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S. Ettinger1
Canine Lymphoma
Sue Ettinger, DVM, DACVIM (Oncology)
Dr Sue Cancer Vet PLLC and Animal Specialty & Emergency Center Wappinger Falls, NY, USA Key Points
• Lymphoma is a common canine cancer and is a systemic disease that requires chemotherapy in almost all cases.
• The majority of dogs achieve a complete remission with chemotherapy (approximately 80%). Higher remission rates are typical with CHOP multi-agent chemotherapy protocols.
• Early accurate diagnostics and careful staging are keys to proper clinical decision-making.
• To determine the best protocol for a patient and owners, it is important to understand efficacy of the various protocols, the potential toxicities, and prognostic factors.
• Dogs treated with chemotherapy live significantly longer than untreated dogs, and chemotherapy is generally well-tolerated in most dogs. Only a minority develops significant toxicity.
• The diagnostic and treatment choices can be confusing and overwhelming. In this talk, we will take “My 3 P’s” approach – prognostic, practical and pertinent.
Biology of lymphoma
Lymphoma is a collection of cancers arising from the malignant transformation of lymphocytes. Even though lymphoma is clinically a diverse group of neoplasms, the common origin is the lymphorecticular cells. Lymphoma is one of the most common canine cancers, accounting for 7-24% of all canine tumors and 85% of hematopoietic tumors. Dogs of any age, gender, and breed can be affected with lymphoma. Affected dogs are typically middle aged to older dog.
Anatomic Classification
Multicentric (PLN) is the most common form, accounting for 80% of lymphomas. Most dogs are typically asymptomatic, and 20-40% are clinical (substage b) with anorexia, lethargy, fever, V/D, weight loss, melena.
Clinical Appearance
Historic findings: The most common complaint is generalized lymphadenomegaly. Owners commonly report that lymph node size is rapidly increasing – over days to 1 to 3 weeks. In the early stages, dogs appear healthy and are not showing clinical signs. When present, clinical signs tend to be nonspecific and include vomiting, diarrhea, melena, anorexia, fever, and weight loss (substage b).
Common examination findings: Lymphoma can
be indolent or aggressive, solitary or multicentric, or node-based or associated with any organ. Non-painful generalized lymphadenomegaly is most common physical exam finding. Multicentric lymphoma involving the peripheral lymph nodes is most common, accounting for 80% of patients.
Most dogs are “healthy” substage a. T-cell dogs tend to be sick (b). In dogs, multicentric LSA is generally the NHL (non-Hodgkin’s LSA) form. Hepatosplenomegaly is common. Diffuse pulmonary infiltration has been reported in 27-34% based on CXR but on BAL, lung involvement may be higher. The lack of generalized lymphadenomegaly does not eliminate the possibility of lymphoma, as some dogs will have internal involvement only (i.e. hepatosplenic form, GI). Another scenario that can lead to confusion is hypercalcemia, often without peripheral lymphadenomegaly so lymphoma is not suspected.
Preliminary Diagnosis
Cytology Confirmation of lymphoma starts with fine needle aspirate of an affected lymph node. Cytology
is minimally invasive, less expensive than biopsy, and typically provides rapid results, in 1 to 2 days. Cytology reveals monomorphic abnormal lymphocyte populations. Cytology does not provide complete classification, grading, or phenotype. Avoid reactive LN, such as the mandibular LN.
Diagnostic Work Up
The minimum tests required for treatment are cytological confirmation (lymph node or affected organ), CBC, chemistry panel and urinalysis. The next diagnostic
I encourage owners to submit is phenotyping to determine B vs T-cell subtype. Phenotyping is typically determined with immunocytochemistry from aspirates, immunohistochemistry from biopsy, or flow cytometry
or PARR from aspirates. If there is a peripheral lymphocytosis on CBC (stage V), flow cytometry can be submitted on a whole blood sample to determine phenotype. Phenotype is the best independent prognostic factor; prognosis is worse with T-cell than B-cell.
An Urban Experience

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