Lymphoma in animals is a type of cancer defined by a proliferation of malignant lymphocytes within solid organs such as the lymph nodes, bone marrow, liver and spleen. The disease also may occur in the eye, skin, and gastrointestinal tract. It is also known as lymphosarcoma.

Lymphoma in dogs

Lymphoma is one of the most common malignant tumors to occur in dogs. The cause is genetic, but there also suspected environmental factors involved,  including in one study an increased risk with the use of the herbicide 2,4-D. This risk was not confirmed in another study.

Commonly affected breeds

* Boxer
* Scottish Terrier
* Basset Hound
* Airedale Terrier
* Chow Chow
* German Shepherd Dog
* Poodle
* St. Bernard
* Bulldog
* Beagle
* Rottweiler
* The Golden Retriever is especially susceptible to developing lymphoma, with a lifetime risk of 1:8.

Signs and 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.

Multicentric lymphoma 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 erythematosus.

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.