Issue Description Lymphoma is one of the most common malignant
tumors to occur in dogs. The cause is genetic, but there also
suspected environmental factors involved. Other Names Lymphosarcoma
Commonly Affected Breeds
German Shepherd Dog
Golden Retriever - The Golden Retriever is especially susceptible
to developing lymphoma, with a lifetime risk of 1:8.
Classification The cancer is classified into low and high
grade types. Classification is also based on location. The four
location types are multicentric, mediastinal, gastrointestinal, and
extranodal (involving the kidney, central nervous system, skin, heart,
or eye). Multicentric lymphoma, the most common type (by greater than
80 percent), is found in the lymph nodes, with or without involvement
in the liver, spleen, or bone marrow. Mediastinal lymphoma occurs in
the lymph nodes in the thorax and possibly the thymus.
Gastrointestinal lymphoma occurs as either a solitary tumor or diffuse
invasion of the stomach or intestines, with or without involvement in
the surrounding lymph nodes, liver or spleen. Classification is
further based on involvement of B-lymphocytes or T-lymphocytes.
Approximately 70 percent are B-cell lymphoma. Cutaneous lymphoma can
be classified as epitheliotropic (closely conforming to the epidermis)
or non-epitheliotropic. The epitheliotropic form is typically of
T-cell origin and is also called mycosis fungoides. The
non-epitheliotropic form is typically of B-cell origin.
Symptoms General signs and symptoms include depression,
fever, weight loss, loss of appetite, and vomiting. Lymphoma is the
most common cancerous cause of hypercalcemia (high blood calcium
levels) in dogs. It can lead to the above signs and symptoms plus
increased water drinking, increased urination, and cardiac
arrhythmias. Hypercalcemia in these cases is caused by secretion of
parathyroid hormone-related protein.
presents as painless enlargement of the peripheral lymph nodes. This
is seen in areas such as under the jaw, the armpits, the groin, and
behind the knees. Enlargement of the liver and spleen causes the
abdomen to distend. Mediastinal lymphoma can cause fluid to collect
around the lungs, leading to coughing and difficulty breathing.
Hypercalcemia is most commonly associated with this type.
Gastrointestinal lymphoma causes vomiting, diarrhea, and melena
(digested blood in the stool). Low serum albumin levels and
hypercalcemia can also occur.
Lymphoma of the skin is an
uncommon occurrence. The epitheliotropic form typically appears as
itchy inflammation of the skin progressing to nodules and plaques. The
non-epitheliotropic form can have a wide variety of appearances, from
a single lump to large areas of bruised, ulcerated, hairless skin. The
epitheliotropic form must be differentiated from similar appearing
conditions such as pemphigus vulgaris, bullous pemphigoid, and lupus
Signs for lymphoma in other sites depend on
the location. Central nervous system involvement can cause seizures or
paralysis. Eye involvement, seen in 20 to 25 percent of cases, can
lead to glaucoma, uveitis, bleeding within the eye, retinal
detachment, and blindness. Lymphoma in the bone marrow causes anemia,
low platelet count, and low white blood cell count.
Diagnosis Biopsy of affected lymph nodes or organs
confirms the diagnosis, although a needle aspiration of an affected
lymph node can increase suspicion of the disease. X-rays, ultrasound,
blood analysis, and bone marrow biopsy reveal other locations of the
cancer. The stage of the disease is important to treatment and
Stage I - only one lymph node or lymphoid tissue in one organ
Stage II - lymph nodes in only one area of the body involved.
Stage III - generalized lymph node involvement.
Stage IV - any of the above with liver or spleen involvement.
Stage V - any of the above with blood or bone marrow involvement.
Each stage is divided into those with systemic symptoms (loss of
appetite, weight loss, etc.) and those without.
Treatment Complete cure is rare with lymphoma and
treatment tends to be palliative, but long remission times are
possible with chemotherapy. With effective protocols, average first
remission times are 6 to 8 months. Second remissions are shorter and
harder to accomplish. Average survival is 9 to 12 months. The most
common treatment is a combination of cyclophosphamide, vincristine,
prednisone, L-asparaginase, and doxorubicin. Other chemotherapy drugs
such as chlorambucil, lomustine (CCNU), cytosine arabinoside, and
mitoxantrone are sometimes used in the treatment of lymphoma by
themselves or in substitution for other drugs. In most cases,
appropriate treatment protocols cause few side effects, but white
blood cell counts must be monitored.
Allogenic stem cell
transplantation (as is commonly done in humans) has recently shown to
be a possible treatment option for dogs. Most of the basic research on
transplantation biology was generated in dogs.
When cost is
a factor, prednisone used alone can improve the symptoms dramatically,
but it does not significantly affect the survival rate. The average
survival times of dogs treated with prednisone and untreated dogs are
both one to two months. Using prednisone alone can cause the cancer to
become resistant to other chemotherapy agents, so it should only be
used if more aggressive treatment is not an option.
Isotretinoin can be used to treat cutaneous lymphoma.
Prognosis Untreated dogs have an average survival time of
sixty days. Lymphoma with a histologic high grade generally respond
better to treatment but have shorter survival times than dogs with low
grade lymphoma. Dogs with B-lymphocyte tumors have a longer survival
time than T-lymphocyte tumors. Mediastinal lymphoma has a poorer
prognosis than other types, especially those with hypercalcemia.
Clinical stage and substage have some prognostic value, with poorer
prognosis associated with Stage V disease, and with substage b
(clinical illness at time of presentation).