Diagnosis and Treatment of Canine Lymphoma

Lymphoma is a cancer of a specific white blood cell called the lymphocyte. Lymphocytes are the major cells found in lymph nodes. The lymph system is found in blood and tissues throughout the body; it is a network of vessels and nodes through which foreign proteins and disease organisms are circulated. Lymphocytes have several roles in the immune system, including the production of antibodies and other substances that fight infection and disease. With lymphoma the cancer cells invade and destroy normal tissues. The most common site for lymphoma is the lymph nodes, but lymphoma cells, like lymphocytes, can grow anywhere in the body. When lymphocytes become cancerous within a lymph node, the node swells and hardens. Malignant lymphocytes travel through the lymph vessels to nearby lymph nodes. Soon all the nodes are enlarged. As the disease progresses, internal organs such as the liver, spleen, and bone marrow become affected. Flu-like symptoms progress and ultimately result in the death of the patient. Lymphoma is one of the most common cancers in dogs. Often, the canine lymphoma patient comes to the veterinarian because one or more lumps have been found. A veterinarian can rapidly determine whether the peripheral lymph nodes (those near the skin surface) are enlarged and firm.

Diagnosis

A diagnosis is often confirmed by aspirating a lymph node. This is done by placing a small needle into an affected lymph node and removing cells for microscopic evaluation. This is a relatively quick, painless, inexpensive procedure. In 10% of cases, however, surgical removal (biopsy) of a lymph node is required for a diagnosis. If lymphoma is suspected in areas other than the lymph node (e. g. chest, intestines, or bone marrow), x-rays and/or ultrasound and aspiration of the suspected organ may be required to complete the diagnosis.

Treatment

In most cases, lymphoma exists throughout the body’s lymphatic system. Chemotherapy is the treatment of choice for almost every dog with lymphoma. Treating the dog’s entire body with chemotherapy is important for lymphoma because the cancer cells are in many places in the body at once. Surgery and radiation are occasionally options if a single, local tumor exists (e. g. in the nose), but usually are combined with chemotherapy. Most patients (especially dogs) are not feeling particularly sick at the time of diagnosis. It may be tempting to put off treatment until the pet seems more ill. However, waiting can drastically reduce the chance for long term survival; remission is more frequently achieved, and lasts longer, if the patient is treated while he/she still feels healthy. The goal of chemotherapy for animals with lymphoma is to induce a complete remission, by killing most of the cancer cells. The term “remission” means that all symptoms of the cancer have temporarily disappeared. Test results for animals with lymphoma who are in complete remission look like those of normal/healthy animals. They do not have any signs of cancer, and all masses or lumps will have disappeared. They eat, drink, and run just as they did before they developed cancer. Remission is achieved in 80-90% of dogs and typically lasts 6-9 months. The length of remission depends upon many factors including the primary site of the cancer, how sick an animal is at the start of treatment and the extent of disease.,Some of the cancer cells do survive in an animal in complete remission, but the numbers of these cells are too small to detect. Eventually, these few cells will grow and the cancer will become evident again. When this happens the animal is said to be “out of remission”. When lymphoma returns, remission may be re-established in most dogs by restarting the original chemotherapy protocol, or by changing to a new set of chemotherapy drugs. Eventually, the cancer cells will become resistant or insensitive to all drugs and the cancer will no longer respond to therapy.

Although chemotherapy does not cure dogs with lymphoma, in most cases it does extend the length and quality of life. Without treatment the life expectancy in dogs with lymphoma is 1-2 months.

With treatment, in dogs that feel well, about 80% – 90% of dogs with lymphoma attain a complete remission with an average survival of 12-14 months.

Dogs that are ill, have involvement of organs other than the lymph nodes (bone marrow, lungs, etc.), or do not respond to chemotherapy generally have shorter survival times. Keep in mind that these are average values. Each dog is an individual and will respond to treatment differently. The term “cure” refers to the permanent removal of all traces of tumor such that no further treatment is needed. In effect, it is a permanent state of remission. While this is a possibility, it is more constructive and realistic to focus on increasing quality of life. The specific drugs and schedule will be tailored to your dog’s particular condition. It will depend upon how the cancer is behaving, how sick an animal is at the start of treatment, and any abnormalities in organ function (especially important are changes in liver and kidney function).

The most effective chemotherapy protocol is a multi-agent chemotherapy; several different drugs (vincristine, Cytoxan and Adriamycin) are alternated in order to reduce the chance that the tumor cells will become resistant and to reduce the risk of side effects. This protocol involves 16 weekly chemotherapy treatments; there is a week off after every 4th treatment, so treatments are administered over a total of 19 weeks. Other protocols include chemotherapy given once every 2 or 3 weeks (either oral or IV), although remission rates and average survival times may be decreased.

Toxicities can occur (20-30% risk) with chemotherapy but are generally mild. Most dogs will tolerate chemotherapy well and have minimal side effects. Veterinary chemotherapy is designed to extend a pet’s life as long as possible while maintaining a good quality of life. As a result, the undesirable side-effects normally associated with human chemotherapy are both less common and less severe in animals undergoing chemotherapy.

Side Effects

The most common side-effect is bone marrow suppression, but nausea and anorexia are also occasionally noted. In less than 5% of patients, this can lead to life-threatening infections which require hospitalization. While whiskers are commonly lost, substantial hair loss is not experienced by animals undergoing chemotherapy for cancer. There are some notable exceptions, such as poodles, terriers, schnauzers, Old English Sheepdogs, Lhasa Apsos, and Shih Tzus.

Serious side effects are only seen in about 5% of the patients treated. These can include nausea, vomiting, loss of appetite, diarrhea, extreme tiredness, or infection. Adriamycin can cause damage to the heart muscle if given multiple times, though most dogs do not receive enough of this drug to be a concern. Cytoxan can cause irritation to the bladder wall in a small percentage of dogs. If this occurs, you will see changes in urination (blood in the urine, straining to urinate, and frequent urination).

Unfortunately, the only way to know whether an animal is going to have a drug reaction is to administer the drug. Some animals never get sick during chemotherapy, others can be very sensitive to the drugs. If your pet has a serious reaction, the drugs or doses your pet receives will be adjusted with the goal of maintaining a good quality of life.

As an owner, you can help your pet with lymphoma by watching him or her closely after each treatment. Chemotherapy may suppress your pet’s white blood cell production and make him or her more susceptible to infections. These infections generally arise from bacteria that normally live in the intestinal tract, respiratory tract, urinary tract, and on the skin (not from the environment). Signs of an infection may include loss of appetite, vomiting, diarrhea, decreased activity, or depression. Call your veterinarian immediately if your pet appears ill while receiving chemotherapy. These signs are usually only brief reactions to the drugs, but prompt treatment can often prevent more serious side effects from developing.

A Choice

The most important aspect of cancer therapy is that you feel as comfortable as possible with your decision. There are no right or wrong answers, and each situation is different. What is right for one dog and their owner may be unacceptable for another family. If chemotherapy is not an option, either financially, logistically, or philosophically, you may consider treatment with prednisone. This can significantly improve quality of life, is inexpensive, has few significant side effects, and is an oral medication. Weekly rechecks are not necessary but monthly visits to your regular veterinarian are recommended.

If you have any questions or need help making the best decision for you and your dog, please let someone know.

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modified from Ethos Veterinary Health