Lymphoma in Pets

Lymphoma is a cancer of a specific white blood cell called the
lymphocyte. Lymphocytes are found throughout the body in blood
and tissues and act to protect the body from infec-tion.
Lymphocytes are the major cells found in lymph nodes or
“glands.” In lymphoma, the cancer cells invade and destroy
normal tissues. The most common site for lymphoma is the lymph
nodes, but lymphoma cells, like lymphocytes, can grow anywhere
in the body. In most dogs and cats with lymphoma, the cancer
cells are present in multiple lymph nodes and tissues.

Chemotherapy is the treatment of choice for almost every dog and
cat with lymphoma. Chemotherapy is the administration of drugs
by injection or by mouth to kill cancer cells. The
chemotherapeutic drug circulates throughout the body. This is
important for lymphoma because the cancer cells are in many
places at once. Surgery and radiation therapy are less useful in
lymphoma because these treatment methods attack cancer cells at
only one site.

The goal of chemotherapy for animals with lymphoma is to induce
a complete “remission” by killing most of the cancer cells.
“Remission” means that all symptoms of the cancer have
temporarily disappeared. Animals with Iymphoma that are in
complete remission look like normal animals by all tests. They
do not have any signs of cancer, and all masses or lumps have
disappeared. They eat, drink, and run just as they did before
they developed cancer. Some of the cancer cells do survive in an
animal in complete remission, but the numbers are too small to
detect. Eventually, these few cells will grow and the cancer
will become evident again. When this happens the animal is said
to be “out of remission.” Sometimes a second remission can be
achieved with additional chemotherapy. Eventually, the cancer
cells will become resistant or insensitive to all drugs and
cause the dog or cat to die.

Veterinarians use many different drugs and drug combinations
called “protocols” to treat lymphoma in dogs and cats. No one
knows the “best” treatment, and many protocols give similar
results. In general, the longest survival times are reported for
protocols that use a combination of drugs and include more
expensive drugs.

Although chemotherapy does not cure dogs and cats with Iymphoma,
in most it does extend the quantity and quality of life. About
80 to 90 per cent of dogs with lymphoma attain a complete
remission with an average survival of 1 year, and 25 per cent of
dogs live 2 years. For cats, the remission rate is lower, with
about 50 per cent attaining a complete remission, but cats who
achieve only partial remission also feel better according to
owners. The average survival for cats is 7 to 10 months.

Veterinarians use chemotherapy to give dogs and cats with
lymphoma a good quality of life with minimal side effects. Most
dogs and cats with lymphoma feel good even though they are
receiving chemotherapy. The potential for side effects does
exist, however, and varies with the protocol used. The most
common side effects include decreased energy, decreased
appetite, vomiting, and diarrhea.

Occasionally, more severe side effects occur, and in rare cases
an animal receiving chemotherapy will die as a result of
treatment. Unfortunately, the only way to know whether an animal
is going to have a drug reaction is to give the drug. Some
animals never get sick during chemotherapy, but others are very
sensitive to the drugs. If your pet has a serious reaction, the
drugs or doses your pet receives may be individually adjusted to
maintain a good quality of life.

As an owner, you can help your pet with lymphoma by watching the
pet closely after each treatment. Chemotherapy will suppress
your pet’s immune system and make him or her more susceptible to
infections. These infections generally arise from bacteria that
normally live in the intestinal tract and on the skin, not from
the environment. Signs of an infection may include loss of
appetite, vomiting, diarrhea, decreased activity, or depression.
Phone your veterinarian immediately if your pet appears ill
while receiving chemo-therapy. These signs are usually only
brief reactions to the drugs, but prompt treatment can often
prevent more serious side effects from developing.

The above is general veterinary information. Do not begin
any course of treatment without consulting your regular
veterinarian. All animals should be examined at least once every
12 months.