Feline Lymphosarcoma (Lymphoma, LSA)
Incidence/Cause
Lymphosarcoma is a tumor caused by a cancerous proliferation of
lymphocytes or, cells that normally function in the immune system.
This is a very common tumor in cats and can present in a variety of
ways. At one time, feline leukemia virus (FeLV) was a leading cause
of LSA in cats and typically young cats were infected. Now that the
incidence of FeLV has decreased cats still develop LSA but it is
generally older cats and different forms. The Feline aids virus
(FIV) has also been shown to increase the risk of a cat developing
LSA six times over a non-infected cat. Any breed of cat can develop
LSA. The cause of the disease unrelated to FeLV or FIV is unknown
although environmental smoke exposure has been found to increase a
cat’s risk of LSA, and a possible link to long standing inflammatory
disease has long been theorized.
What you might see/ Clinical presentation
Cats with LSA present with a variety of signs because lymphocytes
can be found in nearly every organ in the body. Also, cats seem to
have more forms of LSA in atypical locations or not in normal
lymphoid tissues, as compared to other species. Most species
including man present with large lymph nodes, but this is a rare
form of LSA in cats. Young cats typically present for masses in the
chest cavity and owners notice signs of difficulties breathing or
vomiting of food. Older cats develop the tumor in their intestines
quite commonly and owners may notice signs such as weight loss,
diarrhea or vomiting. They also can however develop LSA in areas as
diverse as the nasal passages, kidneys, spinal cord, liver, eyes, or
a single lymph node, and the signs seen will be more specific for
the organ affected. Because cats present with such a variety of
organs affected there is no valid staging system for feline LSA and
a cat diagnosed with the disease will more likely be staged by the
organ affected (eg. gastrointestinal LSA, mediastinal LSA etc.)
Biological behavior of LSA
Even though many cats present with only a single site of
involvement, LSA is viewed as a systemic disease. Lymphocytes in
their normal functioning capacity travel throughout the body and as
a cancer the disease is also moving though not in a classical sense
"metastasizing". Even if a tumor diagnosed as LSA has been
surgically removed the disease is not gone.
Clinical staging (determination of the extent of the tumor)
Because of the organs that LSA commonly involves, staging a cat with
a LSA can involve aspiration of one or more lymph nodes or masses,
thoracic radiographs abdominal radiographs or ultrasound (to look
for big nodes in the abdomen and to look at the liver and spleen),
or bone marrow examination. Obtaining blood for a complete blood
count and biochemical profile, FeLV, FIV, and a urinalysis is always
advised as these can help assess overall health and provide
information that potentially influences treatment recommendations.
Sometimes, special stains to determine if the LSA is of B-cell or
T-cell origin (B-cells and T-cells are specific types of
lymphocytes) are recommended because of prognostic significance,
although treatment recommendations may be the same for either type.
Staging the disease can be critical in choosing treatment protocols.
Treatment options
Chemotherapy should always be considered a critical part of the
treatment for LSA. The best responses in terms of length of tumor
control and survival are generally seen with protocols that entail
administration of more than one chemotherapy drug, although there
are approaches that involve administration of a single drug.
Chemotherapy drugs commonly used include: doxorubicin, vincristine,
cyclophosphamide, prednisone, and L-Aspariginase, but many others
are also used. Some protocols are very aggressive and relatively
short (six month total) and others are less aggressive but extend
for one to two years. The decision of which protocol is to be used
does depend on the results of the tumor biopsy (not all LSA is the
same) and the staging results. Thankfully, the chemotherapy
generally act quickly so that even cats with sever signs can have
relief fairly soon after starting therapy (sometimes as quickly as
24 hours). Surgery is sometimes recommended as a part of the
treatment but this is usually either to reach a diagnosis or to
remove a potentially life threatening problem (for example
intestinal rupture due to a tumor mass). Surgery is never curative
and should always be followed by chemotherapy to best extend the
cat’s life. Radiation can also play a role in the treatment of very
localized LSA. The primary site most benefiting from radiation
therapy is nasal LSA.
Prognosis
Cats with LSA have unpredictable responses and survivals. Depending
on the site of the tumor, mean survivals with chemotherapy range
from 6-9 months. The problem is that this is only an average and
most cats tend to do either much worse or much better. Young cats,
FeLV negative, with mediastinal LSA are quite regularly cured with
chemotherapy; cats with LSA in their central nervous system
typically have a bad prognosis, but most other forms of LSA in cats
have unpredictable outcomes. Generally it is best to at least try a
chemotherapy protocol because it may be the only way to see how an
individual cat will do. Cats often do not enjoy receiving
chemotherapy, but veterinary oncologist try hard to make the regime
tolerable for each feline patient even if it means modifications in
a protocol.
Future treatment options
New protocols are tried in feline lymphoma but results have been
similar with each drug regime investigated. Most likely our
survivals will always be similar until we either accept greater
toxicity (meaning most cats will be very sick from the treatment and
some may even die), or a completely novel treatment is invented.
Using half or whole body radiation therapy may prove helpful. The
development an antibody specific for cat lymphoma, which could
recognize all cat lymphomas and yet no normal lymphocytes, and be
attached to a toxin or other cell killing mechanism, is a far off
dream.
Key points
LSA is one of the most chemotherapy-responsive tumors seen in
veterinary medicine and cats can tolerate chemotherapy relatively
well, or protocols can be modified so that an individual cat can
maintain a good quality of life while on chemotherapy. Unfortunately
we have few strong predictors of which cats will have good responses
to chemotherapy and long survivals, and survival is therefore
difficult to estimate at the outset. Often the only way to know how
a cat will respond to treatment, is to start treatment.
Other helpful sites
http://www.caninecancerawareness.org/CanineCancerLymphoma.html
Last Edited: Dec 07, 2007 3:27 PM
