Hey there, pet parents. A diagnosis of cancer is always scary, but it's important to know that not all cancers are created equal. Today, we're going to talk about one of the most common cancers in dogs: Lymphoma. While lymphoma is a serious and ultimately life-limiting disease, the great news is that it is one of the most treatable and rewarding cancers to manage in veterinary medicine.
What is Lymphoma?
Lymphoma is a cancer of a type of white blood cell called a lymphocyte. Lymphocytes are a key part of the immune system, and they are found throughout the body, especially in the lymph nodes, spleen, and bone marrow.
Because lymphocytes travel all over the body, lymphoma is considered a systemic disease right from the start. There are many different types of lymphoma, but the most common form by far in dogs is multicentric lymphoma, which affects the lymph nodes.
Spotting the Signs of Lymphoma
The most common sign of multicentric lymphoma is something an owner can find at home.
- •Swollen Lymph Nodes: The hallmark sign is the discovery of one or more large, firm, non-painful lumps under the dog's neck, in front of their shoulders, or behind their knees. These are the peripheral lymph nodes. A normal lymph node is small and difficult to feel, but a lymph node affected by lymphoma can be the size of a golf ball.
Many dogs with lymphoma will otherwise feel completely fine in the early stages. This is called "Stage A" lymphoma (for "asymptomatic"). As the disease progresses, the dog may start to feel sick. This is "Stage B" lymphoma (for "B-cell" like symptoms).
- •Lethargy
- •Decreased appetite
- •Weight loss
Lymphoma can also affect other organs, leading to different signs. For example, GI lymphoma can cause vomiting and diarrhea, while skin lymphoma can cause itchy skin lesions.
How Vets Diagnose Lymphoma
If your vet finds enlarged lymph nodes, they will recommend a very simple and quick procedure to get a diagnosis.
- •Fine Needle Aspirate (FNA): Your vet will use a small needle to take a sample of cells from the enlarged lymph node. They will then look at the cells under a microscope. In a dog with lymphoma, the slide will be packed with large, abnormal lymphocyte cells. An FNA can provide a diagnosis in over 90% of cases.
- •Biopsy: In some cases, a surgical biopsy of the lymph node may be needed to get a definitive diagnosis and to determine the specific type of lymphoma (B-cell vs. T-cell), which can affect the prognosis.
Staging: What's a "Stage" and "Substage"?
Once lymphoma is diagnosed, your vet or a veterinary oncologist will recommend "staging" tests to determine the extent of the cancer in the body. This usually involves bloodwork, a urinalysis, chest X-rays, and an abdominal ultrasound.
- •The Stage (I-V): Refers to how far the cancer has spread. Most dogs are Stage III or IV at diagnosis.
- •The Substage (a or b): Refers to how the patient feels. Substage 'a' means they feel well, while substage 'b' means they are sick.
The most important piece of staging information is determining if it is B-cell or T-cell lymphoma. This is done through special testing on the aspirate or biopsy sample. B-cell lymphoma is more common and has a much better prognosis than T-cell lymphoma.
Treatment: The Goal is Remission
The treatment of choice for multicentric lymphoma in dogs is chemotherapy. It's important to understand that chemotherapy in dogs is very different from in people. The goal is not to cure the cancer (which is rarely possible), but to put it into remission and to give the dog a great quality of life for as long as possible.
The doses of chemotherapy drugs used in dogs are much lower than in people, so the side effects are much less severe. Most dogs tolerate chemotherapy very well. They don't usually lose their hair (though some breeds can), and while they might have a day or two of mild nausea or lethargy after a treatment, most of them feel great.
The CHOP Protocol
The gold standard chemotherapy protocol for lymphoma is called the CHOP protocol. It's a multi-drug protocol that involves a weekly rotation of different chemotherapy drugs (Cyclophosphamide, Hydroxydaunorubicin/Doxorubicin, Oncovin/Vincristine, and Prednisone) for several months.
Prognosis: It's All About Remission
Lymphoma is very responsive to chemotherapy. With a multi-drug protocol like CHOP, about 80-90% of dogs will achieve a complete remission. This means the lymph nodes go back to a normal size and the dog feels completely normal.
The prognosis depends on the cell type:
- •For B-cell lymphoma (the "better" kind): The average remission time is about 9-12 months, and the average survival time is about 12-14 months.
- •For T-cell lymphoma (the "terrible" kind): The prognosis is much poorer, with an average survival time of only about 4-6 months.
Without any treatment, the average survival time for a dog with lymphoma is only about 1-2 months.
While lymphoma is not a curable disease, chemotherapy offers a fantastic opportunity to give your dog a whole extra year of happy, high-quality life. It's a journey that many owners find to be incredibly rewarding.
Sources & Further Reading:
- •American College of Veterinary Internal Medicine - Lymphoma in Dogs
- 1VCA Animal Hospitals - Lymphoma in Dogs