Lymphoma is a cancer of lymphocyte cells, and while the more common kinds of lymphoma affect average sized cells, indolent lymphoma is typically characterized by affecting small lymphocytes. These small lymphocytes usually lead to a low mitotic index (meaning: the pace that the cancer cells reproduce is slower) and a slow clinical course of progression.1
Unlike the more common lymphomas, indolent variations can take longer before they affect the dog’s quality of life due to the slow progression, and some dogs will only have a single lymph node affected or the cancer is contained to the spleen alone.
There are a few different variations on what an indolent lymphoma can lead to in terms of classification, as with any kind of cancer, there are some variations that are easier to manage and have better prognoses than others. While some dogs may not be affected by the development of indolent lymphoma, others may develop a second malignancy or a progression into a large-cell or high-grade lymphoma known as Richter’s syndrome.1
The most common subtype seen in dogs with indolent lymphoma is T-zone lymphoma (TZL), a subcategory that makes up about 60% of all cases of indolent lymphomas. As the name suggests, T-zone lymphoma is a T-cell lymphoma type. T-cell lymphomas have a tendency to be more aggressive and fast acting than B-cell. However, T-cell lymphoma is associated with the longest median survival times of all indolent lymphomas.1
The next most common type of indolent lymphoma is marginal zone lymphoma (MZL), which has a B-cell origin. Marginal zone lymphoma typically occurs in either the lymph nodes or the spleen, which is seen more commonly. When MZL presents in the spleen it often has a great response to having the spleen removed as the only treatment necessary.2
While uncommon, these two lymphomas also fall under the category of indolent lymphomas. Follicular lymphoma (FL) are B-cell lymphomas that behave very similarly to atypical lymphoid hyperplasia. This requires careful morphological assessment aided by molecular clonality determination. Unfortunately, because FL is so uncommon there is not enough data covering what is to be expected in terms of the best treatment options and prognosis.3
Mantle cell lymphoma (MCL) is another B-cell lymphoma type that develops more frequently in the spleen than in the nodes. However, its occurrence in dogs is extremely rare (<2%). There is no conclusive data that determines the outcomes of treatment though it has been seen more anecdotally that treatment leads to a relatively good survival time.4
Diagnosing indolent lymphoma types can be slightly more complicated than diagnosing more common lymphomas. For a lot of dogs with indolent lymphoma, there won’t be many signs or symptoms that something is wrong leading to the necessity to be diagnosed. However, for some dogs, a swollen lymph node will draw the attention of a vet.
The exact number of canine indolent lymphoma cases is unknown, though the tumors are not rare and may have been underdiagnosed. Often, indolent lymphomas can be mistaken for lymphoid hyperplasia or a reactive lymph node through a fine needle aspirate (FNA) which is the first step in diagnosing many different afflictions of the lymph nodes.5
Because the affected cells are smaller than what would normally be found for high-grade lymphomas, a larger biopsy may be necessary. Taking a whole node or large wedge-shaped biopsy that incorporates a larger expanse of the lymph node can give some directional understanding of where the cells are in reference to the different parts of the lymph node, as well as where the cells are being affected.
Interpretation of the tissue architecture by histopathology and immunohistochemistry is required for a diagnosis. Indolent lymphomas are classified by cell type through immunophenotyping—the same way that a standard lymphoma diagnosis would progress—to further diagnose the lymphoma.6
Symptoms for indolent lymphoma types can vary greatly both in intensity and consistency. Dogs will usually present generalized signs of something going on with their lymph nodes that can come and go, along with no clinical signs of illness. If there are clinical signs of illness they are usually very mild and non-specific.
The main signal that something may be wrong when a dog has indolent lymphoma is at least one enlarged lymph node or an enlarged splenic nodule (which can be identified through palpation or ultrasound).
Dogs that are impacted by indolent lymphomas will often be middle-aged to older and have no signs of the illness, and many in the early stages of their lymphoma will be able to go several months with a low response to, or no general need for, treatment.
From the information currently gathered, there are no known predispositions for indolent lymphomas, and neither sex nor breed has shown a significant relationship with the cancer. However, retrievers and terriers may be overrepresented in the data available.6
Treatment for indolent lymphomas changes on a case by case situation, as with treatment for any cancer.
For some dogs, treatment will not be entirely necessary until something changes after the diagnosis. Veterinarians consider this “watchful waiting” and it is usually the method chosen for dogs with lymphoma detected in a very early phase.2
Some B-cell lymphomas, however, may progress into high-grade lymphomas with little warning prior to the advancement, in which case they will need to be treated the same way a high-grade lymphoma would be, with a multi-agent chemotherapy protocol (like CHOP).7
Currently, there is not a consensus among the veterinary oncology world as to the best protocol for treatment in cases of indolent lymphoma. For asymptomatic cases treatment can go from simple monitoring to the use of steroid treatments (prednisone) to a multiagent chemotherapy treatment, depending on the potential threat the cancerous cells pose.
When “watchful waiting” is the treatment plan, it often involves measuring and recording all developments from lesions on the skin to performing chest radiographs and abdominal imaging, as well as performing cytology through fine needle aspirates on organs that the cancer can spread to (the liver or spleen if not originally impacted).
When an indolent lymphoma shows no sign of spread outside of the impacted single lymph node or spleen, surgical removal of the affected area may be the most efficient and effective treatment for that particular case. Some surgical removals won’t even need the addition of chemotherapy after the procedure to have prolonged control of the condition.7
Indolent lymphoma is a relatively new classification for lymphoma in dogs and therefore needs more time to gain confident prognosis data and treatment expectations. However, from the information gathered at this time there are generally optimistic expectations for prognoses in a majority of cases.8
Many indolent lymphoma cases have a long survival time with little to no chemotherapy. In fact, many cases of indolent lymphoma don’t impact noticeably on the dog’s quality of life or survival times.
Median survival times for indolent lymphomas has been reported to be as long as 4.4 years.
However, should an indolent lymphoma case advance into high-grade lymphoma, or should the indolent lymphoma progress into the late stages and behave more like a high-grade lymphoma, survival times will change to reflect that.1 The prognosis of advanced indolent lymphoma—for example, an aggressive B- or T-cell—does not appear to be appreciably different from that of aggressive disease.
If your dog has been diagnosed with an indolent or standard lymphoma, there’s no reason to just hope for the best when it comes to treatment.
With the advancements in technology and oncology medicine that ImpriMed has built, we are able to help your veterinary oncologist find the best treatment plan possible for your pet on an individual basis.
Using our state-of-the-art labs and a giant (and still growing) database of information we are able to take your dog’s live cancer cells and develop a Personalized Prediction Profile to help you and your vet know the right drugs and dosages to use to find the most efficient treatment possible on the first try.