What is lymphoma?

Lymphoma (also called Lymphosarcoma or Malignant Lymphoma) is one of the most common forms of cancer in dogs. There are between 1 to 3 cases per 10,000 of all dogs per year. It is a cancer of the white blood cells, similar to Non-Hodgkin's lymphoma in humans. Any breed of dog can be affected at any age, but middle aged dogs (between 6-9 years of age) are most commonly affected. Typically it presents as swellings in the lymph nodes, but can appear anywhere throughout the body, as white blood cells can access the whole body: specific areas of concern can include the skin, the internal organs and the bone marrow. This handout refers mainly to generalised lymphoma, the most common form.

Why has my dog developed lymphoma?

There are a few risk factors that have been identified, such as exposure to certain types of herbicide (2,4-D specifically), and a weak association with strong magnetic fields. With our increasing knowledge of molecular biology, we are beginning to identify some mutations and chromosomal abnormalities that are present in up to 40% of cases. However, most cases have no specific cause.

What is the outlook for my dog?

Generalised lymphoma is fatal if untreated, usually within a matter of weeks of diagnosis. However, lymphoma is a well understood disease, due to its relatively high frequency and similarity to human disease. This means that we have a good level of understanding of how the disease works, and how best to treat it. It is, in fact, one of the most responsive of all cancers to treat with chemotherapy. With the Gold Standard protocols, we can achieve a remission rate of over 90%. Around 50% of patients survive for over one year, and 25% survive for 2 years or more, with some of these effectively "cured" of their disease.

It is important to be aware of the difference between remission and cure. Remission is the term for reduction or disappearance of clinical signs, and this is the primary aim of chemotherapy for lymphoma. Cure is the removal of disease from the body, and is much harder to achieve. We do cure some of our patients with chemotherapy, but to try to cure more would result in increased occurrence and severity of adverse side effects. This is one of the areas where chemotherapy in humans differs from that in animals.

What happens next?

The first step in treatment is confirming diagnosis. This may seem an unnecessary process, given the distinctive nature of the signs in many cases. However, proper & full diagnosis can have a profound effect on the type of treatment and ongoing prognosis for your dog.

Diagnosis is based first of all on clinical signs. Typically in generalised lymphoma this is enlarged lymph nodes in an otherwise well dog, but lymphoma can cause many much more subtle or profound signs, depending on where in the body the disease is to be found. Some other clinical signs can include increased thirst and urination, difficulty breathing, or general lethargy, all with or without enlarged lymph nodes. Sometimes there are very few signs, and the disease can remain undiscovered until a late stage.

Biopsy of an enlarged lymph node or affected organ usually gives us a definitive diagnosis as to the type and grade of disease. This gives us more information about how the disease may respond and progress, as well as confirming the disease itself. This is a very important step given that treatment can be intense and expensive: we do not want to treat animals

who do not need treatment. It is also important to perform blood testing, to see how the rest of the body is functioning before treatment starts, and to check for any other signs of disease elsewhere. A sample of bone marrow is usually taken for analysis, to assess the egree of disease invasion into the blood manufacturing systems there. Other tests performed may also include chest X-rays and abdominal scanning with ultrasound.

When we have a complete picture of the disease, we can formulate the best approach to treatment.

Treatment

We treat most lymphoma best using chemotherapy. The aim of treatment is to cause maximum damage to the cancer while leaving the patient unharmed and well. This is achieved by using carefully worked out treatment protocols and close monitoring of the patient during the treatment process, to ensure that your pet suffers little or no side effects, and this goal is usually reached in 95% of cases. Side effects can include gastrointestinal upsets including loss of appetite, vomiting and diarrhoea; some loss of hair n non-moulting breeds such as poodles; and suppression of bone marrow function, leading to loss of protective white blood cells, which may be life-threatening. See attached handout

"Chemotherapy in Pets: Side-Effects" for more details.
Our Gold Standard protocol involves around one treatment per week for the first 9 weeks, then one treatment per fortnight for the following 16 weeks. Most of these treatments are injected, some are tablets. Blood tests are required throughout the protocol to monitor the response of the body to the treatment. The whole protocol takes around 6 months to complete. In most cases, rapid remission (disappearance of signs) is achieved and maintained (see above). Costs are around $250-300 per treatment, so the total is in the region of $4-5000 for the whole protocol. Clearly this protocol requires a high level of commitment from an owner, as frequent hospital visits are required and the cost is substantial.

Less intensive protocols are possible using a single cytotoxic drug less frequently, and can be reasonably successful with up to 80% response rates, and 50% survival at 9 months after diagnosis and treatment commencement.

Using cytotoxic drugs in our household pets carries a risk of exposing the owners to the same agents. While the risk associated with such exposure is small, and can be reduced further by following some simple steps, some owners may not wish to expose themselves or their families to such a risk. See the attached handout "Chemotherapy in Pets: Safety" for more details.

Palliative treatment is also possible using non-cytotoxic drugs, but remission is generally short (1-2 months).

Diet

There is evidence that diet can have an effect on lymphoma. Cancer cells use simple metabolic pathways to get their energy, and by moulding the diet we can reduce the food available to the cancer cells, whilst maintaining the body's nutrition. One food company have developed a specific food for this purpose (Hills n/d), and this can be a useful adjunct to treatment, as long as the patient themselves gets on well with the food.

Skin lymphoma

Epitheliotropic lymphoma (skin/cutaneous lymphoma, Mycosis Fungoides) is a specific form of localised lymphoma. It is a less aggressive disease than generalised lymphoma, but can be severe. It is less responsive to chemotherapy, but can be treated using a cytotoxic drug, with remission achieved in around 50% of cases. Biopsy is needed to confirm diagnosis.

Summary

Lymphoma is an aggressive and fatal disease if untreated. Treatment with chemotherapy is usually very effective, with minimal side effects and a very good chance of long, diseasefree remission in most cases. It is almost always possible to improve the quality of life of a dog with lymphoma, at least for a short while.

If you have any questions, please contact your local Vets4Pets practice.