Lymphoma in Dogs: Symptoms, Diagnosis and Treatment Options

Lymphoma — also known as lymphosarcoma — is a cancer of lymphocytes, a type of white blood cell that plays a central role in the immune system. It is one of the most common cancers in dogs, accounting for approximately 7–24% of all canine neoplasms and roughly 83% of all haematopoietic (blood cell) cancers. Lymphoma most commonly affects middle-aged to older dogs, typically between six and twelve years of age.

"Lymphoma is the cancer I diagnose most frequently in dogs, and it is also one of the most treatable. While a cure is rarely possible, most dogs with lymphoma respond well to chemotherapy and can enjoy many additional months of excellent quality of life. The key is starting treatment promptly once the diagnosis is confirmed." — Dr. Sarah Chen, DVM

Unlike many solid tumours that grow in a single location, lymphoma is typically a systemic disease — it involves the lymphatic system, which extends throughout the entire body. This means that by the time lymphoma is diagnosed, it has usually affected multiple sites, which is why chemotherapy (a systemic treatment) rather than surgery is the primary therapeutic approach.

The good news is that canine lymphoma is one of the most chemotherapy-responsive cancers in veterinary medicine. With appropriate treatment, the majority of dogs achieve remission, and many owners are pleasantly surprised by how well their dogs tolerate chemotherapy compared to their expectations.

Canine lymphoma is classified by anatomical location, and each type presents with different symptoms and carries a somewhat different prognosis. Understanding the type your dog has been diagnosed with helps you know what to expect.

Multicentric Lymphoma (80% of Cases)

Multicentric lymphoma is by far the most common form, accounting for approximately 80% of all canine lymphoma cases. It primarily affects the peripheral lymph nodes — the glands you can feel under the jaw (submandibular), in front of the shoulders (prescapular), in the armpits (axillary), in the groin (inguinal), and behind the knees (popliteal). Most dogs present with generalised, painless lymph node enlargement — often the nodes swell to three to ten times their normal size. In the early stages, dogs may appear completely normal aside from the swollen glands.

Alimentary (Gastrointestinal) Lymphoma

Alimentary lymphoma accounts for roughly 5–7% of canine lymphoma and affects the gastrointestinal tract. Dogs with this form typically present with chronic vomiting, diarrhoea, weight loss, and loss of appetite. It can be challenging to diagnose because these symptoms overlap with many other GI conditions, and the tumours may be diffuse rather than forming distinct masses.

Mediastinal Lymphoma

Mediastinal lymphoma affects the lymph nodes and thymus in the chest cavity. It is relatively uncommon in dogs (unlike cats, where it is more frequent). Affected dogs may present with breathing difficulty, coughing, exercise intolerance, and sometimes fluid accumulation around the lungs (pleural effusion). Hypercalcaemia — elevated blood calcium — is more commonly associated with this form.

Extranodal Lymphoma

Extranodal lymphoma refers to lymphoma arising in organs outside the lymphatic system. It can affect virtually any organ, including the skin (cutaneous lymphoma), eyes, kidneys, nervous system, and nasal cavity. Cutaneous lymphoma is the most common extranodal form, presenting as skin lesions, plaques, or nodules that may be red, scaly, or ulcerated. Each extranodal form has its own unique presentation and prognosis.

The symptoms of lymphoma depend primarily on which form your dog has, though some signs are common across all types. Recognising these symptoms early leads to faster diagnosis and a better treatment outcome.

General Symptoms (All Types)

• Lethargy — reduced energy, less interest in walks or play. Many owners describe their dog as seeming 'not quite right' even before other symptoms become apparent
• Weight loss — progressive loss of body mass despite normal or only slightly reduced appetite. Cancer cells consume significant energy
• Decreased appetite — may be subtle initially, progressing to complete anorexia in advanced cases
• Increased thirst and urination — particularly if hypercalcaemia (elevated calcium) is present, which occurs in approximately 10–15% of lymphoma cases

Multicentric Lymphoma Symptoms

The hallmark sign is painless, enlarged lymph nodes. Owners typically notice firm, round swellings under the jaw, in front of the shoulders, or behind the knees. The nodes often enlarge rapidly over just one to two weeks. In the early stages, most dogs feel completely normal — they eat well, play normally, and show no signs of pain or discomfort. As the disease progresses, dogs develop lethargy, appetite loss, and weight loss.

Alimentary Lymphoma Symptoms

Gastrointestinal involvement causes chronic vomiting, diarrhoea (which may be watery or bloody), abdominal pain, significant weight loss, and loss of appetite. These symptoms often develop gradually over weeks to months, and dogs may initially respond to symptomatic treatment before relapsing.

Mediastinal and Extranodal Symptoms

Mediastinal lymphoma causes breathing difficulty, coughing, and regurgitation due to the mass compressing structures in the chest. Cutaneous lymphoma presents as skin lesions — raised, red, scaly plaques or nodules that may be itchy or ulcerated. Nasal lymphoma causes persistent nasal discharge, sneezing, and facial swelling. Each presentation requires different diagnostic approaches.

A definitive diagnosis of lymphoma requires laboratory confirmation, though an experienced veterinarian can often suspect lymphoma based on physical examination alone — particularly in cases of multicentric lymphoma with obviously enlarged lymph nodes.

Fine Needle Aspirate (FNA)

The fine needle aspirate is typically the first diagnostic step and the fastest route to a diagnosis. Your vet inserts a small needle into an enlarged lymph node and withdraws cells for examination under a microscope (cytology). In most cases of multicentric lymphoma, the aspirate shows a homogeneous population of large, immature lymphocytes — a finding highly suggestive of lymphoma. Results are often available within 24–48 hours if sent to an external laboratory, or sometimes within minutes if your vet performs in-house cytology.

Biopsy and Histopathology

While FNA is often sufficient for diagnosis, a lymph node biopsy provides more detailed information. The entire lymph node (or a portion) is surgically removed and sent for histopathological analysis. This determines the lymphoma subtype and grade — information that helps oncologists predict behaviour and choose the most appropriate treatment protocol. Immunohistochemistry or flow cytometry can further classify the lymphoma as B-cell or T-cell origin, which has significant prognostic implications.

Staging Tests

Once lymphoma is confirmed, staging determines the extent of disease throughout the body. The World Health Organization (WHO) staging system for canine lymphoma ranges from Stage I (single lymph node) to Stage V (bone marrow or blood involvement). Staging typically involves chest X-rays, abdominal ultrasound, complete blood count and biochemistry (including calcium levels), urinalysis, and bone marrow aspirate. Most dogs are diagnosed at Stage III or IV, meaning multiple lymph node regions are affected.

Dogs are further classified as substage 'a' (clinically well) or substage 'b' (clinically unwell) — this distinction is one of the strongest prognostic indicators. Dogs diagnosed at substage 'a' generally respond better to treatment and survive longer.

Chemotherapy is the primary treatment for canine lymphoma, and the CHOP protocol (also known as the University of Wisconsin-Madison protocol) is considered the gold standard. Understanding what this involves helps owners make informed treatment decisions and know what to expect.

What Is CHOP?

CHOP is an acronym for the four drugs used in the protocol: Cyclophosphamide, Hydroxydaunorubicin (doxorubicin), Oncovin (vincristine), and Prednisolone (a corticosteroid). These drugs work through different mechanisms and are administered in a carefully planned rotation over approximately 19–25 weeks. The multi-drug approach is more effective than single-agent chemotherapy because it attacks cancer cells through multiple pathways, reducing the chance of resistance.

Treatment Schedule

During the induction phase (the first four to six months), dogs typically receive intravenous chemotherapy once per week. Prednisolone is given orally at home. After induction, some protocols include a maintenance phase with less frequent treatments, while others stop after the initial course and monitor for relapse. Each appointment takes approximately 30–60 minutes, including a physical examination, blood work, and the infusion itself.

Side Effects and Quality of Life

One of the most important messages for dog owners is that veterinary chemotherapy is designed to preserve quality of life. The doses used are lower than those in human oncology, and serious side effects occur in fewer than 15% of patients. The most common side effects are mild and transient: reduced appetite for one to two days, mild gastrointestinal upset, and temporary lethargy. Hair loss is uncommon in most breeds (though breeds with continuously growing hair, such as Poodles and Old English Sheepdogs, may experience thinning). Most dogs continue their normal daily activities — walks, play, meals — throughout treatment.

Cost Considerations

A full CHOP protocol typically costs between £4,000 and £10,000 (or $5,000–$12,000), depending on the dog's size and geographic location. This is a significant investment, and pet insurance that covers cancer treatment can make a substantial difference. Single-agent protocols (prednisolone alone, or prednisolone with a single chemotherapy drug) are available as lower-cost alternatives, though they generally achieve shorter remission times.

Understanding prognosis helps owners set realistic expectations and make informed decisions about treatment. While individual outcomes vary, the statistics provide a general framework for what to expect.

Survival Rates with Treatment

With the CHOP protocol, approximately 80–90% of dogs with multicentric B-cell lymphoma achieve complete remission (all visible signs of disease disappear). The median survival time is 12–14 months, with approximately 20–25% of dogs surviving beyond two years. Some dogs — roughly 10% — achieve long-term remission lasting three years or more.

Without treatment, most dogs with multicentric lymphoma survive only one to two months after diagnosis. Prednisolone alone (the simplest and least expensive option) provides a median survival of approximately two to three months. Single-agent doxorubicin protocol achieves remission in about 70% of dogs with a median survival of eight to ten months.

Factors Affecting Prognosis

• Immunophenotype — B-cell lymphoma carries a significantly better prognosis than T-cell lymphoma. B-cell dogs have median survival times roughly twice as long as T-cell dogs
• Substage — dogs that are clinically well (substage 'a') at diagnosis respond better than those already showing illness (substage 'b')
• Prior prednisolone use — dogs treated with prednisolone before starting a full chemotherapy protocol may have reduced response rates, which is why veterinarians often prefer to begin CHOP without prior steroid treatment
• Hypercalcaemia — elevated calcium at diagnosis is associated with T-cell phenotype and a worse prognosis

Breeds at Higher Risk

While any breed can develop lymphoma, certain breeds have a documented increased risk. Golden Retrievers are perhaps the most well-known predisposed breed, along with Boxers, Bulldogs, Rottweilers, Bernese Mountain Dogs, Scottish Terriers, and Airedale Terriers. Owners of these breeds should be particularly vigilant about checking lymph nodes during regular veterinary visits and at home. Knowing the lymph node locations and checking them monthly is a simple habit that can lead to early detection.