Canine lymphoma
Lymphoma is a relatively common cancer in dogs. It forms when a mutation occurs in the lymphocyte (a type of white blood cell). The job of the lymphocyte is to make up the lymph tissue in the body, especially in the external lymph nodes, spleen, liver, abdomen, chest, skin, and bone marrow. For this reason, it is considered a body wide (systemic) disease.
Currently, there is not a clear underlying cause for canine lymphoma. Most dogs diagnosed with lymphoma have multiple enlarged lymph nodes and generally feel well. However, some dogs show vague symptoms including decreased appetite, lethargy, and weight loss. More affected dogs (especially Boxers) can experience increased thirst, increased urination, anorexia, elevated calcium, weakness, and cough.
Workup
The workup for a dog with lymphoma depends on their current clinical signs. In most case the workup for lymphoma consists of bloodwork (complete blood count and chemistry panel), cytology/needle aspirate to obtain a tissue diagnosis, and flow cytometry to assess cell type and prognosis. Sometimes, additional tests are warranted and may include chest x-rays to assess for enlarged internal lymph nodes or lung involvement, abdominal ultrasound to assess for abdominal organ (especially intestinal tract) involvement, or a urinalysis if kidney disease is suspected.
Chemotherapy (general)
Systemic chemotherapy is the mainstay of treatment since lymphoma is a body-wide disease. In general, lymphoma is very sensitive to chemotherapy and will induce remission in up to 95% of patients when multi-agent protocols are utilized (see below).
Remission means that the lymph nodes are small, there’s no evidence of organ involvement, or clinical signs have resolved. While most forms of lymphoma are not curable, we are usually able to induce a durable remission and provide a good quality of life. Contrary to chemotherapy in human medicine, chemotherapy is usually very well tolerated in dogs. About 30% of patients develop self-limiting mild to moderate adverse events including decreased appetite or diarrhea. About 10% of patients have side effects that require them to return to the hospital for short-term supportive care. These cases are usually due to dehydration or infection from a low white blood cell count. Serious side effects are seen in 1-5% of patients.
Doxorubicin can cause damage to the heart muscle if given multiple times, although most dogs do not receive enough of this drug to be a concern.
Cyclophosphamide can cause irritation to the bladder wall in a small percentage of dogs. If this occurs, you will see changes in urination (blood in the urine, straining to urinate, and frequent urination).
Tanovea can cause skin ulceration and very rarely scarring of the lung tissue. It is not recommended for use in dogs with lung disease or West Highland White Terriers. In general, dogs will not become bald but may have thinner hair.
Most protocols require a tapering steroid regimen for the first month of treatment or the entire treatment. Side effects of steroids include: increased hunger, weight gain, increased urination and thirst, panting, muscle wasting, and a pot-bellied appearance.
Chemotherapy options and prognosis:
19 week CHOP protocol:
- Vincristine week 1, cyclophosphamide week 2, doxorubicin week 3, off week; repeated 5 times
- >90% response rate
- First remission duration: 8-10 months
- Median survival time: B cell- 12-14 year, T cell- 6-9 months
Single agent Doxorubicin:
- Every three weeks for 5 doses
- Response rate: 70-75%
- First remission duration: 6-8 months
Prednisone alone:
- Daily for the dog’s life with rechecks as needed for quality of life
- Most dogs will at least have a partial response
- Median survival time: around 2 months
Once patients are finished with their chemotherapy protocol, we recommend monthly rechecks to ensure your pet remains in remission. It is important to remember that most patients will come out of remission before 1 year and will require backup chemotherapy to reach the median survival time.
In addition, dogs with T cells (large cells) typically do not achieve as long of survival times.
CHEMOTHERAPY MONITORING AND SAFETY:
Monitoring: Most patients tolerate chemotherapy well, but gastrointestinal side effects and bone marrow suppression resulting in infection are possible. Please monitor for gastrointestinal upset (vomiting, diarrhea, poor appetite), which most often occurs 2-5 days after treatment and signs of infection (sudden lethargy, poor appetite, shivering), which most often occurs 7-10 days following treatment. If noted, please call us. Infection and significant gastrointestinal side effects are unexpected, but can be life-threatening if not treated.
Safety: Your Doctor will be excreting chemotherapy in urine and feces for the next 3 days so we recommend you take the following precautions. Please walk them to urinate and defecate in low traffic areas. Wear gloves when cleaning up any accidents and clean the area 3 times with dish soap and water using paper towels. Double bag all waste in plastic bags and throw in the garbage. Wash hands well. Children, women who are pregnant, and anyone trying to get pregnant should not handle waste during this time.