Canine Lymphosarcoma (Lymphoma, LSA)
Incidence/cause
LSA, a tumor caused by a cancerous proliferation of lymphocytes (cells
that normally function in the immune system), is one of the most common
tumors seen in dogs. It affects dogs of any breed and age, although most
dogs will be middle-aged or older at the time of diagnosis; Golden
retrievers are considered a breed at increased risk of developing LSA. The
cause of LSA in dogs, as is true for most canine tumors, is not known.
What you might see/ Clinical presentation
The presentation of dogs with LSA is highly variable as lymphocytes can
be found in virtually any organ in the body. Nonetheless, the most common form
(referred to as stages) of LSA causes a non-painful enlargement of one or more
lymph nodes that can be seen or felt from the body surface. Occasionally, a
lymph node becomes large enough to impair function (obstruction of blood flow or
airway, for example). Other forms of LSA can involve the liver, spleen, bone
marrow and gastrointestinal tract, skin or nervous system (and other organs) and
the clinical signs will reflect the organ system involved (e.g. vomiting or
diarrhea with gastrointestinal forms; weakness or pale mucous membranes and
others that reflect impaired production of blood cells from the bone marrow);
many dogs will simply feel ill (lose appetite, become lethargic) with any of the
different forms. In some dogs, lymph node enlargement is an incidental finding
when an otherwise healthy-appearing dog is seen by a veterinarian for an
unrelated reason (e.g. vaccination).
Lymph node staging
Stage I: single lymph node enlarged
Stage II: multiple nodes enlarged on either the front half or back half
of the body
Stage III: multiple nodes enlarged on both front and back halves of body
Stage IV: involvement of the liver and/or spleen
Stage V: bone marrow involvement, or involvement of other organs (e.g.
gastrointestinal, skin, nervous system)
Each numbered stage can be further divided into substages, of which
there are two: a and b. Patients with substage a feel well while patients with
substage b are ill.
Biological behavior of LSA
LSA is viewed as a systemic disease, and as such is not really viewed to
"spread" to other organs. This tumor is not generally viewed as a curable tumor
in dogs, although occasional dogs will experience what seems to be a cure with
appropriate treatment (see below). A dog can start with one stage of the disease
and progress over time to another (usually more advanced) stage of LSA.
Clinical staging (determination of the extent of the tumor)
Because of the organs that LSA commonly involves, staging a dog with a
LSA can involve aspiration of one or more lymph nodes, 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. Often, obtaining
blood for a complete blood count and biochemical profile, and a urinalysis will
be 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 are the same for either type.
Treatment options
The mainstay of treatment of LSA is administration of chemotherapy
drugs; 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. In some dogs with very localized disease, surgery or radiation
therapy can play a role in treatment, although chemotherapy is still often
recommended in these cases.
Prognosis
The prognosis of dogs with LSA is highly variable, and depends on the
clinical stage (ill dogs fare more poorly than dogs that feel well, and dogs
with Stage V disease are generally considered to have a poorer prognosis), the
type of tumor (dogs with B-cell LSA usually do better than dogs with T-cell
LSA). Most dogs treated with chemotherapy will experience a remission, a period
in which there is no detectable cancer and the dog feels well. Remission times
are variable, but most dogs with the lymph node forms of LSA will have initial
remissions lasting in the range of 6-9 months before evidence of the tumor is
seen again; second remissions can be achieved in many of these dogs, but any
subsequent remission is expected to be shorter in duration than the first
remission. Survival times for most dogs treated with combination chemotherapy
protocols are in the range of approximately 1 year. And even though an
individual dog will have received a lot of chemotherapy over that year, their
quality of lfe is generally very good. Statistics, while useful, can never
predict how an individual dog will fare with or without specific treatment.
Future treatment options:
New protocols are tried with great regularity in canine 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 dogs 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 dog
lymphoma, which could recognize all dog 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 most dogs tolerate chemotherapy very well with minimal impact on
their quality of life. If you notice fast growing lumps on your dog that seem to
be in the area of the major joints (at the neck, in front of the shoulders, in
the armpits, at the back of the knees or in the groin) have your dog examined
soon by a veterinarian even if he feels well. Remember, lower stage disease, and
dogs that feel well, will do better with treatment than dogs that are ill and/or
have more advanced disease.
Other helpful sites
http://www.caninecancerawareness.org/html/CanineCancerLymphoma.html
