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

Nodal small cell B-cell lymphoma subtypes in dogs cannot be distinguished by flow cytometry and information regarding treatment, prognosis, and outcome are limited.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).Forty-nine dogs with nodal small cell B-cell lymphoma, defined by80% CD21+ B-cells by flow cytometry and small-sized B-cells by forward scatter.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.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.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.