DETERMINATION OF PROLIFERATIVE ACTIVITY IN CANINE LEUKEMIAS BY FLOW CYTOMETRY

Background: Nuclear antigen Ki67 is widely used as a prognostic indicator in many human tumors, while in veterinary medicine only few studies on solid tumours exist and no dataconcerningleukemias are present. Objective: To evaluate Ki67- positive cells in peripheral blood samples fromleukemic dogs by flow cytometry. Methods: 21 canine leukemias were evaluated. Based on clinical aspects, CBC, immunophenotype and cytologic features, leukemias were grouped as acute lymphoblastic (ALL, n=2), acute myeloblastic (AML, n=4), acute undifferentiated (AUL, n=3), chronic lymphocytic (CLL, n=8) and CLL/lymphoma complex (n=3). EDTA blood samples were labeled with Ki67-FITC (clone MIB-1) with a rapid fixation/ permeabilizationmethod using methanol.Proliferative activity was expressed as percentage of Ki67-positive cells. Results: Percentage of Ki67-positive cellswas significantly higher in acute than in chronic leukemias (P<0.01).In particular, decreasing values were recorded in AML, ALL, AUL and CLL with statistically significant difference between AML and CLL (P<0.05).B-CLL presented higher proliferative activity compared with T-CLL (13% and 4.8%, respectively), although without statistical significance.No differences between aberrant and non-aberrant immunophenotypes were detected among CLL. Conclusion: The higher proliferative activity recorded in acute canine leukemiascompared with chronic leukemiasconfirms the role of Ki67 antigen as areliable indicator of biological behavior.A larger series of samples is neededto check for differences between immunophenotypesamong AML, ALLand CLL. Follow-up informationwill help determine if Ki67 could be used to provide prognostic information.