We really do not have all the answers yet.  On occasion in veterinary medicine we observe vaccine induced cancer called fibrosarcoma.

Fibrosarcomas in cats

A FIBROSARCOMA is a malignant (invasive) cancer originating from fibrous connective tissue.  Fibrosarcomas may spread (metastasize) to other areas of the body.Post surgical specimen of a feline fibrosarcoma tumor.A FIBROMA is a benign (non-invasive) neoplasm (tumor) composed primarily of fibrous tissue.  These do not spread to other areas of the body.

In recent years the topic of vaccine induced fibrosarcomas in cats has been a serious concern of cat caretakers, veterinarians, and the pharmaceutical companies that make vaccines for cats.  Unquestionably, vaccinations have prevented uncountable deaths in dogs and cats through the years.  Just as in human medicine where such diseases as smallpox and polio are no longer health threats due to wide distribution and use of vaccines, so too in veterinary medicine have serious diseases been kept in check by intelligent use of animal vaccines.  

However, there can be a downside to the wonderful miracle of vaccines.  On occasion, and that occasion may be only a single adverse reaction in 50,000, there may be an undesirable outcome for the patient receiving the vaccination.  Read Dr. Dunn’s article on the use of vaccines in dogs and cats.

One unique type of adverse reaction is seen in cats after having been vaccinated for certain feline diseases.  Adjuvants are often added to killed (inactivated) vaccines to enhance the immune response; a common adjuvant is aluminum salts and these aluminum deposits are often seen in the microscopic analysis (histopathology) of a section of the offending tumor.  There is speculation that adjuvants may be the inciting agents that stimulate a reaction at the vaccine site and which eventually leads to cancer formation.  All the facts are not known at this time and many researchers are currently working to find the answers to the vaccine induced sarcoma problem in cats.
Progress is being made, though, and scientists and veterinarians are beginning to understand the complex variables that factor into tumor formation at vaccine sites.  Some of those factors are location of vaccine administration, type of vaccine and adjuvant, frequency of vaccine deposition in a localized area of the cat, and the state of health of the cat at the time of the vaccination.  Hopefully, in the near future these variables will be understood and adverse vaccine reactions will no longer be a consideration when we attempt to protect our feline friends from some very real and dangerous diseases. 

Fibrosarcoma Removal In A Cat

This patient, a 16 year old domestic long-haired cat, was presented with a rapidly growing mass over the back near the shoulder blades.  The physical exam was otherwise normal and the blood chemistry and blood cell analysis of the patient was normal.  Surgery was elected as a method of prolonging the patient’s life.  The patient was anesthetized with Isoflurane inhalant anesthetic and recovered quickly and with no complications.
The site over the shoulder 
blades is prepared for surgery
The surgeon begins the incisionThe mass is carefully isolated.
  This mass had a large 
cyst within it
Any observable abnormal tissue 
is removed… difficult when 
there is tumor invasion of 
surrounding healthy tissue.
The tumor bed is carefully 
inspected for abnormal tissue
A view of the excised tumor
A view of the depth of the tumorVaccinations are a very important 
health care tool.  Consult with your veterinarian for recommended protocols.
The surgical area immediately 
post operatively. Sutures are 
removed 10 to 12 days later

The histopathology report on two areas of the excised tumor follows:


 Haired skin, subcutis and skeletal muscle from back: FIBROSARCOMA


Within the subcutis and skeletal muscle there is a malignant neoplasm composed of mitotically active spindle cells that have produced collagen.  Completeness of excision cannot be judged.  Neoplasms of this type are locally invasive and prone to local recurrence; eventual metastasis occurs in some cases.

In this patient, frequent monitoring of the surgical site will be needed in order to reveal any new tumor growths at an early stage.  Removal of small nodules of tumor are much less invasive for the patient and usually will provide for more thorough removal than tumors that have had the chance to grow over long periods of time.

Update:  This patient was euthanized one year after this surgery.  The tumor regrew and the pet owner elected not to have any additional surgery performed.  The owner was happy that an additional year of reasonably happy life was enabled by the first surgical procedure.

In the end, no doubt, fibrosarcomas are one of the most devastating tumors in cats. They can cause severe health issues as well as long-term effects on your pet’s mobility and quality of life. That is why it is important to diagnose early and take necessary steps to ensure these cancers do not spread until they are contained.

In case you missed it, you may also read our blog article titled “What are the symptoms of fibrosarcomas in cats?” Here you will find all about what these cancerous tumors look like so that you don’t miss a single symptom. Furthermore, we also recommend keeping an eye out for any changes in your cat’s physical or mental health when dealing with this type of tumor – especially before its detection becomes too late!

Frequently Asked Questions

How aggressive is fibrosarcomas in cats?

While metastasis (spread to other organs) has been reported as being uncommon, these tumours frequently behave aggressively by infiltrating the local and surrounding tissues. When examined under a microscope, certain fibrosarcomas appear non-aggressive (low grade), although nevertheless act violently.

How long does it take for fibrosarcoma to develop in cats?

Cats with tumours will eventually die from tumor-related problems if they are not treated. The average interval between immunisation and the onset of a tumour is 3 months to 4 years. A smaller proportion of cancers appear five or more years following the vaccination.

What are fibrosarcomas associated with in cats?

Tumors called “vaccine related fibrosarcomas” develop where cats have received vaccinations. Most frequently, they are connected to the rabies vaccine and the vaccine against the feline leukaemia virus.

Leave a Comment