What is Lymphoma in dogs?

The lymphatic system normally moves fluid throughout the body as well as facilitates the immune system's response to infections. Lymphoma is one of the most common cancers in dogs, accounting for around 10% of all cancers diagnosed in dogs. There are several types of lymphomas that are usually classified by location.

Types of Lymphoma in Dogs

There are several types of Lymphomas in dogs:

1. Multicentric lymphoma: is by far the most common type of lymphoma, up to 80% of lymphoma cases. It is often first noticed in your dog’s peripheral lymph nodes where they become firm and enlarged. From the front of the dog to the tail, there are 5 common areas, but not all 5 are necessarily enlarged.
   1. Submandibular lymph nodes, located under the mandible or lower jaw
   2. Prescapular lymph nodes, located in front of the shoulder
   3. Axillary lymph nodes, located around the armpits
   4. Inguinal lymph nodes, located in the inner upper thigh or groin area
   5. Popliteal lymph nodes, located behind knee on the lower portion of the calf
2. Gastrointestinal lymphoma: this form targets the lymph nodes found around the stomach and intestines. This usually manifests as clinic signs affecting the GI tract, such as poor appetite, vomiting, diarrhea, abdominal pain, constipation, weight loss.
3. Mediastinal lymphoma: this form of lymphoma occurs in the chest cavity where the mediastinal lymph nodes, thymus gland, or both are enlarged and affected. This usually manifests as clinical signs affecting the respiratory tract, such as lethargy, labored breathing, and coughing due to fluid accumulation and direct compression of lung lobes by the enlarged lymph nodes or thymus.
4. Cutaneous lymphoma: this form targets the skin, which usually results in skin masses, nodules, ulcerations, discoloration, and hair loss.
   1. Other extranodal sites where lymphoma can be found (very rare) include kidneys, eyes, central nervous system, and bone.

Common Signs and Symptoms of Lymphoma in Dogs

The symptoms of lymphoma can vary depending on type, location and severity of the cancer. Some common symptoms include:

• Enlarged and firm lymph nodes on the periphery of the dog.
• Lethargy
• Fever
• Decreased appetite
• Weight loss
• Vomiting
• Diarrhea
• Coughing or gagging
• Labored breathing
• Increased water intake and urination

What Causes Lymphoma in Dogs?

There is no known definitive cause for lymphoma, however it is thought that exposure to infectious disease, chemicals, environmental factors, and genetics play a factor. In humans, there has been a link between suppression of the immune system and lymphoma, but it has not been conclusively established in dogs.

Lymphoma can be seen in younger dogs, however, it is most common in middle-aged to older dogs. It is seen more commonly in pure breeds such as Golden Retrievers, Labrador Retrievers, Boxers, German Shepherds, Beagles, Rottweilers, Basset Hounds, and bulldogs.

Diagnosis of Lymphoma in Dogs

Diagnosis usually requires a combination of bloodwork, imaging (such as x-rays and ultrasound), needle aspirates of enlarged lymph nodes, biopsy, and molecular testing. In many cases, your veterinarian can make a diagnosis with a simple needle to aspirate an enlarged lymph node, however other times it can require a biopsy. If lymphoma is confirmed, the next step usually involves further staging and subtyping. These can be considerable extra costs, however it can help inform the prognosis and guide the best treatment options.

Staging is the process of determining if, and where, the cancer has spread. It can also help determine how aggressive the cancer is. This is imaging such as x-rays and ultrasound.

Lymphoma can be classified into 5 stages:

1. Stage One: a single lymph node is involved.
2. Stage Two: multiple lymph nodes in one area of the body are involved.
3. Stage Three: all lymph nodes are involved.
4. Stage Four: all lymph nodes as well as liver, spleen, or lungs are involved.
5. Stage Five: bone marrow is involved.

Subtyping is the process of molecular testing to determine whether the lymphoma is composed of B-cells or T-cells. In general, dogs with T-cell lymphoma have a poorer prognosis than dogs with B-cell lymphoma. T-cell lymphoma is often associated with elevated calcium levels caused by paraneoplastic syndrome, which is often the cause of a dog's excessive thirst and urination. Dogs with elevated calcium levels also tend to have a poorer prognosis.

Treatment for Lymphoma in Dogs

The most effective treatment for canine multicentric lymphoma is chemotherapy. However, in some cases, surgery or radiation therapy may also be recommended depending on the type of lymphoma. A veterinary oncologist can help you decide on the best treatment protocol for your dog.

With chemotherapy, there often is extensive involvement with oncologists, ongoing blood tests during treatment, as well as monitoring of side effects such as lethargy, inappetence vomiting, diarrhea however it achieves the highest rates of remission and longest survival times. Currently the CHOP protocol, named for the chemotherapeutic drugs, is the best protocol. It is a combination of chemotherapy drugs given as weekly IV injections and oral steroids over a 25 week period. The median survival times in dogs receiving chemotherapy are approximately 12 months for B-cell lymphoma and approximately 6–8 months for T-cell lymphoma. Compared to Prednisone alone (a daily oral pill) the typical remission and survival times is 2-3 months. With no treatment, dogs pass away or are euthanized usually within 4–6 weeks.

There is no cure, but the goal is for patients to achieve remission for as long as possible with a good quality of life.

Is it Fair to Put my Dog Through Chemotherapy?

Most dogs tolerate chemotherapy much better than humans. In general, less than 5% of dogs experience chemotherapy side effects when treated for lymphoma and even less lose their hair unlike humans. Chemotherapy doses are usually in lower doses and duration than human counterparts. However there can still be side effects, most commonly are low white blood cell count, decreased appetite, decreased activity level, and mild vomiting or diarrhea that usually only occurs for a few days.

However, dogs do not have the mental awareness that the current side effects from the chemotherapy is for their future benefit. Humans have the benefit of hope, and looking forward to a future of possible remission. This mental strength helps humans possibly endure more momentary pain for future benefit whereas dogs live in the moment. If serious side effects do occur and you believe their quality of life has diminished substantially, it is important to talk with your veterinarian. It may be possible to reduce the dose or frequency to lessen the side effects of chemotherapy while still maintaining therapeutic levels to treat the cancer or potentially stop treatment all together. Ultimately the hope is to increase the longevity and quality of their life so you can have more time with your beloved dog. We recognize it is also important to allow your dog to continue living their day to day life as normally as possible.

What is the Prognosis of Dogs with Lymphoma?

A dog's prognosis will vary greatly depending on the type of lymphoma, staging, and subtyping. However here are some median survival times:

• High-grade B-cell lymphoma has a better prognosis than high-grade T cell lymphoma.
• Median survival time for dogs with multicentric B-cell lymphoma receiving CHOP chemotherapy protocol is 11-13 months.
• Median survival time for dogs with multicentric T-cell lymphoma receiving CHOP chemotherapy protocol is 6-8 months.
• Oral prednisone alone is 2-3 months.
• No treatment is 4-6 weeks

Management of Dogs with Lymphoma

While the long-term prognosis for canine lymphoma is poor, treatments in consultation with your veterinarian can help your dog get into remission. The goal of remission is to provide many months of disease free good quality of life. Remission can be complete or partial, with complete remission being that all signs of disease have disappeared, while partial remission means at least 50% of the signs have disappeared.

It is impossible to predict how long your pet will remain in remission, however once remission is lost, clinical signs start to develop, the previous chemotherapy protocol will not be effective and will likely need new chemotherapeutic drugs as a “rescue protocol.”

Unfortunately, there is no prevention, vaccine, or cure for lymphoma. Therefore routine veterinary visits especially, senior dogs are important for early detection of enlarged lymph nodes. In addition to routine veterinary care, it is important to provide great nutrition, regular exercise, avoid environmental chemicals/ toxins, and reduce obesity.