Lymphoma in Dogs: Signs and Treatment Options
Lymphoma in dogs is a common cancer, accounting for approximately 7-14 percent of all canine cancers according to the Purdue University College of Veterinary Medicine. This type of cancer can present in multiple ways.
What Is Lymphoma?
Lymphoma is a cancer of the lymphatic system. The lymphatic system includes the lymph nodes, spleen, thymus gland, lymph vessels, and bone marrow. The main functions of the lymphatic system are to aid the immune system and move fluid through the body.
In dogs, lymphoma typically begins in the lymph nodes, but it can arise from lymphoid tissues anywhere in the body. Lymphoma is sometimes seen in the skin, eyes, central nervous system, and lungs.
When a dog develops lymphoma, they develop abnormal growth and replication of a specific type of white blood cell called a lymphocyte. This results in changes to the immune system’s ability to fight infection, changes to the movement of fluid throughout the body, and the development of metastatic tumors throughout the body.
In most cases, dogs with lymphoma will develop flu-like symptoms and eventually pass away from their cancer.
Causes of Lymphoma in Dogs
Lymphoma most often occurs in middle-aged to older dogs, but it can be seen in dogs of any age. The veterinary community is not currently certain as to what causes lymphoma in dogs. Because specific breeds are more susceptible than others, genetics are suspected to play a role.
Breeds that are more likely to develop lymphoma include:
- Golden Retrievers
- Scottish Terriers
- Basset Hounds
- Cocker Spaniels
- German Shepherds
While these breeds have an increased risk, any dog can develop lymphoma. Additional links have been reported between lymphoma and specific herbicides, regular exposure to radiation, living in an industrial area, exposure to hazardous wastes, and secondhand smoke.
Types of Lymphoma in Dogs
The “type” of lymphoma in dogs refers to various subcategories of lymphoma: B-cell lymphoma vs. T-cell lymphoma, high-grade lymphoma vs. low-grade lymphoma, or lymphomas named for their location within the body. The symptoms of lymphoma in dogs depend on which part of the body is affected by lymphoma.
B-Cell vs. T-Cell Lymphoma
The most basic division of lymphoma type is B-cell vs. T-cell. Lymphocytes are either B-cells (the type of white blood cell that produces antibodies against pathogens) or T-cells (which help signal other cells of the immune system and kill abnormal cells in the body).
B-cell lymphoma is more common and has a longer survival time than T-cell lymphoma in dogs.
High-Grade Lymphoma vs. Low-Grade Lymphoma
Lymphoma can be graded as high-grade (lymphoblastic) or low-grade (lymphocytic) based on the appearance of the cells. High-grade is more common and has a rapid onset and progression. Low-grade is more chronic and affects the dog more slowly.
Anatomically, the most common form of lymphoma is called multicentric lymphoma. Multicentric lymphoma in dogs presents with swelling of the lymph nodes. As the pet parent, you may notice these swollen lymph nodes under the jaw or in the neck, in front of the shoulders, the armpits, groin, or behind the knees. At the time of diagnosis, lymph node swelling is usually the only sign. However, some dogs will also experience weight loss, lethargy, vomiting, diarrhea, and excessive drinking.
In around 5-7 percent of cases, the dog has alimentary lymphoma. This is lymphoma originating in the gastrointestinal tract, most often the intestines. Clinical signs of this form of lymphoma include vomiting, diarrhea, appetite changes, and weight loss.
Mediastinal lymphoma is a rare form of lymphoma. The mediastinum is the area between the lungs. This area includes the heart, large blood vessels, trachea, esophagus, thymus, and some lymph nodes. When cancer develops in this area, the tumor usually takes up space in the chest cavity, pressing on other structures in the chest. The pet parent may notice coughing, shortness of breath, and exercise intolerance.
Extranodal lymphoma is a catch-all term for lymphomas that develop elsewhere in the body. Examples can include lymphoma of the central nervous system (CNS lymphoma), lymphoma that develops in the skin (cutaneous lymphoma), and lymphoma that develops in the lungs (pulmonary lymphoma).
Signs will differ based on where the lymphoma is. For example, dogs with CNS lymphoma may have seizures, abnormal mentation, circling, abnormal eye movements, and other neurologic irregularities. Cutaneous lymphoma in dogs may cause non-healing ulcers, papules, or red lesions on the skin.
Stages of Lymphoma in Dogs
Staging of lymphoma is based on the location of disease and how much it has spread throughout the body. Stages III through V are more common in dogs.
Stage I: Cancer is present in a single lymph node.
Stage II: Cancer is present in lymph nodes on only one side of the diaphragm (front of body or rear of body).
Stage III: Cancer is present in lymph nodes on both sides of the diaphragm.
Stage IV: Cancer is present in the liver or spleen.
Stage V: Cancer involves bone marrow, nervous system, or other unusual location.
Each of the stages of lymphoma in dogs is further subdivided into substage A and substage B. Substage A means the pet feels well, while substage B means the pet is feeling ill. Pets who are feeling well have a better prognosis than pets who act sick.
Diagnosing Lymphoma in Dogs
In most cases, your veterinarian will be able to diagnose lymphoma with a physical examination and cytology of an enlarged lymph node. To collect a cytology sample, they will stick a needle into the lymph node. This procedure is well-tolerated by most dogs without sedation. The veterinarian may read the sample in-house or may send the slides to a reference lab.
If the cytology is not conclusive or an aspirate cannot be collected based on the location of the tumor, the veterinarian will collect a biopsy (surgical sample), which will be interpreted by a reference laboratory.
Determining if your dog has B-cell or T-cell lymphoma requires sending microscopic slides and fluid from the lymph node to a reference laboratory. At the reference lab, they’ll perform a test called flow cytometry or immunophenotyping to determine if the cancer is B-cell or T-cell. This information is important for determining your dog’s prognosis.
Imaging will be recommended to determine spread of the disease. This commonly involves X-rays (radiographs) of the chest and abdomen, as well as abdominal ultrasonography. In cases where the cancer originates elsewhere in the body, like the nervous system, other imaging modalities like magnetic resonance imaging (MRI) or computed tomography (CT) scans will be recommended. Your dog may need to be sedated for radiographs or ultrasound, and they will definitely be sedated for MRI or CT. In some cases, a bone marrow aspirate may be recommended to determine if cancer is affecting the bone marrow. Your dog will be anesthetized for this. The veterinarian will also want to perform blood work and urinalysis for overall health screening.
While the initial diagnosis and simple staging may be performed by your private veterinarian, they usually refer you to a veterinary oncologist for additional diagnostics and treatment. Most private practices do not have a CT or MRI scan and do not perform chemotherapy treatments.
Treating Lymphoma in Dogs
Treatment for lymphoma in dogs can vary, depending on the stage, but chemotherapy is the mainstay of treatment for most cases.
While there are various protocols, combination chemotherapies (more than one drug) have better remission rates and duration of remission than single-agent chemotherapy. These protocols involve frequent visits to the oncologist for a predetermined number of chemotherapy injections.
Common chemotherapy agents used in the initial round of chemotherapy include:
The oncologist will want to check blood panels prior to each treatment to ensure the chemotherapy is being tolerated well.
Low grade lymphoma may be treated with oral chemotherapy, such as chlorambucil and prednisone.
While this can be overwhelming for you as the pet parent, rest assured that chemotherapy in dogs is aimed to preserve quality of life. Dogs tend to tolerate chemotherapy better than humans, and if your dog is having side effects, your veterinarian will alter the protocol or offer additional medications to ensure they’re still feeling well.
Side effects that you should report to your veterinarian include vomiting, diarrhea, decreased appetite, and acting ill, but dogs do not usually lose much fur. Chemotherapy is easier to go through with your pet if you know what to expect.
If you choose not to pursue chemotherapy, prednisone may be offered as palliative care. While this will not significantly improve the length of your dog’s life, it may help them to feel better.
Rarely are surgery or radiation therapy recommended for localized lymphoma. Radiation alone will not treat most cases of lymphoma, so chemotherapy will typically be recommended in addition to the localized therapy.
Eventually, the dog will not respond to chemotherapy and treatment will focus on palliative care. End stage lymphoma in dogs often causes loss of appetite, vomiting, and diarrhea. Most dogs with lymphoma will be euthanized once the veterinarian and pet parent feel the pet no longer has a good quality of life.
Cost to Treat Lymphoma in Dogs
Treating lymphoma can be expensive. You will have multiple options laid out before you by the oncologist, and there is no shame in choosing a more affordable palliative treatment over one that prolongs life. Your focus should be ensuring that your pet is comfortable.
For initial diagnosis and complete staging alone, you can expect to pay at least $500. If your dog will need a CT or MRI, this will increase the cost to over $1,000. If you elect for prednisone alone, treatment may be $20 to $30 per month. This is an affordable option for many pet parents. While prednisone may help your dog feel comfortable, the average lifespan with no treatment or prednisone alone is four to six weeks.
If you pursue chemotherapy, you can expect the cost to differ depending on what protocol you elect. The price is likely to be over $5,000 and can often exceed $10,000. Most dogs who receive chemotherapy will have a remission that lasts eight to nine months, and their survival can be a year or more. Almost all dogs will relapse. Around half of dogs can get a second shorter remission that lasts two to four months. The chemotherapy protocol the second time around is often different from the first round of chemotherapy.
Prognosis for Dogs with Lymphoma
Dogs who are in stages I, II, and III tend to have longer survival times than dogs in stages IV or V. Dogs with low-grade lymphoma have longer survival times than dogs with high-grade lymphoma, and dogs with B-cell lymphoma have longer survival times than dogs with T-cell lymphoma.
Dogs with T-cell lymphoma have a prognosis closer to six months, while dogs with B-cell lymphoma have a prognosis closer to one year if treated with chemotherapy. Dogs who have mediastinal lymphoma or lymphoma in the central nervous system have short survival times.
Note: All dogs are individuals, and prices vary by location. While survival times and costs are provided, your pet could live shorter or longer, and the amount you spend on treatment may be significantly different than the estimates we’ve provided.
How to Prevent Lymphoma in Dogs
It can be very hard on you as the pet parent to reckon with your dog’s lymphoma diagnosis, and many pet parents want to know why they’re facing this diagnosis. Was it something they did?
There is currently no known way to prevent lymphoma in dogs, meaning you should not blame yourself for your dog’s cancer. Work with your private veterinarian and your veterinary oncologist to determine what course of action is best for your pet and your family. While this diagnosis is hard, treatment is often rewarding and usually improves your pet’s quality of life, allowing you to spend more quality time together.