| Vaccine associated fibrosarcomas are
tumors that arise at sites where cats have been vaccinated. They are
most commonly associated with the rabies vaccine and the vaccine for
feline leukemia virus. We continue to give these vaccines because of
the relatively high risk of contracting these diseases and the relatively
low risk of developing a fibrosarcoma. The incidence of these tumors
is not known, but is reported to be about 1 in 10,000. Fibrosarcomas
tend to be very aggressive locally, and can also metastasize (spread
to other areas of the body).
The first attempt at treatment is thought to have the best chance of
curing or slowing the disease, although it is possible to treat disease
recurrence. Treatment generally involves combinations of surgery, radiation
therapy and chemotherapy. It is necessary to determine the extent of
the cancer in order to determine which treatment option is best for
your cat.
A thorough physical exam, chest radiographs ("x-rays") and
blood work are all part of the initial work-up. Although pulmonary metastasis,
or the spread of the tumor to the lungs, occurs only about 10-25% of
the time, it changes the prognosis and treatment options available for
your cat. A CT scan, which allows careful evaluation of the tumor and
the tissues around it, is usually required as part of the diagnostic
plan. If a biopsy has not been done one will be done at the same time
as the CT scan
.
With the information obtained from the CT scan we will be able to formulate
a treatment plan. If the tumor is very small or non-invasive, surgery
alone may be recommended. In other cases we may recommend radiation
therapy followed by surgery, or we may recommend chemotherapy alone,
which tends to be very well tolerated by cats. If surgery or radiation
therapy followed by surgery is recommended we will offer follow-up chemotherapy
to try to decrease the likelihood that lung metastasis will occur.
If your cat has a recurrence of a fibrosarcoma, the diagnostic procedures
will be very similar. Again, imaging the tumor with radiographs and
a CT scan will help us determine the extent of the tumor and help us
to formulate a treatment plan for your cat.
This handout is designed to answer some of the basic questions relating
to feline vaccine associated fibrosarcoma. Your cat's particular situation
may vary. If you have any questions please ask us; we will be happy
to answer them to the best of our ability.
VMTH Oncology Service |