It can be overwhelming hearing that your fur baby has lymphoma. One moment you may notice a swollen lymph node or a change in your dog’s energy level, and the next you’re facing a difficult decision about testing and treatment.

Lymphoma is one of the most common and one of the most treatable cancers in dogs. Depending on the type of lymphoma, many dogs respond well to therapy and can enjoy an excellent quality of life for months or even years after diagnosis.

In this blog, we’ll explain what canine lymphoma is, the different types of lymphoma, early warning signs, how veterinarians diagnose it, available treatment options, prognosis, and how supportive care may help improve your dog’s comfort throughout treatment.

What Is Canine Lymphoma?

Lymphoma is one of the most frequently diagnosed malignancies in dogs. It is a cancer that develops from lymphocytes, a type of white blood cell that plays a vital role in the immune system. Lymphocytes are found in many parts of the body, including the lymph nodes, spleen, liver, bone marrow, gastrointestinal tract, skin, and many other organs; for that reason, lymphoma may be considered a systemic disease.

What Causes Lymphoma in Dogs?

Unfortunately, there is no single answer to this question. Some evidence suggests that lymphoma can develop through a combination of environmental influences and genetic susceptibility.

Some of the potential contributing factors include:

• Genetic predisposition
• Age (most commonly middle-aged to older dogs)
• Breed predisposition
• Chronic immune dysregulation
• Environmental exposures
• Rare infectious causes

Certain breeds appear to have a higher risk, such as:

• Boxer
• Golden Retriever
• Labrador Retriever
• Rottweiler
• Saint Bernard
• Scottish Terrier
• Bullmastiff

However, it is important to note that although these breeds may be predisposed, lymphoma can develop in any breed. Lymphoma is also not contagious and is generally not caused by anything pet owners did or failed to do.

Signs of Lymphoma in Dogs

The signs of lymphoma can vary depending on the type and location it is affecting
Many dogs initially appear completely healthy. Early signs may include:

• Swollen lymph nodes
• Mild lethargy
• Activity that is reduced
• Decreased appetite
• Weight loss
• Increased drinking or urination

As lymphoma progresses, dogs may develop:

• Marked lethargy
• Progressive weight loss
• Lack of appetite
• Fever
• Vomiting
• Diarrhea
• Difficulty breathing (mediastinal lymphoma)
• Abdominal enlargement
• Persistent skin lesions (cutaneous lymphoma)

When Should You See Your Veterinarian?

If you observe any persistent, enlarged lymph nodes, your fur baby should be examined by your veterinarian as soon as possible. Early diagnosis may improve quality of life.

Types of Lymphoma in Dogs

Canine lymphoma is a diverse group of cancers that can be classified according to anatomical location, cell type, grade, and biological behavior. Here we will list the most common:

• Multicentric Lymphoma: This accounts for most of all canine lymphoma cases. It primarily affects the peripheral lymph nodes, spleen, and liver. Some dogs can present with enlarged lymph nodes but otherwise may appear surprisingly normal during the early stages of the disease. 
• Alimentary (Gastrointestinal) Lymphoma: This form develops in the digestive tract. Some of the most common signs are vomiting, weight loss, reduced appetite, low protein levels, chronic diarrhea or constipation.  Definitive diagnosis often requires abdominal ultrasound and intestinal biopsy.
• Mediastinal Lymphoma:  This form of lymphoma affects the chest cavity, and some of the signs are rapid breathing, exercise intolerance, coughing, pleural effusion, etc.
• Cutaneous lymphoma: This form affects the skin, and some of the signs include red plaques, thickened skin, hair loss, scaling, non-healing skin lesions, and Itching. For this type of cancer, definitive diagnosis usually requires skin biopsies.
• Extranodal Lymphoma: These are types of lymphomas that occasionally arise outside the lymphatic system, such as in the eyes, kidneys (renal lymphoma), central nervous system, nasal cavity, bones, etc.

Phenotype (B-Cell vs T-Cell Lymphoma)

Another important way to classify canine lymphoma is by the phenotype of the lymphocyte present. Most lymphomas originate from either B lymphocytes (B cells) or T lymphocytes (T cells), which are important components of the immune system.

Knowing whether a dog has B-cell or T-cell lymphoma can be helpful to better understand the expected clinical behavior of the disease, estimate prognosis, and select the most appropriate treatment.

B-Cell Lymphoma

The most common immunophenotype in dogs. Many of the common high-grade B-cell lymphomas respond well to chemotherapy and are generally associated with longer remission and survival times than high-grade T-cell lymphoma. Remission refers to a period during which the clinical signs and detectable evidence of lymphoma have partially or completely disappeared following treatment.

T-Cell Lymphoma

T-cell lymphoma is less common compared to B-cell lymphoma. Unfortunately, many high-grade T-cell lymphomas may behave more aggressively and have shorter remission and survival times. However, this is not true for every T-cell lymphoma.

Biological/Clinical Behavior: How Fast Does the Lymphoma Progress?

Another very important part of understanding lymphoma in dogs is how fast the disease progresses. B-cell and T-cell lymphomas can have different biological/clinical behaviors, ranging from slow progression to a more aggressive disease.

Indolent lymphoma grows slowly and may progress over months and, in some cases, years. These lymphomas can be either B- or T-cell. One example is T-zone lymphoma, which is a slow-growing T-cell lymphoma. Some low-grade B-cell lymphomas can also behave indolently. Some dogs with these forms may feel well for long periods, and depending on the individual case, very close monitoring may be recommended before treatment is initiated.

However, high-grade lymphoma progresses and spreads much faster. Both B- and T-cell lymphomas can be high-grade, although high-grade T-cell lymphoma is often associated with a more aggressive clinical behaviour.

This is why B-cell does not automatically mean a good prognosis, and T-cell does not automatically mean a poor prognosis. The lymphoma subtype, grade, location, stage, clinical signs, and response to treatment all help determine how the disease is likely to behave and the best approach for each pet.