Lymphoma is the most common canine cancer making up 7% to 24% of all canine cancers. Lymphoma is a group of cancers originating from the transformation of lymphocytes which are a type of white blood cell that originate from the bone marrow. They are found in our blood stream and our lymphatic system (spleen, lymph nodes, tonsils and lymph vessels). There are two types of lymphocytes – B cells and T cells and each have different roles in fighting infection and regulating our immune system.
The cause of lymphoma is unclear and likely multifactorial. Genetics, previous diagnosis with immune mediated diseases, immunosuppressive medications and environment have been suggested.
Dogs of any breed can be affected but middle-aged to older dogs are more common. Breeds that have increased risk include: Golden Retriever, Labrador Retriever, Boxer, Basset Hound, Saint Bernard, Scottish Terrier, Airedale, Bulldog, Poodle, Bull Mastiff, and Rottweiler.
Clinical Signs (Symptoms)
About 80% of dogs diagnosed with multicentric lymphoma have a classic presentation of generalized peripheral lymphadenopathy (multiple enlarged lymph nodes). Some dogs have only internal lymph node enlargement and may involve the liver and spleen. Some dogs may be completely normal on physical exam but blood work may reveal elevated calcium levels seen with some multicentric lymphoma patients.
Fine-needle Aspiration & Cytology
When enlarged lymph nodes are found, a fine-needle aspirate (FNA) is taken and the cells are placed on a slide and evaluated under the microscope. A fine-needle aspirate is relatively inexpensive, non-evasive and non-painful sampling of the lymph node with a needle and syringe. Most dogs will not react to the sampling or feel pain, it is like receiving a vaccination injection. Large lymph cells called lymphoblasts are the hallmark of this diagnosis. Less commonly, tissue samples are required while under sedation to be evaluated by a pathologist.
Phenotyping identifies the cell line of the cancer – either T Cell or B Cell. This is helpful in determining prognosis as T Cell Lymphoma has a much shorter survival time. An entire lymph node or lymph node biopsy needs to be submitted for phenotyping.
Other Helpful Tests
Other helpful tests in diagnosing and staging lymphoma include Complete Blood Cell Count, Serum Biochemistry Profile, Urinalysis, Abdominal Ultrasound, Chest Radiograph (x-ray), and Bone Marrow Cytology. Your veterinarian will work with you to determine which tests are most helpful while working with you and your budget.
Staging & Prognosis
Multicentric Lymphoma is classified in stages that help the veterinarian determine the extent and severity of the disease to aid in determining prognosis, so the veterinarian and client can work together to make informed decisions about care.
Stage 1 – Only one affected lymph node
Stage 2 – More than one affected lymph node on the same side of the diaphragm
Stage 3 – Multiple affected lymph nodes on both sides of the diaphragm
Stage 4 – Liver and spleen involvement
Stage 5 – Bone marrow or tissue other than lymph node involvement
Substage a – No clinical signs (symptoms)
Substage b – Clinical signs (symptoms)
Phenotype is the best indicator of prognosis with a T Cell lymphoma diagnosis being worse. With B-cell Lymphoma chemotherapy (CHOP Protocol) has about an 80% remission rate with remission durations from 6 to 12 months. 25% of dogs are long-term survivors of greater than 2 years. Chemotherapy with only prednisone results in lower remission of only 50% with duration of 2 to 3 months. Without chemotherapy median survival time is 1 month.
Chemotherapy with the CHOP protocol is the recommend treatment. CHOP chemotherapy includes four medications – cyclophosphamide, hydroxydaunorubicin, oncovin(vincristine) and prednisone. Chemotherapy side effects or toxicity is very low with only 15% to 25% of dogs having some side effects with most dogs tolerating the drugs very well. Chemotherapy is given on an outpatient basis not requiring hospitalization. Most clients feel the dog’s quality of life is improved during treatment.
Referral to the board certified veterinary oncologist is recommended if within your budget. Our preference is the University of Minnesota or the specialty practice BluePearl in the Twin Cities. These veterinarians have an additional 4 years of training in oncology (the study of cancer) with expert knowledge and information on prognosis and the latest treatments.