New research evaluates flow cytometry and PARR as diagnostic support for feline lymphoma

Feline lymphoma can be a challenging disease to diagnose for many reasons. According to Ira Gordon, DVM, DACVR-RO, radiation oncologist and former specialty practice owner, much of the challenge with diagnosing lymphoma in cats has to do with its variability in presentation. Whereas the most common clinical presentation in dogs with lymphoma is peripheral lymphadenopathy, Gordon reports that cats rarely present this way. Instead, he said, “many cases of feline lymphoma arise in places that are difficult to sample or biopsy,” such as the gastrointestinal tract, the kidneys, and the mediastinum. Furthermore, many cases of feline lymphoma are small cell, making them difficult to differentiate from other non-neoplastic conditions based on cytology.  

ImpriMed, a biotechnology company pairing laboratory techniques with cutting edge artificial intelligence (AI), recently reported on their work to help mitigate some of these concerns. Published in the journal Veterinary Sciences in July 2024, their article describes flow cytometry and as a “reliable and useful method for characterizing feline lymphomas,” citing 82-90% concordance with cytology, which the researchers refer to as the gold standard (along with histology for solid tissue) for lymphoma diagnosis. 

Ilona Holcomb, PhD, ImpriMed’s Director of Bioscience, explains that the company’s original focus was canine lymphoma. Their aim was to improve diagnostic and prognostic capabilities for veterinarians through the combination of advanced laboratory techniques and “real world clinical outcome data” to train advanced AI models. This has included flow cytometry panels, PCR for antigen receptor rearrangement (PARR), and drug response predictions (powered by AI) to determine which chemotherapy drugs would work best for a given patient, a true “personalized medicine tool” according to Holcomb.  

These assays are also available for canine leukemias, and flow cytometry and PARR are now offered for characterization of feline lymphomas and leukemias.  

The benefits and limitations of flow cytometry and PARR  

Flow cytometry involves suspending cells in liquid, passing them through a laser-based light source and then measuring the resultant scattering of light to draw conclusions about the cells’ relative size (small, medium, or large), granularity, and subtype (or immunophenotype), namely B cell or T cell for lymphocytes.  

PARR involves extracting and amplifying cell DNA to look for antigen receptor genes that code for either immunoglobulins (in B cells) or T cell receptors (in T cells). Identifying a homogenous population of antigen receptor genes (also termed clonality) can help differentiate neoplasia from reactive lymphocytes and determine the difference between B cell and T cell lymphomas to provide important prognostic and treatment insight.  

A variety of sample types, including lymph node aspirates, blood samples, and solid tissue samples, can be used for flow cytometry and PARR, provided an adequate amount of the cells of interest are present in the given sample. In the case of lymph node aspirates, multiple aspirations may be needed to obtain a sufficient number of cells (typically about a million cells are needed according to Holcomb).  

Holcomb clarified that she considers flow cytometry paired with PARR to be diagnostic support tools, whereby they are used to complement the results obtained by cytology/histology. Gordon echoed this sentiment: “PARR or flow cytometry should not be used as stand-alone tests in screening or diagnosing lymphoma but are useful ancillary tests when initial diagnostics are inconclusive or incomplete.” He added that a subset of cats with lymphoma may benefit from the additional prognostic information gained from these tests, although more research is needed to identify which cases would fit in this category. 

Opportunities for further study and advancement  

While it is already commercially available for canine lymphomas and leukemias, ImpriMed’s drug response prediction technology for feline lymphoma and leukemia is still being refined. Their hope is that it will be as informative for the treatment of cats as it has been for dogs. One of the challenges with cats, Holcomb says, is that they tend to be treated with fewer chemotherapy drugs at a time when compared to dogs. This has created a challenge in building a robust database of real-world outcome data from which their AI algorithms can draw conclusions and make predictions.  

Holcomb also reports that it is more difficult to make prognostic predictions and treatment recommendations for medium or intermediate cell lymphoma. Whereas small cell and large cell lymphomas have more well-known prognostic indicators and evidence-based treatment recommendations that can be made, medium cell lymphoma is less understood. She hopes that with continued research and AI training, they will be better able to predict treatment outcomes for this uncommon lymphoma subtype. 

Encouragement from an oncologist 

It can be easy to get discouraged by what we don’t know and what we still have yet to accomplish in our understanding of lymphoma in cats. “It is clear that feline lymphoma encompasses many diseases rather than a single entity,” Gordon said. He also commented that veterinary medicine is lagging “far behind” human medicine in the ability to diagnose and characterize lymphoma in cats.  Flow cytometry and PARR, however, represent a “significant step forward,” Gordon added. And while there is much to still be learned, he argues that it’s important that we not be afraid to take advantage of new diagnostic tools, even in their earlier stages. “As with all novel medical products, it will take robust clinical use and additional research to maximize our knowledge and their value,” he said. “If we are too slow to adopt them, companies will take them off of the market and our patients will be unable to benefit from them.” 

Further reading: 

Prognostic Utility of the Flow Cytometry and Clonality Analysis Results for Feline Lymphomas 

Flow cytometry for feline lymphoma article in J Feline Med Surg 

Feline lymphoma: diagnosis, staging and clinical presentations 

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