Lymphoma is a common and biologically diverse cancer in dogs. Diagnosis of lymphoma is most commonly made based on clinical signs (enlargement of peripheral lymph nodes—see photo to the right) and fine needle aspiration (FNA) cytology. While clinical signs and FNA cytology alone are often sufficient to gain a diagnosis of lymphoma and therefore initiate treatment, several ancillary diagnostic tests are used in cases where the diagnosis is less clear cut or if further prognostication is desired by the pet owner and/or clinician. Such ancillary diagnostic tests may include a complete blood count, chemistry profile, bone marrow aspiration, thoracic radiographs, abdominal ultrasound, and biopsy. Advanced diagnostics that may be recommended included immunohistochemistry, PCR for antigen receptor rearrangement, and flow cytometry.
The most common form of lymphoma diagnosed in our canine patients is multicentric lymphoblastic lymphoma. This disease entity is clinically similar to non-Hodgkin’s lymphoma in people. Other, more rare forms, include mediastinal, cutaneous (epitheliotropic), gastrointestinal, and indolent lymphoma. Multicentric lymphoma is defined as peripheral lymph node involvement with or without involvement of the liver, spleen and/or bone marrow.
Prognosis for lymphoma varies considerably based on a number of factors. The most consistent and reliable of these factors include clinical stage and phenotype. Clinical stages are defined in table 1. Briefly, the higher clinical stage indicates a greater degree of systemic involvement and thus a more aggressive disease processes. The most common staging system is the WHO five stage scale (Table 1).
|I||One lymph node involved||Progression to higher stage often seen with local therapy(surgery) only|
|II||Multiple lymph nodes involved, but only on one side of diaphragm|
|III||Generalized lymphadenopathy||Patients with stage I-III disease have similar DFI and ST|
|IV||Stage III with splenic and/or liver involvement||Significance of differentiating stage IV from I-III is argued|
|V||Bone marrow involvement/leukemic, and non-lymphoid tissue involvment (brain, GI Tract, etc)||Patients with stage V disease survive significantly shorter than stage I-IV|
The mainstay of therapy for lymphoma is chemotherapy. It is important to realize when considering chemotherapy for pets, that animals tend to tolerate chemotherapy much better that their human counterparts. Please see Chemotherapy in Pets or click on the PDF logo to the right for more information on treatment protocols for Lymphoma.