Lymphoma accounts for approximately 7-24% of all canine neoplasms and up to 83% of hematopoietic malignancies in dogs. Multicentric lymphoma represents roughly 80% of cases, making generalized peripheral lymphadenopathy the most common presentation. Use the Oncology Specialist for case-specific protocol discussions and the Bloodwork OCR for interpreting staging bloodwork.
Canine lymphoma is classified by anatomic location into four major forms. Multicentric lymphoma is by far the most common (approximately 80%), presenting as painless, generalized peripheral lymphadenopathy. Dogs are often otherwise well in early stages, which can delay owner recognition.
Alimentary (gastrointestinal) lymphoma accounts for 5-7% of cases, presenting with vomiting, diarrhea, weight loss, and malabsorption. Mediastinal lymphoma (approximately 5%) involves the cranial mediastinal lymph nodes and/or thymus, often causing dyspnea and pleural effusion. Extranodal lymphoma can affect virtually any organ, including the skin (cutaneous lymphoma), CNS, eyes, kidneys, and nasal cavity.
The World Health Organization staging system for canine lymphoma guides treatment decisions and prognosis. Understanding substage classification is particularly important, as substage b (clinical illness) carries a significantly worse prognosis than substage a (clinically well).
| Stage | Description | Clinical Notes |
|---|---|---|
| I | Single lymph node or single extranodal site | Rare presentation; consider localized treatment |
| II | Multiple lymph nodes in one region | Regional involvement only |
| III | Generalized lymphadenopathy | Most common presentation at diagnosis |
| IV | Liver and/or spleen involvement | Hepatosplenomegaly on imaging |
| V | Blood, bone marrow, or extranodal organ involvement | Worst prognosis; may include CNS involvement |
Each stage is further divided into substage a (no systemic signs) or substage b (systemic illness including anorexia, weight loss, fever, or lethargy). Dogs presenting substage b have median survival times approximately 50% shorter than substage a.
Immunophenotype is one of the most important prognostic factors in canine lymphoma. Determination via flow cytometry, immunohistochemistry, or PARR (PCR for antigen receptor rearrangement) should be pursued whenever possible.
B-cell lymphoma (approximately 60-70% of cases) generally carries a better prognosis, with median survival times of 12-14 months with CHOP-based protocols and overall response rates exceeding 85%. T-cell lymphoma (approximately 30-40%) is associated with shorter remission durations and median survival times of 6-9 months. T-cell disease is more commonly associated with hypercalcemia, mediastinal involvement, and cutaneous forms.
Golden Retrievers have a higher prevalence of B-cell lymphoma, while Boxer dogs are predisposed to T-cell lymphoma. Breed predisposition should inform, but not replace, definitive immunophenotyping.
The diagnostic approach to suspected lymphoma proceeds in a stepwise fashion. Fine-needle aspiration (FNA) of enlarged lymph nodes is the initial step and is diagnostic in the majority of cases, revealing a monomorphic population of intermediate to large lymphocytes. Excisional biopsy provides architectural information and is necessary for definitive grading.
The complete staging workup includes: CBC with differential (evaluate for anemia, thrombocytopenia, circulating neoplastic cells), serum chemistry panel (calcium, liver enzymes, renal values), urinalysis, thoracic radiographs (3 views), abdominal ultrasound with liver and spleen aspirates, bone marrow aspirate (if leukemic or cytopenic), and immunophenotyping via flow cytometry or PARR.
Warning: Hypercalcemia occurs in 10-40% of canine lymphoma cases (especially T-cell and mediastinal forms) and can cause acute renal failure. Always check ionized calcium at diagnosis. Aggressive IV fluid therapy with 0.9% NaCl is indicated for hypercalcemic patients prior to initiating chemotherapy.
The University of Wisconsin-Madison CHOP protocol (UW-25) remains the gold standard for multicentric lymphoma treatment. The protocol spans 25 weeks and uses four drugs in rotation:
| Drug | Dose | Route | Key Toxicities |
|---|---|---|---|
| Vincristine | 0.7 mg/m² | IV (strict perivascular) | Perivascular slough, mild GI, peripheral neuropathy |
| Cyclophosphamide | 250 mg/m² | IV or PO | Sterile hemorrhagic cystitis, myelosuppression |
| Doxorubicin | 30 mg/m² (>10 kg) or 1 mg/kg (<10 kg) | IV (slow, strict perivascular) | Cumulative cardiotoxicity, severe GI, myelosuppression |
| Prednisone | 2 mg/kg PO daily (weeks 1-4), then taper | PO | PU/PD, polyphagia, GI ulceration, iatrogenic Cushing's |
Overall response rates with CHOP exceed 85%, with complete response rates of 65-75%. Median first remission duration is approximately 6-8 months, and median survival is 12-14 months for B-cell lymphoma.
Warning: Doxorubicin is a potent vesicant. Extravasation causes severe tissue necrosis. Always confirm IV catheter placement with a saline flush before administration. Cumulative doses exceeding 180-240 mg/m² increase the risk of irreversible dilated cardiomyopathy. Baseline echocardiography is recommended.
Most dogs eventually relapse after first-line CHOP. Rescue protocols include CCNU (lomustine) at 70-90 mg/m² PO every 3 weeks, which achieves response rates of 30-40% with median response duration of 2-3 months. Other rescue agents include mitoxantrone, L-asparaginase (if not used in induction), mechlorethamine, and rabacfosadine (Tanovea-CA1).
Reinduction with the original CHOP protocol can be attempted if first remission exceeded 6 months, with expected second remission durations approximately half the first. Overall, second-line therapy provides incrementally shorter remissions.
Honest, compassionate prognosis communication is essential. Key points to discuss with owners include: lymphoma is typically not curable but is highly treatable; chemotherapy in dogs is generally well-tolerated with a less than 5% rate of hospitalization for side effects; quality of life is usually excellent during remission; without treatment, median survival is 4-6 weeks; with prednisone alone, 1-2 months; with CHOP, 12-14 months for B-cell disease.
Financial counseling is also important, as a full CHOP protocol typically costs $5,000-$10,000 depending on geographic location and patient size. Discuss alternatives such as single-agent protocols (prednisone alone, CCNU alone) for clients with financial constraints.
- Multicentric lymphoma (80% of cases) presents as painless generalized lymphadenopathy.
- Immunophenotype is critical: B-cell (12-14 month survival with CHOP) vs T-cell (6-9 months).
- Complete staging includes CBC, chemistry, thoracic rads, abdominal US, and immunophenotyping.
- CHOP protocol achieves >85% response rates but is not curative; most dogs relapse.
- Hypercalcemia (10-40% of cases) is an oncologic emergency requiring IV fluid diuresis.
- Honest prognosis communication including financial considerations is essential for client care.