Lymphoma in dogs is a group of 30+ different types of cancer that can develop from cells called lymphocytes, a relative of red blood cells. These cancers often begin in the lymph nodes or other tissues of the lymphatic system, including the lymphatic vessels, spleen, tonsils, thymus, or bone marrow.
However, they can start from any tissue as lymphocytes are present throughout the body to fight and prevent infections and disease. Lymphoma, like other canine and feline cancers, are cellular diseases that occur when lymphocytes reproduce uncontrollably in an area requiring us to take our dogs to the veterinary office for treatments that will target those cells.
Lymphoma accounts for 15-20% of cancer diagnoses in dogs, and there are 10+ dog breeds with a genetic predisposition to lymphomas, including Chow Chow, Basset Hound, Scottish, Airedale, West Highland White, Yorkshire, and Bull Terriers, Golden Retriever, English Bulldog, German Shepherd, Beagle, Rottweiler, Saint Bernard, and Poodle.
Interesting fact: Male dogs are usually diagnosed at younger ages than female dogs.
When your veterinarian diagnoses your pet with lymphoma, they will count your dog's white blood cells and then separate them into two main categories/types. The lymphocytes involved and their location in the body determine what type of lymphoma your pet has.
For example, 80% of lymphomas in dogs are called Diffuse B Cell multi-nodal lymphoma. This means the type of cancerous lymphocytes involved are B cells, and they are located in multiple different lymph nodes throughout the body. Dogs with multi-nodal lymphoma are treated with chemotherapy, and 50% will survive past 8-13 months.
Interesting Fact: Multinodal lymphoma in Dogs is considered an animal model for non-Hodgkins lymphoma in humans, which is newly diagnosed in 80,000 people every year. They are alike in both symptoms and how chemotherapy drugs react similarly in humans and our canine companions.
The Stages of Lymphoma in Dogs
There are five stages of lymphoma, and your veterinarian can run a combination of blood tests, urinalysis, imaging (X-ray or unstrasound), and taking tissue samples to determine what stage your dog is at.
The World Health Organization (learn more here at Merck Veterinary) has separated the progression of lymphoma in dogs into 5 stages:
- Stage 1: Limited to a single lymph node or lymphoid tissue in a single organ (excluding bone marrow).
- Stage 2: Multiple lymph nodes within a region (with or without tonsil involvement).
- Stage 3: Lymph node involvement throughout the body above and below the diaphragm.
- Stage 4: Stages 1, 2, or 3 AND involvement of organs in the abdomen (research by Jenny Cassibry Fisher, RVT, VTS) such as the liver or spleen. At this stage, pets are often sick, with some symptoms including fever, uveitis, and hypercalcemia (elevated calcium levels).
- Stage 5: Any of the previous stages with inclusion in the blood and involvement of bone marrow or multiple organ systems (beyond the system where the lymphoma started), often including the nervous system such as the brain.
Types of Cells
There are 2 main types of lymphocytes:
- B cells: create antibodies
- T cells: the part of your immune system that directly attacks infected cells from bacteria, fungi, viruses, or even mutated DNA (cancer).
Two-thirds of dogs diagnosed with lymphoma have B cell lymphoma, and one-third are classified as T cell. T cell lymphoma has a higher incidence in certain dog breeds, including Boxers, golden retrievers, Australian shepherds, Asian lap dogs, and the Siberian husky. Lymphomas that have cancerous T and B cells simultaneously are rare.
Cells Size Matters
Your veterinarian may classify your cat or dog’s lymphoma as small-cell or large-cell.
- Large Cell lymphomas have T or B cells larger than normal T or B cells
- Small Cell lymphomas have T or B cells smaller than the normal T or B cell
Lymphomas with smaller cells can indicate a slower replication cycle and less aggressive cancer compared to large-cell lymphomas. There are exceptions to this, like diffuse small-cell B-cell lymphoma, which is considered a high-grade (aggressive) lymphoma in dogs despite having smaller cells compared to normal B cells. Classifying the cells into large or small subtypes can help your veterinarian map out possible treatment plans and outcomes with you.
Grading Lymphoma (How the Cells Compare to Healthy Ones)
Lymphoma behavior is divided into high-grade and low-grade categories based on your pet’s symptoms and the results of previous testing.
~75% of dogs are diagnosed with intermediate to high-grade lymphoma, which is typically aggressive and requires aggressive treatment.
In Dogs, the most common form of high-grade lymphoma is multi nodal diffuse B cell lymphoma, followed by alimentary (lymphoma of the intestines) and mediastinal (lymphoma in the chest). Without treatment, dogs with T or B cell high-grade lymphomas have an average survival of 4-6 weeks.
~5-29% of lymphomas in dogs are low-grade lymphomas, which are slow-growing and can take months or years for your pet to have symptoms. Other names for low-grade lymphomas are lymphocytic lymphoma and indolent lymphoma, and this kind usually starts in the lymph nodes or spleen.
If the cancer cells are in the blood, your veterinarian may call it chronic lymphocytic leukemia (CLL). Although rare, a low-grade lymphoma might turn into a high-grade lymphoma at any time, particularly in B-cell lymphomas.
High-Grade and Intermediate-Grade Lymphoma Symptoms
When brought to their veterinarian, dogs with intermediate—to high-grade lymphomas often display outward symptoms of the disease.
These symptoms may include:
- Enlargement of any lymph node (found under the lower jaw, in the neck, armpits, inside of the groin, and behind your pet's knees). They may feel hard to touch and are often not painful when pressed.
- Weight loss
- Vomiting
- Diarrhea
- Decreased Appetite
- Gastrointestinal lesions/growths
- Coughing
- Shortness of breath
- Growths/lesions in the chest
- Organ failure
- Organ enlargement (usually named as affected organ + megaly, for example, kidney enlargement would be renomegaly)
- Areas of Swelling
- Death
Treatment for Intermediate and High-Grade Lymphomas
After diagnosis with an intermediate or high-grade lymphoma, your veterinarian may suggest your pet immediately start on one of several chemotherapy protocols.
If your pet has a mass, surgery may be used to completely remove affected tissues. 50% of pets will experience some level of remission and survive for 6-12 months post-chemotherapy. 90% of dogs with treatment see complete remission, which means testing can no longer detect any cancer cells! This remission can last from months to years.
Important Fact: Gloves should be worn when administering any chemotherapy drugs, and pregnant people and animals should avoid them.
Current chemotherapy protocols for Intermediate and High-grade lymphomas in dogs include:
- CHOP (Cyclophosphamide, hydroxydaunorubicin, vincristine, and prednisone) is the most popular protocol for dogs, with 79-100% achieving complete remission for at least a year
- COP (vincristine, cyclophosphamide, and prednisone)
- MOPP (Mechlorethamine, vincristine, procarbazine, and prednisone) involves both injections and medications you can give your dog at home.
- LOPP (lomustine (CCNU), vincristine, procarbazine, and prednisolone) is specialized for T-cell lymphomas and has similar survival times compared to those treated with CHOP for dogs.
Other treatments include:
- Laverdia-CA1 (verdinexor tablets): A 2024 study found this was also 75% effective for canine T-cell lymphoma. A clinical trial at the University of Missouri is exploring whether this medication will work for Cutaneous epitheliotropic lymphoma.
- A bone marrow transplant may also be a possibility for dogs with B-cell lymphomas.
Important Note: Disclose all medications to your veterinarian or dog’s caregiver! Cyclophosphamide works by relying on the bacteria living in your pet’s intestines. So, if your pet has been taking antibiotics this drug may be less effective.
Potential Side Effects of Treatment of High and Intermediate-Grade Lymphomas
Dogs tolerate chemotherapy drugs much better than humans, with over 80% being able to manage any side effects at home.
Some side effects of treatment include:
- Coat changes, including fur loss
- Lack or increase in appetite
- Diarrhea or bloody diarrhea
- Bloody urine
- Bruising
- Increased risk of secondary infections like skin mites
- Shortness of breath
- Agitation
- Facial Twitching
- Seizures
- Increased urination
- Blisters on the skin
- Extravasation - this is a medical emergency where swelling, color changes (including redness), and pain are present at the drug injection site due to the medication leaking into surrounding tissue.
If your pet is experiencing side effects, don’t be afraid to consult with your vet immediately. Just because a side effect is attached to a medicine does not mean our pets have to feel it!
Low-Grade Lymphoma Symptoms
Although often not present at the initial vet visit, symptoms of low-grade lymphomas may include:
- Gradual enlargement of any lymph node (found under the lower jaw, in the neck, armpits, inside of the groin, and behind your pet's knees). They may feel hard to touch and are often not painful when pressed.
- Weight loss
- Vomiting
- Diarrhea
- Decreased Appetite
- Skin parasites like Demodex mites
- Death
Treatment for Low-Grade Lymphoma
Due to the slow-growing nature of this type, your pet may not immediately be started on medication.
Once you and your vet choose to start treatment, your options may include:
- Prednisone - a corticosteroid. For some animals, treatment with corticosteroids alone can lead to remission for 1-2 months but can result in multi-drug resistance. This medication may sound familiar as it is also used to treat human illnesses, including cancer. However, the dosage is different, so it is important to only take as prescribed by a veterinarian.
- Chlorambucil - a chemotherapy drug. It works by binding to the DNA in lymphocytes, and damaging it so the cancerous cell can no longer replicate itself. Often taken in combination with prednisone.
Side Effects of Treatment of low-grade lymphomas
Regular visits with your vet will help you and your veterinarian track any side effects your pet may be experiencing from taking prednisone and/or chlorambucil.
Possible side effects include:
- Coat changes, including fur loss
- Lack or increase in appetite
- Diarrhea or bloody diarrhea
- Bruising
- Secondary infections
- Shortness of breath
- Agitation
- Facial Twitching
- Seizures
- Increased urination
Lymphoma Prevention and Symptom Relief From Home
As with any changes to your dog’s routines, always talk to their veterinarian before trying any of the options below. This section is so you can go to them prepared with questions to ask and options you want to know more about.
There are other things you can do at home to potentially prevent lymphoma and provide relief for symptoms of this cancer and its treatments.
For pets that are drinking (and peeing) more, allowing them free access to water and frequent potty breaks after treatment as this can help manage their comfort levels. Fasting before giving chemotherapy drugs may lessen the chance of your dog throwing up or having diarrhea post-treatment as there is less to come out.
Adding a probiotic and/or prebiotic to your dog's diet to help regulate its microbiome can help with vomiting and diarrhea and help prevent cancer. Imbalances in the bacteria and fungi in the gut microbiome may cause cancer, including lymphoma. A prebiotic or probiotic can help reduce overgrowth of any one inhabitant of the intestines, improving GI symptoms along with it.
Cannabinoids may help increase appetite and help with pain, while also increasing treatment effectiveness. One study CBD found CBD helped inhibit cell replication and accelerate the death of cancerous cells in canine B-cell lymphoma. Another study published in 2024 showed CBD can inhibit the growth of B and T cell canine lymphomas.
CBD has been used as a treatment for epilepsy in dogs and could be an option for those pets affected by seizures as a side-effect for treatment. And there are CBD products for dogs that support cellular health.
75% of dogs have a mutation in their MDMR (Multi-Drug Resistance) gene, which causes them to have worse reactions to certain chemotherapy medications, including Vincristine, Vinblastine, Doxorubicin, and Paclitaxel. Any dog may have this mutation, but it is more common in herding dogs such as Collies and the American, German, and Australian Shepherds. One way to lessen your pet's side effects is to have them tested for this genetic mutation before treatment.
Lymphoma is one of the most common cancer types in dogs. It is well-studied and there are multiple treatment options available, even for the most aggressive types. By working closely with your veterinarian’s team you can help your pet have a good quality of life, even after a lymphoma diagnosis and during treatment.
