Fibrosarcoma in Cats

When describing feline fibrosarcoma, vets explain that this type of cancer begins in individual cells within connective tissue, as well as just under the surface of the cat’s skin.

Fibrosarcoma is a form of soft-tissue cancer that is not uncommon common in cats. Fibrosarcoma generally grows aggressively in the cells where it first appears, but is slow to spread to other body organs or systems. Fibrosarcomas begin in the fibroblasts of the skin (cells in connective tissues) and in subcutaneous (under the skin surface) connective tissues. While some grow slowly, others may grow more quickly. After being surgically removed, fibrosarcomas can grow back. 

The cat’s owner is most likely to notice lumps just underneath the surface of the cat’s skin. These lumps can appear anywhere on the cat’s body: the head, legs, in the mouth and anywhere else on its body. The area in between the shoulder blades is most often implicated, making up for about 40 to 50% of these tutors. Other symptoms include:

• Lumps may be fleshy or firm
• The cat may not feel pain from the lumps
• Lumps are irregularly shaped

Fibrosarcomas can also develop inside the cat’s body; usually on its spine, in the pelvis, or in its ribs. Advanced fibrosarcoma causes the cat to:

• Have difficulty eating
• Lose its appetite
• Become dehydrated
• Painful walking
• Become lethargic
• Develop mysterious bleeding in its mouth

Cats can develop fibrosarcoma for one of three reasons. If the cat is older, it may be more prone to developing this particular form of cancer. 

Some vaccines have been linked to the development of fibrosarcoma, but these occurrences are relatively rare. When fibrosarcoma develops as the result of vaccinations, it is called “vaccinosarcoma” or vaccine-induced sarcoma. While vets still recommend that cat owners have their pets vaccinated, vets will give one vaccine, such as the rabies shot, in one leg, then give the feline leukemia (FeLV) vaccine in the opposite leg. This way, if an aggressive tumour occurs, we can amputate the leg to save the cat's life.

The adjuvant within the vaccination is usually aluminum. This ingredient helps to keep the killed virus within the area where the injection was given for a short time so the body can develop an immune response. By keeping the killed virus in one small area, it makes it easier for the cat to develop a localized inflammation, which can stimulate the development of the sarcoma. Cat owners should discuss modifying their cat’s vaccination schedule with the vet.

The third cause is a mutant form of FeLV, called feline sarcoma virus or FeSV, which can lead to fibrosarcoma. This occurs in younger cats, who develop multiple tumors.

If the vet suspects a fibrosarcoma, they will run several tests. First, they will give the cat a full physical exam, from head to tail, so they can rule out any other causes of the lumps. Making an early diagnosis while the cancerous lump is still small gives the cat a higher chance of recovery and survival. Early detection also allows the vet to prescribe more options that give the cat a more positive outcome.

They will order routine testing, such as a biochemical profile, urinalysis and a complete blood count. These tests allow the vet to rule out other illnesses and to assess the cat's overall health.

Next, the vet will order X-rays or a CT scan, which allow them to see the lump and whether the cancer has spread to other parts of the cat’s body. An X-ray shows a fibrosarcoma as a soft tissue mass.

Once the vet begins to narrow their diagnosis down, they will do a fine-needle aspiration or biopsy of the lump so the cells can be examined under a microscope. 

Finally, the vet does a FeLV test. This is a blood test that will allow them to determine if the fibrosarcoma has developed because of FeSV.

Once the vet has made a diagnosis, the pet owner will need to work with them to start cancer treatment and begin an at-home treatment regimen so the cat has a better chance of survival.

Treatment options depend on where in the cat’s body the cancer is located. It’s much easier to treat cancer that has not spread to other organs, because they spread with nearly invisible tentacles. This makes complete eradication of the cancer even more difficult because, if any cancer cells remain in the cat’s body, new cancers can develop.

Surgery

Depending on where the cancer is located, the vet may suggest surgery to remove the cancer, along with the removal of some of the healthy tissue. Limb amputation may be necessary.

Radiation

Post-surgery, the vet may prescribe radiation, which helps to destroy any remaining cancerous cells. Radiation treatment begins about two weeks post-surgery.

Chemotherapy 

Chemotherapy may also be prescribed. This can begin before surgery so the tumor can be shrunk, making removal easier. After surgery, chemo may be given again so remaining cancer cells can be killed off. While humans are likely to lose their hair, chemo given to a cat doesn’t lead to them losing their hair. Instead, they will be tired, sleeping more than usual for a day or two. 

The vet may also recommend a combination of surgery, radiation therapy, and chemotherapy. When a cat with fibrosarcoma has undergone chemo, it may survive for two or three years after diagnosis and treatment.

The vet may opt for oral medication to treat the cancer. If the cat experiences pain symptoms, the vet prescribes pain medication. Some vets are open to complementary treatments, including immunotherapy, acupuncture or nutritional therapy.

Recovery from fibrosarcoma depends on where the tumor is located, how long it has existed in the cat, and its grade. The grade is determined by the frequency of cell division within the tumor. 

Very young cats (up to one year old) are more likely to have malignant tumors. If the cat dies from fibrosarcoma, it is likely because of the recurrence of primary site tumors. A veterinary pathologist can give the vet and cat owner a prognosis which gives the cat owner a probability of recurrence of the cancer or a metastasis of the cancer to other parts of the cat’s body.

At home, pet owners need to keep the cat from scratching, biting, licking or rubbing the tumor. If an affected area becomes ulcerated, the cat’s owner needs to keep this clean. After surgery, the cat owner should report any suture loss, swelling and bleeding to the vet.