Breed Distribution and Clinical Characteristics of B Cell Chronic Lymphocytic Leukemia in Dogs

Abstract

Background: B-cell chronic lymphocytic leukemia (B-CLL) is the most common hematopoietic malignancy in humans in the developed world and the primary risk factor is genetic. Dogs also develop B-CLL, but there is no systematic description of the disease in dogs. Understanding the epidemiology of B-CLL in dogs may help practitioners recognize the disease and position the dog as a model for future genetic studies.

Objectives: To describe B-CLL presentation in dogs, its clinicopathologic findings, and breed predisposition.

Animals: Four hundred and ninety-one dogs with B-CLL and 5,673 control dogs with suspicion of a lymphoproliferative disorder (LPD).

Methods: Retrospective cross-sectional study of dogs for which samples were submitted to the Colorado State University Clinical Immunology Laboratory for immunophenotyping between 2010 and 2014. To assess breed predilection, dogs with B-CLL were compared to those with suspicion of other LPDs using logistic regression.

Results: The median age was 11 years with no sex predilection. Half of the dogs presented with peripheral lymphadenopathy or splenomegaly and 26% had anemia. Eleven small-breed dogs had significantly increased odds of B-CLL. In addition, English Bulldogs had an increased risk and a unique presentation: these dogs were diagnosed at a median of 6 years and expressed lower class II MHC and CD25.

Conclusions: B-cell chronic lymphocytic leukemia is overrepresented in small-breed dogs. Future genetic studies of these breeds may identify genetic risk factors. The unique presentation of English Bulldogs provides evidence of multiple forms of this disease. Additional studies are necessary to determine whether presenting signs are associated with survival.

Keywords: Dog; Epidemiology; Immunophenotyping; Leukemia; Lymphoma; Oncology.

Figure 1

Odds ratios and 95% confidence intervals comparing B‐CLL among each breed to all other lymphoproliferative disorders, using mixed breeds and Labrador Retrievers as a reference. Only breeds with at least 30 overall submissions were considered (37 breeds). Twelve breeds had significantly increased odds of B‐CLL when compared to both mixed breeds and Labrador Retrievers: Dachshund, Pomeranian, Cairn Terrier, Bichon Frise, English Bulldog, Boston Terrier, Jack Russell Terrier, Maltese, Yorkshire Terrier, Shih Tzu, Cocker Spaniel, and Pit Bull. In addition, six breeds had significantly decreased odds of B‐CLL compared to both mixed breeds and Labrador Retrievers: German Shepherd, Golden Retriever, Rottweiler, Welsh Corgi, Bernese Mountain Dog, and Standard Poodle.

Figure 2

Median age (A), percent of CD25‐positive B‐cells (B), and median class II MHC expression (C) were compared for the top six breeds with significantly increased odds of B‐CLL (Shih Tzu, Pit Bull, Cocker Spaniel, English Bulldog, Jack Russell Terrier, Dachshund) versus mixed‐breed dogs. Significant differences were noted for English Bulldogs and Shih Tzus with B‐CLL, and are displayed in the figure. Compared to mixed‐breed dogs, English Bulldogs presented at a significantly younger age, with lower percent of CD25‐positive B‐cells, and decreased class II MHC expression. Shih Tzus had no significant difference in age or class II MHC expression, but were significantly less likely to have a low percentage of CD25‐positive B cells.