European canine lymphoma network consensus recommendations for reporting flow cytometry in canine hematopoietic neoplasms

Multicenter flow cytometry proficiency testing of canine blood and lymph node samples

BACKGROUND

Flow cytometry (FC) is used increasingly in veterinary medicine for further characterization of hematolymphoid cells. Guidelines for optimizing assay performance and interpretation of results are limited, and concordance of results across laboratories is unknown.

OBJECTIVES

This study aimed to determine inter-investigator agreement on the interpretation of FC results from split samples analyzed in different laboratories using various protocols, cytometers, and software; and on the interpretation of archived FC standard (FCS) data files contributed by the different investigators.

METHODS

This was a multicenter observational cross-sectional study. Anticoagulated blood or lymph node aspirate samples from nine client-owned dogs were aliquoted and shipped to participating laboratories. Samples were analyzed with individual laboratory-developed protocols. In addition, FCS files from a set of separate samples from 11 client-owned dogs were analyzed by participating investigators. A person not associated with the study tabulated the results and interpretations. Agreement of interpretations was assessed with Fleiss' kappa statistic.

RESULTS

Prolonged transit times affected sample quality for some laboratories. Overall agreement among investigators regarding the FC sample interpretation was strong (κ = 0.86 ± 0.19, P < .001), and for specific categories, ranged from moderate to perfect. Agreement of the lymphoproliferation or other leukocyte sample category from the analysis of the FCS files was weak (κ = 0.58 ± 0.05, P < .001).

CONCLUSIONS

Lymphoproliferations were readily identified by FC, but identification of the categories of hematolymphoid neoplasia in fresh samples or archived files was variable. There is a need for a more standardized approach to maximize the enormous potential of FC in veterinary medicine.

Dogs with Acute Myeloid Leukemia Have Clonal Rearrangements in T and B Cell Receptors

Clonality testing for rearrangements in the complementarity-determining region 3 of the immunoglobulin heavy chain of B lymphocytes (B cell receptor) and the T cell receptor of T lymphocytes helps distinguish between clonal and non-clonal expansions of lymphocytes. There are rare reports of clonally rearranged T and B cell receptors in dogs with acute myeloid leukemia (AML). Our objective was to determine the frequency of clonally rearranged T and B cell receptors in dogs with AML. Archived slides from historical cases of AML (from January 2010 to June 2013) and slides or liquid specimens [blood, bone marrow (BM), body cavity fluid, or tissue aspirates] from cases of AML diagnosed between June 2013 and February 2017 were used in the study. A diagnosis of AML was made on the basis of more than 20% immature neoplastic cells ("blasts") in blood, BM, or extramedullary tissues, displaying features of myeloid differentiation. Myeloid differentiation was based on a combination of morphologic criteria, positive flow cytometric labeling for surface antigens typical of myeloid origin (e.g., CD11b, CD11c, CD14 with a general lack of expression of T or B cell markers), or positive cytochemical staining reactions for myeloid-associated enzymes (e.g., alkaline phosphatase, chloroacetate esterase). There were 63 cases of AML diagnosed during this period; however, slides or liquid specimens with sufficient DNA for testing were only obtained from 25 dogs. Affected dogs represented various breeds and were a median of 8 years old, with more male (64%) than female (36%) dogs. Common clinical signs were peripheral or internal lymphadenopathy (10/25 dogs, 40%) and hepatomegaly or splenomegaly (10/25 dogs combined, 40%). Typical hematologic findings were bi- or pancytopenia (23/25 dogs, 92%), with circulating blasts (21/25, 84%). Solitary clonal (4 B cell, 6 T cell) and biclonal (6 B and T cell) rearrangements in B or T cell receptors were found in 16 dogs (64%). Our results indicate that dogs with AML can have a high frequency of clonally rearranged T or B cell receptors, including biclonality, and clonality testing should not be used as a tool to distinguish between acute leukemia of myeloid or lymphoid origin.

Canine Lymphoma, More Than a Morphological Diagnosis: What We Have Learned about Diffuse Large B-Cell Lymphoma

Diffuse large B-cell lymphoma (DLBCL) is the most common canine aggressive B-cell lymphoma worldwide, and new recent molecular approaches have shown that DLBCL constitutes a heterogeneous tumor that cannot be unraveled by morphology and immunophenotype. DLBCL behaves aggressively, typically progressing over a short period of time, and the therapy response may be difficult to be predicted. Recently, the rate of bone marrow infiltration by flow cytometry has been demonstrated to be prognostic, but more sensible markers are needed. As the clinical behavior is different, there is vast clinical and basic research devoted to identifying prognostically or biologically distinct DLBCL subgroups. Transcriptomic analysis by gene expression profile, copy number variations by array comparative genomic hybridization and epigenetic perturbations have tentatively described this heterogeneity. Molecular subgroups using oncogenic pathways and target genes have also been correlated to different outcome in a small number of cases. The objectives of this review are to summarize the current knowledge on the biology, clinical, and pathological characteristics of canine DLBCL. To date, DLBCL probably is the most investigated tumor in veterinary medicine, and its relevance as spontaneous model for human DLBCL has been confirmed by these studies. In future, these discoveries will ultimately lead to a better understanding of the underlying disease mechanisms, possibly translating into more effective therapeutic strategies.

Lymphoid Neoplasia: Correlations Between Morphology and Flow Cytometry

Cytology is commonly used to diagnose lymphoma and leukemia. Frequently, a diagnosis of lymphoproliferative disease can be obtained via cytology, and some of the common subtypes of canine lymphoma and leukemia can have characteristic cytologic features. Flow cytometry is a critical tool in the objective diagnosis and further characterization of lymphoma and leukemia. Features of the immunophenotype, such as expression of certain cell surface proteins or cell size, can provide important prognostic information. This review describes the cytologic features, flow cytometry immunophenotype, and immunophenotypic prognostic information for 6 major types of canine lymphoma and leukemia.