What is indolent lymphoma?
Indolent lymphoma is a group of low-grade lymphomas that are slowly progressive and most don't benefit from treatment with chemotherapy. These lymphomas comprise up to 1/3 of all canine lymphoma.
Since the disease course is vastly different from the more common and more aggressive large cell lymphoma, an accurate diagnosis is essential.
Examples of indolent lymphoma include t zone lymphoma, marginal zone lymphoma, mantle cell and follicular lymphoma.
T zone lymphoma actually accounts for 12% of all lymphoma in dogs and is frequently misdiagnosed.
Forty percent of dogs that develop t zone lymphoma are golden retrievers - it is most common in this breed. The median age at diagnosis (half are older and half are younger) is 10 years; most dogs have enlarged lymph nodes and an elevated lymphocyte count on blood work.
Typically a patient will present with one or more enlarged large lymph nodes that can be felt on physical exam or an enlarged spleen.
What is the cause of indolent lymphoma?
A recent paper showed that t zone lymphoma occurred significantly less frequently in golden retrievers that had a history of hypothyroidism and omega-3 fatty acid supplementation, and more frequently in those that had a history of mange. More work is being done to fully understand this disease.
How do we diagnose indolent lymphoma?
Whereas making a diagnosis of large cell (regular) lymphoma is typically fairly straightforward (aspirate an enlarged lymph node), this method will not give you a definitive diagnosis of indolent lymphoma.
To diagnose indolent lymphoma, typically flow cytometry is used (this involves sending a special test to Colorado State using a lymph node sample) or by removing a lymph node, and having it evaluated with histopathology and special stains for B and T cells (flow cytometry is less invasive).
How do we treat indolent lymphoma?
Studies have shown that this group of diseases does not appear to benefit from chemotherapy (dogs don't live longer if they receive chemotherapy treatment).
If the patient has a mass in the spleen, removing the spleen might be recommended. We typically recommend this procedure (splenectomy) for any large mass in the spleen, because even a benign tumor can rupture causing a hemoabdomen (free blood in the abdomen, and shock due to low blood pressure).
In these cases, we usually find out that the patient had indolent lymphoma in the spleen after it's been evaluated by the lab.
What is the prognosis for indolent lymphoma?
Patients are expected to live for years with indolent lymphoma. Most dogs with indolent lymphoma will die from other causes (not from lymphoma). The largest study on indolent lymphoma showed that the median survival (half lived longer and half shorter) was 4.4 years.
For dogs with splenic marginal zone lymphoma, the prognosis is influenced by how the dog feels at diagnosis.
If they feel sick at diagnosis and undergo splenectomy (removal of the spleen), they live an average of 309 days according to one study. If they feel normal at diagnosis and undergo splenectomy, they live an average of 1,153 days (3.2 years).
The average survival for dogs with T zone lymphoma (according to one study) is 33.5 months.
If you think your dog might have an indolent lymphoma and your primary care provider is not able to make a definitive diagnosis, get a second opinion from an oncologist or ask your vet if they'd be willing to call a local oncologist.
It's important to have an accurate diagnosis so you have a clear picture on your dog's prognosis as well as whether treatment is indicated or not.
Have questions about this article? Reach out!
Dr. Lori Cesario
Board Certified Veterinary Oncologist
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