Canine lymphomas (CLs) are a diverse group of cancers, which can vary greatly in their behavior – from rapidly progressing to chronic, indolent diseases. CLs are among the most common cancers diagnosed in dogs (7-14% of all cancers diagnosed in dogs). CLs may affect any organ in the body, but most commonly originate in lymph nodes, before spreading to other organs such as the spleen, liver, and bone marrow.
What is lymphoma?
Lymphomas are cancers that are derived from white blood cells (lymphocytes), cells that are part of the immune system. Although lymphoma can affect any organ in the body, it most commonly arises in organs that function as part of the immune system - lymph nodes, spleen, and bone marrow. By far the most common type of CL is multicentric lymphoma, in which the cancer first becomes apparent in lymph nodes.
Other common CLs include lymphoma of the skin – cutaneous lymphoma, lymphoma of the stomach and/or intestines – alimentary or gastrointestinal lymphoma and lymphoma involving organs within the chest, such as lymph nodes or the thymus gland – mediastinal lymphoma.
What causes lymphoma?
As with most of the cancers in animals, unfortunately, the cause of CL is not known. Suppression of the immune system is a known risk factor for the development of lymphoma in humans. However, the link between immune suppression and lymphoma in dogs is not clearly established.
What would I notice if my dog would have lymphoma?
The most common initial symptom of multicentric lymphoma in dogs is firm, enlarged, non-painful lymph nodes. Such a lymph node will feel like a hard, rubbery lump under your dog’s skin. The most easily located lymph nodes on a dog’s body are the mandibular lymph nodes (under the jaw) and the popliteal lymph nodes (behind the knee). Other common symptoms include loss of appetite, lethargy, weight loss, swelling of the face or legs (edema), and occasionally increased thirst and urination.
Cutaneous lymphoma tends to appear first as dry, flaky, red, and itchy patches of skin anywhere on the body. It may be easily mistaken for an allergy, atopy or dermatitis (skin infection/inflammation). As the disease progresses, the skin becomes moist, ulcerated, very red, and thickened. Cutaneous lymphoma may also appear in the mouth, often affecting the gums, lips, and the roof of the mouth and may look similar to periodontal disease in its early stages.
Dogs with gastrointestinal lymphoma usually have symptoms such as vomiting, watery diarrhea, and weight loss. The diarrhea is often very dark in color and foulsmelling.
Dogs with mediastinal lymphoma typically have difficulty breathing. This may be due to the presence of a large mass within the chest or due to the accumulation of fluid within the chest (pleural effusion). Affected dogs may also show swelling of the face or front legs as well as increased thirst and urination.
What will the veterinarian do to diagnose lymphoma?
Biopsy is a gold standard to diagnose lymphoma – either fine needle aspiration biopsy (with a sample submitted for cytologic evaluation) or sampling of a piece entire lymph node or other piece of organ (with a sample submitted to pathohistology). Additional sophisticated tests are nowadays available (e.g., flow cytometry) to diagnose specific types of lymphomas which can considerably influence the prognosis and treatment outcome. In Animal Hospital Postojna, flow cytometry is included in our diagnostic work-up of a dog with suspected lymphoma. This test is performed in co-operation with University of Milan, Italy and with world expert in lymphoma prof. dr. Stefano Comazzi, Dipl. ECVCP.
In addition to biopsy, we recommend several staging tests for dogs with lymphoma. The purpose of the staging tests is to determine how far the lymphoma has spread throughout your dog’s body. In general, the more places the lymphoma has spread to, the poorer the dog’s prognosis. However, dogs with very advanced lymphoma can still be treated and experience cancer remission. Staging tests also help us assess whether your dog has any other conditions that may affect treatment decisions or overall prognosis. The staging tests we typically recommend include blood tests, a urinalysis, x-rays or CT of the chest, an abdominal ultrasound, and a bone marrow aspirate.
Can we treat a dog with lymphoma?
The most effective therapy for most types of canine lymphoma is chemotherapy. In some cases, surgery or radiation therapy may also be recommended. There are numerous chemotherapy treatment protocols for dogs with multicentric lymphoma. Most dogs with lymphoma experience remission (regression) of their cancer following treatment, and side effects are usually not severe. Remission may be partial meaning the overall cancer burden has been reduced by at least 50%, or it may be complete meaning the cancer has become undetectable to any readily available screening test.
Currently, the protocols that achieve the highest rates of remission and longest overall survival times involve combinations of drugs given over several weeks to months. The protocol we use as a “gold standard” for the treatment of canine multicentric lymphoma is 19-week protocol called modified CHOP (based on cyclophosphamide, doxorubicin, vincristine, and prednisone). In general, 70-90% of dogs with multicentric lymphoma treated with modified CHOP protocol experience complete or partial remission of their lymphoma, with most dogs experiencing complete remission. This protocol may not be appropriate for all dogs with lymphoma.
Different types of lymphoma may be treated with different chemotherapy drugs. For instance, the most effective drug for cutaneous lymphoma is thought to be lomustine (CCNU). We strive to provide a treatment plan that would best fit your dog's disease.
What can you expect if you decide to treat your dog with lymphoma at Animal Hospital Postojna?
Most chemotherapy drugs are given by intravenous (IV) injection, although a few are given by mouth as a tablet or capsule. Typically, an IV catheter will be placed in one of your dog’s veins to allow us to administer chemotherapy safely. A small patch of hair will be shaved over your dog’s leg where the catheter is placed. It usually takes 30-60 mins to get the IV chemotherapy.
Basic blood tests (CBC) are always performed prior to each treatment, mainly to assess the number of blood cells, which tipically are reduced after each chemotherapy and normally regain normal numbers before the next chemotherapy session is scheduled.
How will my dog feel after chemotherapy?
Most dogs tolerate chemotherapy well, much better than humans typically do. Although some dogs do get sick from chemotherapy, serious side effects are uncommon. In general, fewer than 5% of dogs treated for lymphoma using chemotherapy will experience side effects that need to be managed in a hospital setting. The most common side effects include loss of appetite, decreased activity level, and mild vomiting or diarrhea that persists for one or two days. If serious or unacceptable side effects occur, it is important that you inform us about this as soon as possible to evaluate your dog and provide supportive treatment if needed. In addition, we may recommend reducing the dose of chemotherapy the next time it is to be given. Unlike people, dogs usually do not lose their hair when treated with chemotherapy. The exceptions to this rule are poodles, Old English sheepdogs, and some terriers – these breeds may lose their hair while receiving chemotherapy. Hair growth should resume once chemotherapy is discontinued.
Is lymphoma curable?
Unfortunatelly, only in rare instances, dogs are cured of their lymphoma by chemotherapy, while most dogs will have a relapse of their cancer at some point. A second remission can be achieved in a large number of dogs, but it is usually of shorter duration than the first remission. This is because the lymphoma cells become more resistant to the effects of chemotherapy as time goes on. Eventually, most lymphomas develop resistance to all chemotherapy drugs, and dogs with lymphoma die or are euthanized when the cancer can no longer be controlled with chemotherapy.
Your dog’s prognosis is determined by what type of lymphoma he or she has, how spread the disease is (what stage), and what type of chemotherapy is used to treat the lymphoma. The median lenght of survival for dogs with multicentric lymphoma treated with modified CHOP 19-week protocol is between 9-13 months. (The term “median” implies that 50% of dogs will survive beyond this time point and 50% of treated dogs will die before this time point.) We will certainly discuss your dog’s prognosis in detail with you before any treatment decisions is started.
If you have noted any problems with your animal, please consult your veterinarian.
Article by Janoš Butinar
Based on: Purdue University, College of Veterinary Medicine