Canine Lymphoma in Your Dog: A Pet Health Care Guide

Key Points

Canine lymphoma (also called lymphosarcoma) is a common cancer in dogs
It is a cancer of white blood cells called lymphocytes but can affect any part of the body
Clinical signs vary according to the body part affected
We do not know what causes it
Diagnosis requires a sample from the affected tissue and classifying it further (called “staging”) helps determine the best treatment course
While canine lymphoma is often aggressive when left untreated, it often responds quite well to treatment, adding months to years to the patient’s life

Understanding Lymphoma

Canine lymphoma (also called lymphosarcoma or LSA) is one of the main cancers of dogs, accounting for approximately seven percent to 24% of all canine cancers. While it typically affects middle-aged and older dogs, it can occur in any aged dog, as well as any breed. It is a cancer of lymphocytes, which are small white blood cells that play a role in the body’s immune response in the fight against germs and diseases.

Though we do not know what causes lymphoma, it occurs when there is a change within the lymphocyte that causes it to become destructive and capable of reproducing without limits, and even invading other tissues. Some factors that may contribute to this malignant change include genetic predisposition, viral infection, and exposure to herbicides or electromagnetic radiation.

Classification

While it can be quite alarming to learn your dog has been diagnosed with LSA, it often responds quite well to treatment. Learning as much information as possible about your dog’s specific type of lymphoma is crucial before treatment can be initiated.

While lymphocytes are a specific type of cell within the blood, LSA is not restricted to the blood. It may originate in the lymph nodes, spleen, liver, bone marrow, thymus, gastrointestinal tract, skin, liver, lungs, and virtually any place in the body. Learning what body parts are affected is the first step in classifying LSA. It most commonly affects multiple locations; this type is called multicentric LSA. When the bone marrow or peripheral blood is affected, it is called leukemia. Microscopic examination can further classify LSA as low, intermediate, or high grades.

Furthermore, there are two main types of lymphocytes found in the body: B cells and T cells. The classification of LSA as B-cell or T-cell sub-types is important because this distinction is valuable for the specialist to predict duration of remission and overall survival. Generally speaking, B-cell LSA carries a better prognosis than T-cell LSA; luckily, B-cell LSA is the more commonly diagnosed type.

Signs & Symptoms

Clinical features of canine lymphoma vary based on the area of the body involved. Seemingly painless, generalized swollen glands (which are actually lymph nodes) that can be seen or felt under the neck, near the shoulders, or behind the knees is a common finding by pet parent or veterinarian. Decreased appetite, lethargy, and weight loss are often noted, but other signs are very organ specific. For example, skin lymphoma will cause generalized skin lesions that may appear as a rash initially and later progress to bigger scaly, crusted, inflamed, and hairless lesions. Similarly, vomiting and diarrhea are seen when the gastrointestinal tract is affected. Elevated calcium may be found on routine blood work and pet parents may report increased thirst in such cases. When the cancer is found in the lungs, owners may notice shortness of breath. It is important to remember any part of the body may be affected so the range of clinical signs seen is extensive.

Diagnosis

Diagnosis of LSA is not a major challenge for dogs that are presented with generalized lymph node enlargement. Confirmatory diagnosis can easily be established by aspiration cytology or by biopsy of the tissue involved.

After a diagnosis is established, clinical staging is pursued to determine the extent of cancer involvement. The clinical staging evaluation includes blood work, urinalysis, chest radiographs (x-rays), and abdominal imaging (radiographs or ultrasound). Molecular staging can also be performed.

While this process may sound overwhelming, moving from a diagnosis to treatment in the canine world is very swift and efficient in comparison to human health care and oncology. We encourage pet parents to consult with their family veterinarian or local veterinary medical oncologist to determine the best treatment plan. With the proper veterinary health care team in place, you can go from diagnosis to initiating treatment within little more than one week.

Treatment & Aftercare

Numerous advances in veterinary oncology have been made over the last couple decades, improving survival times for canine lymphoma drastically. Systemic anticancer chemotherapy is the treatment of choice for canine lymphoma. Many different drugs have been utilized either singly or in combination for the treatment of lymphomas in dogs. Combination chemotherapy has been reported to result in response rates up to 96%, prolonged remission (215 to 250 days) and survival durations of approximately one year. Some of the different drugs used include: L-asparaginase, vincristine, cyclophosphamide, doxorubicin, and prednisone. While combination chemotherapy is currently the treatment of choice, bone marrow transplants are available at select facilities and future treatment may include immune therapy with vaccines.

Your veterinary medical oncologist will work with you to determine the best treatment plan that fits your ideal balance of quality of care and costs. During treatment, regular monitoring and checkups are required for evaluating the patient’s response. Plans remain flexible and are adjusted as necessary throughout treatment to best meet the goals of both the patient and the pet parent.

Prognosis

Overall, canine LSA is a very treatable condition. It is important to realize that the treatment goal is not for a cure, but instead for high-quality, disease-free time to be added to the patient’s life. Most pet parents are very happy with the clinical outcome and response to therapy. While combination therapy survival rates average around one year, approximately 20% of dogs survive more than two years with currently available treatments.

Did you know? Chemotherapy in dogs is very different than chemotherapy in people. This is because your veterinary medical oncologist will tailor a treatment plan utilizing lower drug doses over a longer period of time to minimize side effects. Most dogs seem to take LSA treatment in stride, experiencing no or minimal side effects

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