Lymphoma is the most common cancer in dogs. It is usually encountered in middle-aged to older dogs and cats but it can occur at almost any age. Both males and females can be affected. The most common sites for the development of lymphoma are the lymph nodes and often many are affected simultaneously. Other common sites in dogs for the disease include the mediastinum (within the chest), the abdominal organs (liver, spleen, kidneys, intestines), the central nervous system, and the skin. In cats, lymphoma arises most frequently in the gastrointestinal tract but can also arise within the nasal passages in some patients.

Clinical Signs
Because this type of cancer can arise in a multitude of body systems, the clinical signs can be highly variable in both dogs and cats. Surprisingly up to 60% of dogs with this disease have no clinical signs at the time of diagnosis. This is particularly true when the cancer is limited to a patient’s external lymph nodes, as the disease is recognized by owners, groomers, or the general practicing veterinarian. When identified at this stage the only indicator of a problem may be the presence of large swollen lymph nodes in a patient’s neck, hind legs, groin, or armpits. In about 40% of dogs clinical signs are present at diagnosis and these can include lethargy, loss of appetite, fever, gastrointestinal upset, increased urination and/or drinking, or other more specific signs attributable to the site of cancer involvement (e.g. seizures for central nervous system invasion; coughing for lymphoma in the chest cavity). Fortunately most of these signs do resolve with treatment rather rapidly after initiation.

In cats clinical signs are more frequently identified at diagnosis because external lymph node enlargement is a much less frequent finding. Cats usually have clinical signs attributable to the organ that is involved: vomiting, diarrhea or weight loss for gastrointestinal lymphoma; renal failure for kidney lymphoma; trouble breathing or coughing for mediastinal lymphoma; nasal discharge or noise for nasal lymphoma; etc…). One form of lymphoma that is rarely found in cats is Hodgkin’s lymphoma in which large but usually asymptomatic swellings are found in the affected patient’s neck.

Lymphoma can be diagnosed in numerous ways. Most frequently a needle aspirate is performed to diagnose the disease. This involves the insertion of a needle into the affected organ and suctioning of cells into a syringe. The cells are then ejected onto a slide and evaluated by microscope. This simple technique is often diagnostic for the disease. In some instances slightly more invasive or advanced procedures are required to diagnose the disease. Such procedures may include a surgical biopsy, DNA analysis, or a technique called flow cytometry. When these techniques are used there is a high likelihood of confirming the disease if it is present. In very rare instances the disease may be missed on these procedures. Misdiagnosis is similarly uncommon.

Biological Behavior
It is critical to realize that for almost all forms of lymphoma, the disease is usually quite advanced at the time of diagnosis. This is because the disease arises from a cell called a lymphocyte. Lymphocytes are cells of the immune system and they have the ability to travel throughout a patient’s body. Malignant (cancerous) lymphocytes retain this ability to move through the lymphatic system and blood stream to various parts of the body. Therefore, long before there are enough cancer cells to be detected by the casual observer, this cancer has usually traveled to many organs in a patient’s body. In many instances the cancer can be identified in each of these organs by cytology or biopsy. In some instances the cancer may not be visible but is suspected to be present in many locations because of lymphoma’s typical behavior.

Local Treatment Options
Because of the generalized nature of lymphoma in most patients, lymphoma is usually not treated with local forms of treatment like surgery or radiation therapy. Occasionally, surgery may be used in conjunction with chemotherapy to excise particularly problematic lesions associated with lymphoma (e.g. tonsilar enlargement that is obstructing breathing). Radiation therapy can be used to treat some patients with lymphoma as well. This is particularly true for cats with nasal lymphoma or Hodgkin’s lymphoma. Both of these disease can be treated with radiation therapy and controlled for long periods without additional care.

Systemic Treatment Options
It is critical to realize that the vast majority of patients with lymphoma will not have long term control of their cancer without effective systemic therapy. In the absence of treatment most patients will die of lymphoma (or be euthanized because of complications of the disease) within a few weeks to a few months of recognition. This is because lymphoma is a very rapidly replicating form of cancer and can progress very quickly. The major systemic treatment options for lymphoma include the use of corticosteroids and/or chemotherapy drugs.

Simple medical approaches
Corticosteroids (e.g. prednisone, prednisilone, dexamethasone) can be beneficial for patients with lymphoma and represent the easiest, most inexpensive way to attempt to control the disease. These drugs are generally given orally and may control the disease for an additional 1-2 months beyond what would be expected without any therapy. Fortunately the side-effects of these medications are generally minimal but include an increase in urination and drinking, increased appetite, and occasional stomach upset.

Chemotherapy – General Concepts
Chemotherapy is a word that creates an instant emotional response in everyone. Chances are that you, or someone you know, has experienced chemotherapy for the treatment of cancer. The reality of chemotherapy for animals is generally different from that of human cancer patients. Most people are pleasantly surprised at how well their pets feel while undergoing chemotherapy. This is because the goals of veterinary oncology are to maintain quality of life both during and after chemotherapy. For this reason the doses of chemotherapy are typically lower than those used in human oncology and about 80% of pets have no side-effects following such treatments.

Chemotherapy – Possible Side-effects
Unfortunately chemotherapy can have a variable impact on a patient’s body. These drugs are toxic substances and some patients are more sensitive to them than others. In the 20% of patients that develop side-effects from chemotherapy, there can be gastrointestinal or immunosuppressive complications. Gastroinestinal effects can include vomiting, diarrhea or loss of appetite. In some instances (5%) these complications can be severe enough to warrant hospitalization for supportive care (e.g. intravenous fluids, antibiotics, anti-nausea drugs). Fortunately the majority of these problems resolve completely within a few days. In these instances future doses of chemotherapy are reduced to avoid such side-effects and maintain as good a quality of life as possible. In very rare instances chemotherapy patients can develop a severe bacterial infection called sepsis which can lead to death. Fortunately this is remarkably rare when appropriate monitoring and dosing are employed (<1% of patients). Chemotherapy– Specific protocols There are a multitude of chemotherapy protocols that are variably effective for the treatment of lymphoma in dogs and cats. Unfortunately there is no one protocol that is the best for every patient. Part of the discussion you have with your oncologist will attempt to determine which protocol may be best for your pet. Considerations important for making this decision include the effectiveness of each protocol, the cost of each protocol, the frequency of hospital visits needed, the potential side-effects of each protocol, and the age, systemic health and tolerance of the patient. The choice of approach can often be complicated because generally the more intensively the disease is treated, the better the outcome but the higher the expense and frequency of hospital visits.

-CHOP Chemotherapy
This is the most intensive protocol and the only one studied extensively in cats. It requires weekly visits to the hospital for one month with every other week visits for five months thereafter. During most visits a dose of chemotherapy is given intravenously. This protocol utilizes multiple different drugs given in alternating fashion. The costs can rise to $6000-7,000 for the six months/ one year of treatment depending on the size of your pet and concurrent health concerns and monitoring. CHOP provides a response (remission) for 75-85% of dogs and about 50% of cats. Such remission last for about for about 14 months on average in both species. It is critical to realize that this represents an average and that some patients have remission for much longer (even 4-5 years in some instances) while other patients have only short remissions (a few months). It can be difficult to exactly predict a patient’s duration of remission but your oncologist can inform you of some of the important prognostic factors if you wish.

(aka doxorubicin) chemotherapy Adriamycin is one of the drugs given in the CHOP protocol and is the most effective drug available for lymphoma when used alone, particularly in dogs. It is given once every three weeks at a cost of $600/dose for up to 6 doses. The drug provides a response in 60% of dogs and the duration averages roughly 8 months or so. As described above it is usually well tolerated although unique side-effects of this drug is cardiac damage in dogs and renal failure in cats. Fortunately these are rare for patients who are appropriately monitored during therapy. Dogs are monitored with periodic echocardiograms during treatment; cats are monitored with bloodwork to assess kidney function. In rare instances cardiac or renal damage can be unpredictable and life-threatening.

(aka CCNU) chemotherapy Lomustine (CCNU) is another drug that is effective for some patients with lymphoma. Roughly 40% of dogs respond to this drug when it is given orally once every three weeks. It is unknown how often cats with lymphoma respond to this medication. The duration of response can be highly variable but seems to average around 4-6 months in previously untreated patients that respond to it. It is less expensive than the other protocols, costing about $250-350/treatment. Up to 8 treatments with this drug may be given depending upon a patient’s response and the drug’s toxicity. A unique side-effect of lomustine is that it occasionally causes liver toxicity. Thus we monitor liver enzymes very closely during treatment with this drug. In rare instances liver damage can be unpredictable and life-threatening.

Experimental Options
Your oncologist can also talk with you about more advanced medical approaches that may be available in other parts of the country. For example, half-body radiation has been used effectively after chemotherapy to prolong remission duration in dogs and cats. Such therapy is available in San Diego. Bone marrow transplants can be given after high dose chemotherapy to try to cure canine lymphoma. In some instances this can be effective. Unfortunately, both of these forms of therapy require extensive travel, are very expensive (~$4000 for radiation therapy, >$10-20,000 for bone marrow transplantation), and have some less predictable side-effects. For these reasons most owners opt not to pursue such therapies but we are happy to refer your pet to another hospital if requested.

Outcome of Therapy
Unfortunately lymphoma is often an incurable disease in spite of all that can be done. Although the majority of patients respond to initial therapy they do eventually emerge from remission in most instances. Sometimes further chemotherapy can be of great benefit for these patients but, again, the benefits are temporary. When owners opt to pursue chemotherapy for lymphoma after being fully educated about the likely outcome they often express substantial pleasure with the prolonged period of survival and lack of side-effects that their pets experience. Nonetheless, pursuing chemotherapy for lymphoma is not for every owner or every pet. It is critical that you be appropriately informed before making such a big decision for your pet’s well-being. If you have any additional questions regarding treatment protocols, expectations, side-effects, or other aspects of such therapy, please do not hesitate to ask one of our doctors or technicians.