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Last updated 8/31/2010
Vaccine-associated Fibrosarcoma in Cats
What is a vaccine-associated fibrosarcoma?
Several studies have shown a strong association between the administration of feline vaccines (eg rabies and feline
leukemia virus) and subsequent development of soft tissue sarcoma at the site of vaccination. The development of soft
tissue sarcoma at the sites of vaccine administration is estimated to occur in 1 out of 1,000-10,000 cats, and the time it
takes for the tumors to develop has been reported to range from 4 weeks to 10 years. A large study of cats in the United
States and Canada found that no single vaccine manufacturer or vaccine type is associated with the higher risk of cancer
development. The exact mechanism by which vaccination contributes to cancer development is not yet known, but it is
believed that the inflammatory reactions that occur after vaccination are responsible for the later tumor development.
Tumors that develop after vaccination are typically fibrosarcomas, but can also include other sarcoma subtypes such as
rhabdomyosarcoma, malignant fibrous histiocytoma, undifferentiated sarcoma, extraskeletal osteosarcoma, and
chondrosarcoma. Vaccine-associated sarcomas are usually more aggressive in their behavior compared to other non-
vaccine sarcomas. One study of 100 cats diagnosed with vaccine-associated sarcoma reported that of these, 60% of cats
had high grade tumors (highly aggressive) compared to only 6% who had low grade tumors (mildly aggressive).
How is vaccine-associated fibrosarcoma diagnosed?
The diagnostic tests for vaccine-associated sarcomas are similar to those described under the soft tissue sarcoma
section. Advanced imaging such as CT (computed tomography) or MRI (magnetic resonance imaging) are recommended
for vaccine-associated sarcomas to evaluate the extent of the disease in order to plan an appropriate treatment strategy.
Do these tumors cause pain?
It is imperative that pets with cancer are provided with pain medication to relieve discomfort caused by the disease as well
as by the treatments. To learn more, please visit the Cancer Pain Management section.
What food should be fed to pets with cancer?
Pets with cancer need to be fed diets specifically designed to support a cancer patient. To learn more, please visit the
Cancer Nutrition section.
What are the treatment options?
Vaccine-associated sarcomas are very invasive tumors and require an aggressive treatment including aggressive surgery
with or without radiation therapy.
Surgery
The surgical treatment removes not only the tumor itself, but also some of the surrounding healthy tissues to ensure that
no or very few cancer cells are left behind. When such healthy tissues are not removed, the tumor usually grows back in
2.5 months. When the surrounding tissues are removed, it takes on the average about 1 year for the tumor to grow back.
The first surgical attempt to remove vaccine-associated sarcoma has the best chance to control the tumor, therefore, it
should be performed by an experienced board certified surgeon. For tumors located on the limbs, amputation is usually
required to achieve sufficient control of the tumor.
Surgery and radiation therapy
Although surgery removes all of the visible tumor, if there are any cancer cells left behind, the tumor will grow back - a
process called local recurrence. Due to the high risk of local recurrence for vaccine-associated sarcomas, radiation
therapy is recommended following surgery to attempt to kill any remaining cancer cells. The timing of surgery and
radiation therapy remains controversial among veterinarians. Administering radiation therapy prior to surgery has the
advantages of reducing the tumor size for subsequent surgery and decreasing the risk of spreading cancer cells
throughout the surgical site. Its main disadvantage, however, is that it increases the risk of surgical complications.
Administering radiation after surgery may provide better tumor control since individual cancer cells are easier to kill than
an entire mass, however, surgery increases the size of the area that will need to be irradiated. Radiation therapy should
be scheduled within 10-14 days of surgery to maximize the benefit of this combinatorial approach.
Chemotherapy
The benefit of chemotherapy to treat vaccine-associated sarcoma is not well established. Some responses were observed
in cats treated with chemotherapy drugs doxorubicin, mitoxantrone, vincristine, and paclitaxel, but these responses were
usually short-lived. Administering chemotherapy after surgery/radiation therapy does not significantly affect the cats'
overall survival but may prolong the time the tumor will take to grow back.
Are there any clinical trials investigating new treatments?
There are only a few available clinical trials investigating new treatments for vaccine-associated sarcomas in cats. To
learn more about clinical trials open to enrollment in the United States, please visit the Clinical Trials for Vaccine-
associated Sarcoma section. To learn more about veterinary clinical trials in general, please visit the Pet Clinical Trials
section.
To help Pet Cancer Center conduct more vaccine associated fibrosarcoma cancer clinical trials across the United States
in order to make novel and more efficacious therapies available to pets, please
What is the prognosis?
The prognosis for cats with vaccine-associated sarcoma treated by surgery alone is poor. Despite aggressive surgeries,
65% of cats develop new tumors one year after surgery and 91% after two years. The outcome is better for cats who are
treated with one initial aggressive surgery compared to those who are treated with multiple conservative surgeries. The
median average survival time following complete surgical tumor removal is approximately 16 months. Combining radiation
therapy with surgery improves the overall survival to 23 months but local recurrence still occurs in 28-45% of cats.
Metastasis (spread) to other organs such as the lungs has been reported for 12-26% of cats, with a median time to
metastasis of 265 days.
Additional online resources:
Vaccine-Associated Feline Sarcoma Task Force
http://www.pubmedcentral.nih.gov/picrender.fcgi?artid=340241&blobtype=pdf
http://www.vin.com/VINDBPub/SearchPB/Proceedings/PR05000/PR00109.htm
http://www.dvmnews.com/dvm/data/articlestandard//dvm/482003/77544/article.pdf
http://en.wikipedia.org/wiki/Vaccine-associated_sarcoma
Sources:
Several studies have shown a strong association between the administration of feline vaccines (eg rabies and feline
leukemia virus) and subsequent development of soft tissue sarcoma at the site of vaccination. The development of soft
tissue sarcoma at the sites of vaccine administration is estimated to occur in 1 out of 1,000-10,000 cats, and the time it
takes for the tumors to develop has been reported to range from 4 weeks to 10 years. A large study of cats in the United
States and Canada found that no single vaccine manufacturer or vaccine type is associated with the higher risk of cancer
development. The exact mechanism by which vaccination contributes to cancer development is not yet known, but it is
believed that the inflammatory reactions that occur after vaccination are responsible for the later tumor development.
Tumors that develop after vaccination are typically fibrosarcomas, but can also include other sarcoma subtypes such as
rhabdomyosarcoma, malignant fibrous histiocytoma, undifferentiated sarcoma, extraskeletal osteosarcoma, and
chondrosarcoma. Vaccine-associated sarcomas are usually more aggressive in their behavior compared to other non-
vaccine sarcomas. One study of 100 cats diagnosed with vaccine-associated sarcoma reported that of these, 60% of cats
had high grade tumors (highly aggressive) compared to only 6% who had low grade tumors (mildly aggressive).
How is vaccine-associated fibrosarcoma diagnosed?
The diagnostic tests for vaccine-associated sarcomas are similar to those described under the soft tissue sarcoma
section. Advanced imaging such as CT (computed tomography) or MRI (magnetic resonance imaging) are recommended
for vaccine-associated sarcomas to evaluate the extent of the disease in order to plan an appropriate treatment strategy.
Do these tumors cause pain?
It is imperative that pets with cancer are provided with pain medication to relieve discomfort caused by the disease as well
as by the treatments. To learn more, please visit the Cancer Pain Management section.
What food should be fed to pets with cancer?
Pets with cancer need to be fed diets specifically designed to support a cancer patient. To learn more, please visit the
Cancer Nutrition section.
What are the treatment options?
Vaccine-associated sarcomas are very invasive tumors and require an aggressive treatment including aggressive surgery
with or without radiation therapy.
Surgery
The surgical treatment removes not only the tumor itself, but also some of the surrounding healthy tissues to ensure that
no or very few cancer cells are left behind. When such healthy tissues are not removed, the tumor usually grows back in
2.5 months. When the surrounding tissues are removed, it takes on the average about 1 year for the tumor to grow back.
The first surgical attempt to remove vaccine-associated sarcoma has the best chance to control the tumor, therefore, it
should be performed by an experienced board certified surgeon. For tumors located on the limbs, amputation is usually
required to achieve sufficient control of the tumor.
Surgery and radiation therapy
Although surgery removes all of the visible tumor, if there are any cancer cells left behind, the tumor will grow back - a
process called local recurrence. Due to the high risk of local recurrence for vaccine-associated sarcomas, radiation
therapy is recommended following surgery to attempt to kill any remaining cancer cells. The timing of surgery and
radiation therapy remains controversial among veterinarians. Administering radiation therapy prior to surgery has the
advantages of reducing the tumor size for subsequent surgery and decreasing the risk of spreading cancer cells
throughout the surgical site. Its main disadvantage, however, is that it increases the risk of surgical complications.
Administering radiation after surgery may provide better tumor control since individual cancer cells are easier to kill than
an entire mass, however, surgery increases the size of the area that will need to be irradiated. Radiation therapy should
be scheduled within 10-14 days of surgery to maximize the benefit of this combinatorial approach.
Chemotherapy
The benefit of chemotherapy to treat vaccine-associated sarcoma is not well established. Some responses were observed
in cats treated with chemotherapy drugs doxorubicin, mitoxantrone, vincristine, and paclitaxel, but these responses were
usually short-lived. Administering chemotherapy after surgery/radiation therapy does not significantly affect the cats'
overall survival but may prolong the time the tumor will take to grow back.
Are there any clinical trials investigating new treatments?
There are only a few available clinical trials investigating new treatments for vaccine-associated sarcomas in cats. To
learn more about clinical trials open to enrollment in the United States, please visit the Clinical Trials for Vaccine-
associated Sarcoma section. To learn more about veterinary clinical trials in general, please visit the Pet Clinical Trials
section.
To help Pet Cancer Center conduct more vaccine associated fibrosarcoma cancer clinical trials across the United States
in order to make novel and more efficacious therapies available to pets, please
What is the prognosis?
The prognosis for cats with vaccine-associated sarcoma treated by surgery alone is poor. Despite aggressive surgeries,
65% of cats develop new tumors one year after surgery and 91% after two years. The outcome is better for cats who are
treated with one initial aggressive surgery compared to those who are treated with multiple conservative surgeries. The
median average survival time following complete surgical tumor removal is approximately 16 months. Combining radiation
therapy with surgery improves the overall survival to 23 months but local recurrence still occurs in 28-45% of cats.
Metastasis (spread) to other organs such as the lungs has been reported for 12-26% of cats, with a median time to
metastasis of 265 days.
Additional online resources:
Vaccine-Associated Feline Sarcoma Task Force
http://www.pubmedcentral.nih.gov/picrender.fcgi?artid=340241&blobtype=pdf
http://www.vin.com/VINDBPub/SearchPB/Proceedings/PR05000/PR00109.htm
http://www.dvmnews.com/dvm/data/articlestandard//dvm/482003/77544/article.pdf
http://en.wikipedia.org/wiki/Vaccine-associated_sarcoma
Sources:
- Withrow Stephen J, and David M. Vail. Small Animal Clinical Oncology. St Louis: Saunders Elsevier, 2007.
- Morrison Wallace B. Cancer in Dogs and Cats: Medical and Surgical Management. Baltimore: Williams&Wilkins,
1998.
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