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Vaccine
Associated Sarcomas in Cats (VAS)
Dr.
Gail Mason, DVM, MA, DACVIM
Kathi Smith, RVT, Internal Medicine
& Oncology Technician
Vaccinating domestic cats against serious infectious
disease is an important step in good quality
health care. The diseases that are vaccinated
for can cause serious illness and/or death.
Vaccination against rabies is an important pet
health, public health, and legal issue as well.
However, due to statistical association between
some vaccines and subsequent sarcoma development
which was noted over the last decade, vaccine
types and protocols are under heavy scrutiny.
Sarcomas
Injection
site sarcomas, as the name implies, can develop
in areas of the body where vaccination has taken
place. This typically is between the animal's
shoulder blades (interscapular) or on a hind
limb. These tumors are aggressive in nature
and are associated with significant tissue inflammation
and decay. They tend to infiltrate the normal
tissues with malignant tendrils making surgical
excision difficult. Although they are considered
to be in the class of "soft tissue sarcomas,"
they have a higher metastatic rate than other
tumors of this class.
Staging
Current
recommendations suggest that masses noted at
vaccine sites which are present 3 or more months
post-vaccinations, are greater than 2cm or are
rapidly growing should be dealt with in a timely
fashion. An incisional biopsy can confirm a
VAS. Matastasis can occur to local lymph nodes
and to the lungs.
Staging
of the patient to evaluate the extent of the
disease may include:
• Chest radiographs (x-rays)
• Abdominal radiographs
•
Routine
blood screening
• Ultrasonography or a CT scan
Treatment
Patients
have longer survival times when an aggressive,
initial resection is performed and is followed
by radiation therapy. If the tumor is located
on a limb, it may be necessary to perform a
limb amputation. As unpleasant as this idea
is, it is well-documented that patient recovery
is rapid and quality of life can be excellent.
Chemotherapy has also been used in the treatment
of VAS but its exact efficiency remains to be
determined. Most published veterinary medical
reports have described use of either doxorubicin
and/or carboplatin.
Prognosis
Unfortunately,
cats with VAS may have a guarded to poor long
term prognosis. Remission times are variable,
but most often reported as being between 8 months
to 1.6 years. Initial aggressive and complete
resection appear to positively influence outcomes
and longer, excellent quality remissions have
been documented.
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