There are different types of canine lymphoma and therefore, it's important to learn more about the differences. Lymphoma is the most common type of cancer in dogs (10 to 25 percent of all diagnosed cancers are lymphoma). On the plus side, luckily lymphoma is one of the most successfully treated cancers. In fact, dogs with lymphoma tend to outlive dogs with heart, kidney or liver disease.
What is Canine Lymphoma?
The lymphatic system is involved in the immunity and responsible for fighting infections. The lymphocytes are an integral part of the lymphatic system. They normally travel around the body and protect the organism from invading agents. The lymphocytes are produced and stored in the lymph nodes which may be superficial (near the body surface) or profound (deep).
The term lymphoma indicates cancer of the lymphatic system. It is a blanket term that covers several types of cancers that stem from the lymphocytes. When lymphocytes travel around the body, if cancerous, they tend to spread the cancer throughout the entire body.
Since the lymphocytes are most concentrated in the lymph nodes, patients with lymphoma have increased lymph nodes. The condition can affect some or all of the lymph nodes in the body at the same time. In dogs with lymphoma, the superficial lymph nodes can be felt or even seen.
The Different Types of Canine Lymphoma
There are more than 30 different types of lymphoma. Determining the exact type is important because it provides important information about several factors such as the cancer’s progression rate, the length of the potential survival period and the clinical signs and symptoms.
Of the 30 different types of canine lymphoma, 4 are the most common:
- Multicentric lymphoma – 80 percent of the canine lymphomas are classified as multicentric. Multicentric lymphomas affect the lymph nodes and the primary physical sign are enlarged lymph nodes (sometimes up to 10 times). The enlarged lymph nodes are painless thus making early diagnosis difficult. As the condition progresses, dogs may exhibit lethargy, fever, weakness, dehydration and anorexia.
- Alimentary lymphoma – less than 10 percent are classified as alimentary. It affects the intestines and consequently diseased dogs suffer from vomiting, diarrhea, weight loss, anorexia, lethargy and severe abdominal pain.
- Mediastinal lymphoma – causes lymph node or thymus enlargement. Affected dogs have the following symptoms: difficult breathing, face swelling, increased thirst and increased urination frequency.
- Extranodal lymphoma – affects specific organs and the clinical manifestation depends on the affected organ. The most commonly affected organ is the skin. Dogs with cutaneous lymphoma have raised nodules or scaly lesions on the skin. Over time the lesions may progress to ulcers.
Within each lymphoma type there are 2 subtypes or phenotypes:
- B-cell lymphoma
It is estimated that 60 to 80 percent of lymphomas are categorized as B-cell. This type of cancer has a better response to currently available conventional treatments and therefore, has a higher rate of complete remission and longer remission. B-cell lymphoma is associated with increased survival time and is common in Cocker Spaniels, Doberman Pinschers and Golden Retrievers.
- T-cell lymphoma
It is estimated that 20 to 40 percent of lymphomas are categorized as T-cell. This type of cancer has a higher resistance to currently available treatments, a lower rate of complete remission and a shorter remission. T-cell lymphoma is associated with decreased survival time and is common in Boxers and Golden Retrievers. In a nutshell, patients with B-cell lymphoma have better prognosis than patients with T-cell lymphoma.
Did you know? In the cancer world, there's a saying to help differentiate B cell from T cell. That is B stands for better and T stands for tougher.
Canine Lymphoma Treatment Options
It should be noted that patients with lymphoma cannot be completely cured. Instead, the goal of the treatment is to prolong the dog’s life and increase the quality of that life for as long as possible and with minimal side-effects. This is called remission (the disease is not fully eliminated but it is not significantly and detectibly present).
Generally speaking, there are 3 treatment options:
- Steroid treatment – uses prednisolone that increases the average survival time to 1 to 3 months. Unfortunately, the steroid treatment is not always effective. What is more, steroid treatment makes subsequent chemotherapy less efficient.
- Chemotherapy – uses medications that either stop or hinder the cancerous cells’ growth and division.
- Clinical trials – there are many clinical trials for dogs with lymphoma but they are still in research phase and do not offer full resolution on their own.
All in all, the mainstay of lymphoma treatment is chemotherapy. Unfortunately, most owners are reluctant when it comes to chemotherapy because they do not want to poison their dogs. As scary as it may sound, chemotherapy is well-tolerated in most dogs and it significantly increases the survival period. It should be well-established that dogs do not get sick from the chemotherapy, they get sick from the lymphoma.
The currently used protocol is called CHOP and it includes administration of several agents such as cyclophosphamide, doxorubicin, vincristine and prednisone with or without l-asparginase.
Before receiving the chemotherapy, on each treatment day, the dog’s progress is evaluated through physical examination and blood tests. Once the dog is assessed, the chemotherapy dose is calculated and the drugs are administered under the skin (subcutaneously), into a vein (intravenously) via a catheter or through the mouth (orally).
The chemotherapy is usually given weekly for 4 weeks out of every 5 for 4.5-6 months. At the end, if the dog is in remission, the treatment is discontinued. If the patient relapses, the protocol is restarted.
As individuals, different dogs respond differently to the same treatment protocol. Therefore each dog needs individually tailored approach as well as close and careful monitoring.
The Side-effects of Chemotherapy
The agents used for chemotherapy damage both the cancer cells and the body’s normal but fast-dividing cells. Typically affected normal tissues include:
- The cells of the intestines – damage to these cells leads to variable appetite, changes in the stool consistency and occasional vomiting.
- The bone marrow cells (red blood cells and platelets but particularly white blood cells) – the damaged white blood cells lead to impaired immunity and increased susceptibility to infections.
- Hair follicles – hair loss is not as common in dogs as it is in humans. However, hair loss is a possibility in breeds with a continuously growing coat such as the Old English Sheepdog and the Poodle.
Additionally, steroids tend to increase the dog’s thirst and hunger, cyclophosphamide irritates the lining of the bladder thus causing cystitis-like symptoms and doxorubicin damages the heart muscle.
Prognosis For Patients with Lymphoma
Without treatment the average survival time for dogs with lymphoma varies based on the lymphoma’s type and extent ,but generally speaking it is between 4 to 6 weeks. With treatment, the average survival time is around 18 months.
About the Author
Dr. Ivana Crnec is a graduate of the University Sv. Kliment Ohridski’s Faculty of Veterinary Medicine in Bitola, Republic of Macedonia. She currently practices as a veterinarian in Bitola and is completing her postgraduate studies in the Pathology of Domestic Carnivores at the Faculty of Veterinary Medicine in Zagreb, Croatia.