October 11, 2019 – Lymphoma is one of the most common cancers of dogs and for a long time was treated as a single disease. The development of sophisticated diagnostic techniques allowed researchers to look at lymphoma more closely and they quickly learned there are many different subtypes of the disease, each with its own unique features and treatment response.
This discovery confirmed what many veterinary oncologists already knew – patient outcomes were varied even when their cancers appeared the same.
We’re still learning more about each type of lymphoma, but it’s important for dog owners to have the latest information in case their dog is diagnosed with this common cancer.
Let’s start with the most basic division of lymphoma type – whether the cancer arises from T cells or B cells. Lymphocytes are a type of white blood cell and an important part of the immune system. Most lymphocytes are either B cells, which produce antibodies, or T cells. T cells are further divided into two types – helper T cells which provide signals to other cells of the immune system to amplify or suppress an immune response, and cytotoxic (killer) T cells which help kill abnormal cells. Lymphoma can arise when either B cells or T cells start to divide uncontrollably.
Knowing whether a lymphoma is predominantly B cell or T cell in origin is important for prognosis and treatment. Each form has aggressive and less aggressive subtypes, and diagnostic testing can provide important additional information.
One way to determine the lymphoma subtype is a test called flow cytometry during which fresh cells are aspirated from a suspect lymph node or organ for review. Your veterinarian may also want to perform a lymph node biopsy and send the specimen to a pathologist for additional evaluation. This step is more involved since it requires tissue collection, but for some subtypes of lymphoma it is the only way to get an accurate diagnosis.
Once diagnostic testing is performed, one of several subtypes of lymphoma will be identified. Some of the most common are:
- Peripheral T cell lymphoma – this common form of lymphoma usually starts with enlarged lymph nodes but often affects other organs. Dogs with this form of lymphoma have an average survival time of around seven to eight months with chemotherapy.
- Diffuse large B cell lymphoma – this is the most common form of lymphoma in dogs. This form of lymphoma presents in the same way as T cell lymphoma but prognosis with chemotherapy is much better, with average survival times of 12 to 24 months.
- T zone lymphoma – unlike peripheral T cell lymphoma, this type of lymphoma has an excellent long-term survival, with many dogs living three or more years, sometimes with no chemotherapy.
- Precursor lymphoma/leukemia – tumors derived from immature lymphocytes are the most aggressive form, with median survival times measured in days, even with treatment. Cytology and histology are unable to distinguish immature neoplasms from mature B and T cell lymphoma. This distinction can only be made by flow cytometry.
Other less common types of lymphoma include cutaneous lymphoma, nodal marginal zone lymphoma and follicular lymphoma. These types of lymphoma have a broad range of survival times and all require a biopsy sample for diagnosis.
One of the challenges faced by veterinary oncologists is the lack of large numbers of cases of a specific lymphoma subtype. For example, splenic marginal zone lymphoma is a rare type of lymphoma. There are fewer than 100 reported cases of this type of lymphoma but these patients have a very good long-term prognosis. However, it requires many more diagnoses for veterinarians to feel secure when discussing prognosis with a concerned pet owner.
The Golden Retriever Lifetime Study is a unique opportunity to study lymphoma in a prospective, real-time way. We currently have 43 dogs diagnosed with lymphoma but only half of these patients have had a subtype determination.
There are many reasons for determining subtype:
- Different forms of lymphoma have different risk factors – understanding the lymphoma subtype will help us better understand causes
- By subtyping canine lymphomas, we can draw parallels to their human counterparts. Dogs can benefit from new therapies developed in human patients
- Different forms of lymphoma have dramatically different outcomes, and subtyping can help inform owner decisions about treatment
We’re proud to announce that we’ve partnered with Dr. Anne Avery’s laboratory at Colorado State University to make it easier and less expensive to get flow cytometry subtyping for Golden Retriever Lifetime Study dogs diagnosed with lymphoma. This facility is the largest lab in the United States that performs this analysis and team members are experts in interpreting results, which are reported back to the submitting veterinarian.
For more information, contact the Study team at 855-4GR-DOGS (855-447-3647). You and your veterinarian also can download our new biopsy instruction booklet which has detailed instructions on sample collection and shipping.