Lymphoma, also known as lymphosarcoma, is a cancer that arises from lymphocytes, which are key immune system cells found throughout the body. Because lymphocytes are present in nearly every organ, lymphoma can develop almost anywhere, but it most commonly affects the lymph nodes, spleen, liver, and bone marrow.

There are several types of lymphoma in dogs, classified by location:

• Multicentric lymphoma: By far the most common form, accounting for approximately 80% of canine lymphoma cases. It involves the external lymph nodes throughout the body and is typically the type people refer to when they say "lymphoma." It usually presents as painless swelling of multiple lymph nodes.
• Alimentary (gastrointestinal) lymphoma: Affects the stomach, intestines, and associated lymph nodes. It accounts for about 5-7% of cases and may cause vomiting, diarrhea, weight loss, and decreased appetite.
• Mediastinal lymphoma: Develops in the lymph nodes and thymus within the chest cavity. It can cause difficulty breathing and fluid accumulation in the chest.
• Extranodal lymphoma: Occurs in organs outside the lymphatic system, including the skin, eyes, kidneys, lungs, and central nervous system.

Lymphoma can further be classified by the type of lymphocyte involved: B-cell or T-cell. B-cell lymphoma is more common and generally responds better to treatment, with longer survival times. T-cell lymphoma tends to be more aggressive and more challenging to treat, though many dogs still benefit from therapy.

Lymphoma can affect any breed at any age, but it is most commonly diagnosed in middle-aged to older dogs (6-9 years). Breeds with a higher incidence include Golden Retrievers, Labrador Retrievers, Boxers, Bulldogs, Rottweilers, and Scottish Terriers. The cause of lymphoma in most cases is unknown, though genetic predisposition plays a role.

The signs of lymphoma depend on the type, but multicentric lymphoma, the most common form, often has a very characteristic presentation that many dog owners discover by chance.

Common signs of multicentric lymphoma:

• Swollen lymph nodes: The most typical first sign. You or your veterinarian may notice firm, painless, enlarged lumps under the jaw (submandibular), in front of the shoulders (prescapular), or behind the knees (popliteal). The swelling can appear suddenly and may be dramatic, with lymph nodes growing to several times their normal size.
• In early stages, many dogs feel completely normal. They may eat well, play normally, and show no signs of illness despite having significantly enlarged lymph nodes. This is one of the unique and somewhat deceptive characteristics of lymphoma.
• As the disease progresses: Lethargy, decreased appetite, weight loss, increased thirst and urination, vomiting, diarrhea, and difficulty breathing may develop.

Diagnosis typically begins with a fine-needle aspirate of an enlarged lymph node, a quick, minimally invasive procedure where cells are collected with a needle and examined under a microscope. In most cases, this provides a definitive diagnosis. Additional testing may include:

• Blood work and urinalysis to assess overall health
• Chest X-rays and abdominal ultrasound to evaluate internal lymph nodes and organs
• Bone marrow aspirate to check for marrow involvement
• Immunophenotyping to determine whether the lymphoma is B-cell or T-cell (this affects prognosis and may influence treatment decisions)

Staging uses these tests to determine how far the cancer has spread, using a system from Stage I (single lymph node) to Stage V (bone marrow or blood involvement). Most dogs are diagnosed at Stage III or IV, but even advanced-stage lymphoma often responds well to chemotherapy.

Lymphoma is one of the most responsive cancers to chemotherapy in veterinary medicine, and treatment can significantly extend survival while maintaining an excellent quality of life. Understanding the treatment options helps you make the best decision for your dog and your family.

CHOP-based chemotherapy protocol: The gold standard treatment is a multi-drug protocol similar to the CHOP regimen used in human medicine. It typically involves weekly visits to a veterinary oncologist over 19-25 weeks, with different chemotherapy drugs administered in a rotating schedule. This protocol achieves complete remission (disappearance of all detectable cancer) in approximately 80-90% of dogs. Median survival with CHOP is 10-14 months, with approximately 20-25% of dogs living two years or longer.

Single-agent protocols: For families who prefer a simpler approach, single-drug protocols using doxorubicin are available. Doxorubicin alone achieves remission in about 65-75% of dogs, with median survival of approximately 6-9 months. This option involves fewer vet visits and lower overall cost.

Oral chemotherapy (CCNU/lomustine): An oral medication given every 3 weeks, often used as a rescue protocol after relapse from CHOP, or as a first-line option for families who prefer minimal hospital visits.

Prednisone alone: Steroid therapy can provide temporary improvement, shrinking lymph nodes and making dogs feel better for a period of 1-2 months. Median survival with prednisone alone is approximately 1-2 months. This option is sometimes chosen for financial reasons or when a dog is not a candidate for more intensive treatment.

A critical point about chemotherapy in dogs: dogs tolerate chemotherapy far better than humans do. The protocols are designed to maintain quality of life, not just extend it. Approximately 80-85% of dogs experience no significant side effects. When side effects do occur, they are usually mild and self-limiting, including a few days of decreased appetite or mild gastrointestinal upset. Severe side effects requiring hospitalization occur in less than 5% of treated dogs. Your dog will not lose their fur (though breeds with continuously growing coats, like Poodles, may experience thinning).

Understanding the prognosis for canine lymphoma helps you set realistic expectations while appreciating the genuinely good time that treatment can provide.

Without any treatment: Average survival from the time of diagnosis is approximately 4-6 weeks. During this time, the lymph nodes continue to grow, and dogs eventually become ill from organ involvement.

With CHOP chemotherapy: Median survival is 10-14 months, with 20-25% of dogs achieving 2-year survival. During remission, most dogs feel completely normal and enjoy all their usual activities.

Factors that influence prognosis:

• B-cell lymphoma generally has a better prognosis than T-cell
• Dogs that are clinically well at diagnosis tend to do better than those that are already sick
• Dogs that achieve complete remission have longer survival times
• Substage (whether the dog is sick or well at diagnosis) is one of the strongest prognostic factors

Most dogs with lymphoma eventually relapse after initial treatment. When relapse occurs, the cancer can often be put back into remission with a different chemotherapy protocol, though second remissions are typically shorter than the first. Each subsequent remission tends to be progressively shorter, and eventually the cancer becomes resistant to treatment.

Throughout treatment, quality of life should be the guiding principle. The goal is not to fight cancer at all costs but to give your dog the maximum amount of good time. For most dogs, the months of remission are genuinely wonderful months. They play, they eat, they go for walks, they snuggle on the couch. They do not know they have cancer, and their days are filled with the ordinary joys that make a dog's life complete.

When the time comes that treatment is no longer working, that the bad days begin to outnumber the good, many families find peace in knowing they gave their dog every good day possible and loved them fully through every one of them.