Lymphoma in Dogs

by Dr. Audrey Harvey, BVSc (Hons)

Before we can understand what lymphoma in dogs is and how it affects them, we need to learn about the lymphatic system. This system is involved in protecting a dog's body from disease. It consists of a number of lymphatic vessels that carry a fluid called lymph around the body. This fluid is responsible for bringing bacteria and other unfamiliar proteins to the lymph nodes where they are dealt with by cells of the immune system.

The main cell type involved in the lymphatic system is the lymphocyte. They have several functions, including producing antibodies and destroying materials that are foreign to the body, such as infective organisms. When they become cancerous, the lymph nodes become hard and swollen. Malignant cells are carried through the lymphatic system to other lymph nodes elsewhere in the body. These cells can also move into the dog's bloodstream from where they spread even further. Ultimately, this cancer affects a dog's bone marrow and destroys their immune system, leading to anemia and increased susceptibility to infection.

Lymphoma Affects Dog Bone MarrowThere is no specific cause of lymphoma in dogs. However, it appears to occur more in Boxers, German Shepherds, Scottish Terriers, Poodles and Golden Retrievers. This suggests there may be an as-yet undiscovered genetic predisposition to the disease.

Symptoms of Lymphoma in Dogs

This is a disease of middle age in the dog, and up to 25% of canine cancers turn out to be lymphoma. Often, the first indication that a dog is suffering from this type of cancer is when their owner discovers they have an enlarged lymph node. When their veterinarian examines them, they may find that other lymph nodes under the neck, in the armpits and in the groin are also enlarged. Other than this, most dogs with lymphoma don't appear sick, and act quite normal. However, some may show signs of gastrointestinal disease including vomiting, diarrhea and weight loss.

Diagnosis of Lymphoma in Dogs

Your veterinarian can take a small sample of the enlarged node with a fine needle. This is known as a fine needle aspirate biopsy. It doesn't hurt your dog, and the sample can either be examined in the clinic or sent off to a laboratory for analysis.

If the diagnosis is confirmed, then it's time for some further blood tests to see how far the cancer has spread. The basic tests needed are a complete blood count, blood biochemistry and urine tests. The blood count may be completely normal, or it may show changes in the number of lymphocytes or red blood cells. Blood chemistry is important to check how well the internal organs are functioning. If there are any abnormalities, such as increased liver enzymes, then it suggests that cancerous cells have already spread from the lymph nodes to other parts of the body.

Veterinarians use a classification system to indicate the extent of the disease.

Stage 1 – there is just one lymph node involved, and there is no sign of any spread of the cancer.

Stage 2 – Two or more nodes are affected, both of which are either in front of the diaphragm, or behind it.

Stage 3 – Like stage 2, this stage involves two or more lymph nodes, but they are on different sides of the diaphragm.

Stage 4 – Any lymph nodes are involved, but there is spread to the liver or spleen.

Stage 5 – Other tissues such as the kidney, the eye or the bone marrow are affected by lymphoma.

Lymphoma in dogs can also be graded, depending on the degree of malignancy seen in the lymphocytes.

The higher stages and grades are usually associated with a more severe form of the disease, and they may not respond to treatment as well as the lower stages.

Treatment of Lymphoma in Dogs

Treating Lymphoma in DogsIf a dog just has one lymph node affected, it can be removed and the area treated with radiation. However, with most cases of lymphoma in dogs, chemotherapy is the mainstay of treatment.

There are many protocols used to treat lymphoma, but no matter which one is used, more than 80% of dogs will go into remission. This means that they have no more symptoms of cancer, and they are essentially well. However, they will relapse, and the symptoms of cancer will return at some stage. The goal of treatment is not to cure the disease, but to keep your dog healthy and enjoying life for as long as possible.

Most oncologists, or cancer specialists, treat lymphoma with a combination of drugs given according to a specific schedule. These schedules usually include a drug called Doxorubicin, because it tends to result in a longer period of remission. Doxorubicin is given in conjunction with Vincristine, Prednisone and Cyclophosphamide. Most cases of lymphoma respond very well to this, and the patient goes into remission.

There are side effects of the chemotherapy, but unlike people, these don't usually include hair loss. The drugs used to treat lymphoma kill rapidly dividing cells, so they can also affect the bone marrow, and the lining of the gastrointestinal tract. Side effects include a low white cell count which increases the risk of infection, and vomiting and diarrhea. Doxorubicin specifically damages the heart, and needs to be used with extreme care. Many oncologists recommend regular ultrasound examinations of the heart to make sure it isn't affected.

When the lymphoma returns, it is possible to treat with another course of chemotherapy, known as a rescue protocol. If a dog has been off chemotherapy for a few months before relapse occurs, then the same combination of drugs can be used. However, in general, the drugs used for a rescue protocol aren't those used in the first line of treatment for lymphoma. Lomustine, Actinomycin D and Asparginase can be used to treat relapses.

The success of rescue protocols varies. If a dog has already had a large number of drugs to treat lymphoma, or if they relapse while they are still undergoing the initial course of chemotherapy, the outcome isn't good.

There are some facilities in the United States where bone marrow transplants are available to dogs. The ideal candidate is a dog that is in remission, and don't have any other medical conditions. Cancer free cells are collected from their bloodstream, then their bone marrow is completely destroyed by radiation. The harvested cells are reintroduced to their body, and repopulate the immune system. This offers a cure in up to 30% of dogs with lymphoma and complications are extremely rare. The only real side effect is gastrointestinal upset associated with the radiation treatment.

Some dogs have multiple chemotherapy rescue protocols, and respond to each one. At some point, however, their lymphoma becomes resistant to treatment and no more remissions are possible.

Prognosis

If a dog is diagnosed with lymphoma and has no treatment at all, their average life expectancy is only about 2 months.

There are other indicators that treatment isn't likely to have a good result. High blood calcium levels are usually associated with a tumor mass in the chest, and have a short survival time, even with treatment. These dogs usually live less than 5 months. Similarly, dogs that are actually unwell when they are diagnosed survive for around 6 months.

However, with appropriate treatment, your dog's life can be extended by one year or more. This may not sound like much but to a dog, it is almost 10% of their expected lifespan.

There is no cure for lymphoma in dogs. Treatment will give you extra time with your dog, and the opportunity to come to terms with the eventual loss of your beloved companion.

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