A sarcoma is a cancer of the connective and
soft tissues. Sarcomas are not a new form of cancer in cats. But in 1991, veterinarians began to notice a
higher than expected number of sarcomas occurring in places where vaccines are commonly injected.
Subsequently, an association between vaccine administration and sarcoma
development has been established. FeLV and rabies virus vaccines have more
frequently been implicated in sarcoma development than have other vaccines.
Both subcutaneous and intramuscular sites have been affected. Injections other
than vaccines may also be implicated.
The increased appearance of these sarcomas roughly coincided with the change
from using a modified-live rabies virus vaccine to an adjuvanted killed virus
vaccine. At about the same time, an aluminum-adjuvanted FeLV vaccine was
introduced. Adjuvants are added to vaccines to increase the immune
response-especially in vaccines that use killed versions of a virus. Adjuvants
in general, and aluminum adjuvants in particular, were therefore thought to be
the culprit. However, researchers are no longer certain this is the case. It is
believed that these vaccines cause some kind of inflammation at the vaccination
site that, in some cases, is associated with sarcoma development, but an exact
link has not been proven.
Shedding is a cat’s natural process of losing dead hair. Outdoor cats may lose more hair in the spring and fall and retain more fur in the winter, while indoor cats can shed all year round. Regularly grooming your cat and vacuuming hair from your house should minimize the inconvenience of shedding. However, if you see bald patches in your cat’s fur or notice a significant loss of hair, the underlying cause may be a health-related problem and should be investigated by a veterinarian.
Nonetheless, vaccine manufacturers are developing recombinant vaccines that
do not use adjuvant and that cause less inflammation at the vaccination site.
Many modified-live virus vaccines are available for other viral diseases and
some of them do not contain adjuvant. New vaccination guidelines try to
minimize the number of injections given over a cat’s lifetime, as well, and
also recommend specific sites on the body for injections to be given.
It’s important to remember that vaccine-associated sarcoma is still a very
rare form of cancer. The occurrence rate varies from 1 in 1,000 to 1 in 10,000.
The wide range seems to be associated with a genetic predisposition to this
problem in certain cats and lines of cats. For instance, some geographic areas
show an increased rate.
These cancers may show up months or even years after a vaccination. Although
a fair number of cats have a small lump after getting a vaccination, the lump
should be gone within a month. If it is not, have the cat examined by a