Clinical outcome and Ki67 evaluation in dogs with nodal small cell B‐cell lymphoma diagnosed by flow cytometry

BACKGROUND: Nodal small cell B‐cell lymphoma subtypes in dogs cannot be distinguished by flow cytometry and information regarding treatment, prognosis, and outcome are limited. HYPOTHESIS/OBJECTIVES: Objectives were to describe outcome in dogs with nodal small cell B‐cell lymphoma diagnosed by flow cytometry and correlate clinical and laboratory data with survival. We hypothesized that B‐cell Ki67 expression measured by flow cytometry is associated with shorter progression free survival (PFS) and overall survival (OS). ANIMALS: Forty‐nine dogs with nodal small cell B‐cell lymphoma, defined by >80% CD21+ B‐cells by flow cytometry and small‐sized B‐cells by forward scatter. METHODS: Retrospective study reviewing treatment and outcome data extracted from medical records. Percentage of Ki67‐expressing B‐cells was measured by flow cytometry. Clinical, laboratory, and flow cytometry data were assessed for association with outcome. RESULTS: Median percentage of B‐cell Ki67 was 41% (range, 3%‐97%). Median PFS was 119 days and median OS was 222 days (n = 49). Among cases treated with CHOP‐based chemotherapy (n = 32), median PFS was 70 days, median OS was 267 days, and 50% of cases achieved complete response. Low percentage of B‐cell Ki67 (≤11%) was associated with prolonged OS by univariable analysis. Greater age, substage B, high B‐cell CD25 expression and low B‐cell CD21 and class II major histocompatibility complex expression by flow cytometry were independently associated with shorter OS. CONCLUSIONS AND CLINICAL IMPORTANCE: Most nodal small cell B‐cell lymphoma cases had aggressive disease. Low Ki67 expression can help identify cases with better prognosis. Age, substage, and flow cytometry variables are useful prognostic factors.