Fibrosarcomas in Cats

Key Takeaways

Fibrosarcomas are a group of malignant tumors (cancer) that originate in fibrous connective tissue.

• This type of tumor develops slowly and does not often spread, but can cause extensive tissue damage

• In cats, fibrosarcomas can be found in most areas of the body, including on or under the skin and in the mouth

• Symptoms vary depending on location but include a palpable mass under the skin, weight loss, lethargy, oral bleeding, and difficulty walking

• Diagnosis is made using microscopic examination of cells collected from the mass, diagnostic imaging, bloodwork, and biopsy

• Treatment depends on the location, shape, and spread of the tumor but includes surgery, chemotherapy, radiation, and palliative care

• Prognosis varies widely depending on the type and location of the tumor

A Closer Look: What are Fibrosarcomas in Cats?

Cancer is a general term referring to abnormal, uncontrolled cell growth. Cancerous cell growth usually leads to an accumulated mass of cells called a tumor. Fibrosarcoma is a specific type of tumor that arises in fibrous connective tissue. Fibrosarcomas may be found anywhere in the body, but common locations in cats include the mouth and under the skin.

Any new lumps found in cats warrant prompt veterinary attention. Left untreated, fibrosarcomas can become life threatening.

Risk Factors

The incidence of different types of fibrosarcomas varies widely. Oral fibrosarcomas are common, while the virus-induced form is rare. Cats with permanently-placed medical devices may have slightly increased risk for developing a fibrosarcoma. Previous radiation therapy may also lead to an increased risk. 

Symptoms vary depending on the localization, size, and spread of the tumor. Some symptoms can include;

Weight loss


Hair loss around the mass

• Oral bleeding

Some fibrosarcomas break open and bleed. This may lead to secondary infections with redness, swelling, and discharge. 

Specific localizations of fibrosarcomas may have breed, age, or environmental risk factors. There are rare types of fibrosarcomas that have high risk stimuli; injection-site sarcoma, viral fibrosarcoma (caused by feline leukemia virus infection), and trauma-related fibrosarcoma caused by injuries around the eye.

Possible Causes

Most fibrosarcomas arise spontaneously with no identifiable cause. Fibrosarcomas are slow growing tumors arising from fibrous connective tissue. Depending on the location of the tumor, genetic and environmental factors may contribute to the development of fibrosarcoma.  

Main Symptoms

The symptoms vary immensely depending on the localization of the fibrosarcoma. Generally, they involve a swelling or mass which may be felt or seen if it is near the surface of the skin.

Testing and Diagnosis

After a physical examination and medical history, a pet with symptoms of a fibrosarcoma typically undergoes a number of diagnostic tests, including: 

• Fine needle aspiration and cytology

• Diagnostic imaging (X-rays, ultrasounds, CT scans)

• Bloodwork

• Urinalysis

• Biopsy

Steps to Recovery

Treatment varies depending on the location but can include;

• Surgical removal

• Chemotherapy

• Radiation

• Palliative care

• Symptom management

• Pain management

Prognosis varies depending on the location of the tumor and how straightforward attempts at surgical removal prove to be. Subcutaneous fibrosarcomas that are able to be fully excised and treated with radiation have a fair prognosis while one which is on a major organ or has metastasized is more likely to have a poor prognosis.


Most fibrosarcomas arise spontaneously so there is no way to prevent them. Overall monitoring of pet health and changes in behavior may allow for the condition to be caught earlier in development to begin treatment as rapidly as possible. Fibrosarcoma is not contagious.

Are Fibrosarcomas Common in Cats?

Fibrosarcomas are a common type of malignant tumor in cats. Oral fibrosarcomas in particular are the second-most common type of oral tumor in cats.

Typical Treatment

• Surgery

• Chemotherapy

• Radiation

• Palliative care

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