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As feline leukemia
virus infections become less common, the gastrointestinal
form of this cancer becomes more common.
Lymphoma is the most commonly diagnosed cancer in cats, accounting for
about 33% of all tumors in cats. It arises from lymphoid tissue, and may
involve any organ. Cats of any age can be affected. A few studies have
found Siamese cats to be at higher risk of developing lymphoma, as well
as male cats. The term lymphosarcoma is synonymous with lymphoma,
however, lymphoma has become the preferred term.
Lymphoma is commonly divided into four groups: gastrointestinal
(stomach, small intestine, large intestine), mediastinal (within the
chest cavity), multicentric (the lymph nodes, liver and spleen), and
extranodal (other organs, such as the eye, kidney, bone marrow, nervous
system, skin, lungs, and nasal cavity).
Viruses may play a role in the development of lymphoma in cats. The
feline immunodeficiency virus (FIV) is associated with an increased risk
of lymphoma. Cats infected with FIV are 5.6 times more likely to develop
lymphoma compare to FIV-negative cats. Infection with the feline
leukemia virus (FeLV) dramatically increases the risk of developing
lymphoma; FeLV-positive cats are 62 times more likely to develop
lymphoma than their negative counterparts.
As the prevalence of FeLV infection has decreased over the last 20
years, the presentation and anatomic site of lymphoma has changed.
Before 1980, the majority of cats with lymphoma were under the age of 7,
infected with FeLV, and had the mediastinal (chest) form of the disease.
With the advent of widespread testing and vaccination for FeLV, the
gastrointestinal form has become the most common site for lymphoma. It
now occurs most commonly in older cats (greater than 10 years), and most
are FeLV-negative.
Gastrointestinal lymphoma usually involves the small intestine. The
stomach and colon are less likely to be affected. The average age of
cats with GI lymphoma is 9 to 13 years.
The most common clinical signs of GI lymphoma are decreased appetite and
weight loss. Vomiting occurs in about 50% of cases, and diarrhea in
about 30%.
Biopsies are required to obtain a definitive diagnosis of GI lymphoma.
Biopsy specimens can be obtained either by endoscopy, in which a long
snake-like tube with a camera on the end is inserted in the cat’s mouth,
and then advanced into the stomach and small intestine, or by abdominal
surgery. Surgical biopsies are usually of better quality, however, the
procedure is invasive. Endoscopy is much less invasive, but there is a
possibility that the samples obtained will be non-diagnostic. Both
procedures require general anesthesia.
Once a diagnosis is achieved, the lymphoma is categorized into one of
two general types: low grade (also called “small cell” or “lymphocytic”)
or high grade (also called “large cell” or “lymphoblastic”). The type of
lymphoma is significant in terms of prognosis. Low grade lymphoma has a
significantly better prognosis than high grade lymphoma.
Chemotherapy is the treatment of choice, as lymphoma is the considered
the most chemotherapy-responsive cancer. Combination chemotherapy, in
which several drugs are administered sequentially, is the primary method
of treatment. In cases where the lymphoma is causing a complete or
partial intestinal obstruction, or an intestinal perforation, surgery
may be necessary to treat this immediate problem, followed by
chemotherapy.
The prognosis for gastrointestinal lymphoma varies, depending on type.
Cats with high grade lymphoma are less likely to go into remission
compared to those with low grade lymphoma. The median survival time,
with chemotherapy, for high-grade lymphoma is only 2.7 months. Cats with
low-grade lymphoma, fare much better. Median survival of 17 months has
been reported, and it is not uncommon for cats to survive two years or
longer.
Updated 7/2/07 |
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