Class II major histocompatibility complex expression and cell size independently predict survival in canine B-cell lymphoma

Background: Class II major histocompatibility complex (MHC) is an independent predictor of outcome in human B‐cell lymphoma. We assessed class II expression together with other markers for their impact on prognosis in canine B‐cell lymphoma. Hypothesis: Low class II MHC expression, large cell size, and expression of CD34 will predict a poorer outcome in canine B‐cell lymphoma. Expression of CD5 and CD21 on tumor cells also may be associated with outcome. Animals: One hundred and sixty dogs with cytologically confirmed lymphoma. Methods: Patient signalment, treatment type, and flow cytometry characteristics were analyzed for their influence on outcome. A multivariable predictive model of survival was generated using 2/3 of the patients and validated on the remaining 1/3 of the dataset. Results: Class II MHC expression had a negative association with mortality and relapse. Treatment type also influenced relapse and mortality, whereas cell size and patient age was only associated with mortality. CD34, CD21, and CD5 expression was not associated with disease outcome. The constructed model performed variably in predicting the validation group's outcome at the 6‐month time point. Conclusions and Clinical Importance: Low levels of class II MHC expression on B‐cell lymphoma predict a poor outcome, as in human B‐cell lymphoma. This finding has implications for the use of dogs to model human lymphomas. Class II expression, cell size, treatment, and age can be combined to predict mortality with a high level of specificity.