Lymphoma is one of the most common malignant, metastatic neoplasms that you will deal with in veterinary medicine. Forms of lymphoma are known to affect many different species, particularly cats, dogs, and horses. As far as cancer goes, this is one of the better neoplasms to have because it is one that we can actually treat and get good responses and reasonable survival times, especially in dogs.

Lymphoma is simply neoplastic proliferation of lymphocytes. Both T- and B-cell forms exist and the neoplasm can include cell morphology ranging from well-differentiated small lymphocytes to large, poorly-differentiated lymphoblast-like cells. Lymphoma may be restricted to local lymph nodes, it may be diffusely infiltrative, it may present as a lymphocytic exudate in a body cavity, and it may cause peripheral leukemia. Lymphoma can, in short, appear in many different forms with many different systemic and local effects and many different prognoses. In the human literature, there are many different "lymphomas", each of which has been studied in great detail and each of which merits entire textbooks all on its own. Lymphoma in veterinary medicine tends to be viewed as a singular entity since treatment does not differ much between the categories.

Perhaps the most important aspect of lymphoma to the practitioner is something we mentioned already - it is treatable. This does not mean that it is cureable. "Cure" is a word that is treacherous to use in cancer medicine under any circumstances. Human physicians talk of curing patients when there are no signs of lymphoma for over five years. Since most of our patients are geriatric when diagnosed with most neoplasms, a survival time of greater than five years is unlikely regardless of treatment outcome. Veterinarians speak of inducing remission, not of effecting a cure, and we measure our success in months, possibly in years. Dogs respond to treatment better than cats and they have fewer complications and side effects from chemotherapy.

Since the case before us is a cat, we will focus on feline lymphosarcoma although the dogs get their fair share of the disease, as well. Cats are unfortunate in that they can contract a disease that is highly associated with development of lymphoma - that is, of course, feline leukemia. The feline leukemia virus is susceptible to transformation in vivo into the feline sarcoma virus. If this transformation occurs, lymphoma is a likely outcome. It used to be thought that lymphomas in certain regions of the body (mediastinal masses, alimentary masses) were positively associated with feline sarcoma virus infection, but this has not been supported by recent research. What has been supported is that infection with feline leukemia increases the likelihood of infection with the feline sarcoma virus, which in turn causes lymphoma. Get your cat vaccinated and don't let him roam around at night.

That said, the typical presentation for a cat with lymphoma is a 2-6 year-old male with a history of going outdoors and/or fighting. This is due to the probable spread of feline leukemia virus through saliva and blood. It is also thought that immunosuppression (poor diet, stress, poor vaccination history) increases the chances of developing lymphoma when exposed to feline leukemia.

Lymphoma is categorized by anatomic location - mediastinal, alimentary, multicentric, cutaneous, extranodal, and primary CNS. Mediastinal and alimentary are the most common presentations, but the others are by no means rare. What follows is a brief outline of each presentation.

Mediastinal : Typical presentation is a young cat in respiratory distress. The neoplasm is often of T-cell origin and arises from the thymus. The anterior and posterior mediastinal lymph nodes are usually involved and the thorax is non-compressible due to the distension caused by the tumor. Respiratory distress is due to mechanical compression of the lungs and to pleural effusion, a common complication.

Alimentary : This form is usually seen in older cats and is typically of B-cell origin and arises from the gut-associated lymphoid tissue (GALT). Half of all feline alimentary lymphomas are found in the small intestine and about a quarter are found in the stomach. The mesenteric lymph nodes are often involved and a palpable mass or masses can be identified in the abdomen. The typical reason for presentation to the veterinarian is vomiting and diarrhea, often associated with chronic weight loss. Alimentary lymphomas can be confused with IBD when musocal biopsies are submitted for analysis.

Multicentric : This form can appear in young or old cats. It is usually spread throughout the body at the time of presentation and involves peripheral lymph nodes, the spleen and liver, and may infiltrate the bone marrow. Cats may present for a variety of reasons, depending on the organs affected by the tumor. Many people think of peripheral lymphadenopathy as a common presenting sign, but this is actually not the case. In cat, peripheral lymphadenopathy without organomegaly usually is indicative of a reactive or hyperplastic syndrome as opposed to lymphoma.

Cutaneous : Just as you would imagine, cutaneous lymphoma presents as lesions in the skin. It is usually a form of primary neoplasia, but it can also be secondary to multicentric involvement. If the epithelium is not invaded, the lymphoma is usually derived from B-cells. If the epithelium is invaded, T-cells are usually the culprits. Histochemical staining can help differentiate the two, but it is largely an academic pursuit. Cutaneous lymphoma can look like anything on the skin - erythema, alopecia, crusts, you name it.

Extranodal : This refers to lymphomas that arise outside of lymph nodes and infiltrate various tissues. This is not too different from the multicentric form but this classification is usually used for solitary masses outside of the nodes. The kidneys and retinas are frequent targets. In cases where the kidneys are involved, many show bilateral renomegaly with smooth contours. Half of the renal cases present in renal insufficiency.

Primary CNS : The typical presentation for cats with primary CNS lymphoma is paresis or seizures, depending on the location of the mass. Thorough neurologic examination, myelogram, CT, and MR are useful for localizing the lesion. CSF analysis may show lymphocytes and make the diagnosis. Otherwise, definitive diagnosis may have to wait until necropsy.

Any form : Any form of lymphoma can include bone marrow involvement and a concurrent anemia with leukemia. This profile is indicative of red cell precursor destruction by invasive white cell precursors in the bone marrow. While leukemia alone cannot be used to diagnose lymphoma, about half of all cases have some degree of leukemia, usually a lymphoid (lymphoblastic) form.

The diagnostic procedures for lymphoma, regardless of presentation and form, are approximately the same as for any other neoplasm. A baseline CBC and chemistry panel are taken with the addition of a platelet count. ELISA tests for feline leukemia and feline immunodeficiency virus should be performed as part of the serologic workup. A tissue diagnosis should be made if possible, and that can be done by fine needle aspirate (FNA) and/or core biopsy. Some say that lymphoma is one of three tumors that can be definitively diagnosed by fine needle aspirate (the other two are lipomas and mast cell tumors, but other people in the know say lipoma and mast cell FNAs are unreliable). A good FNA of a representative mass can certainly be diagnostic.

If the results are in doubt, however, histology is required. If the lesion involves the brain or spine, a CSF tap is a good idea. Lymphoma in the spinal canal will shed malignant cells into the CSF more than half the time and these can be read under the scope for a diagnosis.

As was suggested before, treatment of cats is often unrewarding. Chemotherapy, surgery, and radiation therapy have been used in the past with varying results. Chemotherapy is the mainstay of treatment, even in the presence of macroscopic disease. A complete response can be achieved about 60 - 70% of the time and the median survival time for these cats is about six months.