Characterization and Ki67 cut-off evaluation in canine indolent T-zone lymphoma: epidemiological and immunohistochemical aspects

ABSTRACT This study aimed to characterize the epidemiological and immunohistochemical aspects of canine indolent T-zone lymphoma and to evaluate the Ki67 cut-off point for differentiating T-zone lymphomas from high-grade lymphomas using paraffin-embedded samples. A total of 39 indolent T-zone lymphoma samples were analyzed. Epidemiological data were gathered from the medical records of affected dogs, and the corresponding tissue samples underwent immunohistochemical analysis using anti-CD3, CD45, CD79a, and Ki67 antibodies. The epidemiological assessment revealed that the most affected breed was the Golden Retriever (44%), followed by the Shih Tzu (13%). The most frequently noted clinical alteration was generalized lymphadenomegaly (52%). Seven animals (30%) exhibited lymphocytosis at the time of diagnosis. Immunohistochemical staining for CD45 was negative in all samples, consistent with flow cytometry analyses. The Ki67 cell proliferation index in T-zone lymphomas ranged from 5% to 40%, with a mean of 13.32% (±7.49). A Ki67 cut-off value of 42.5% demonstrated 100% sensitivity and specificity for differentiating T-zone lymphomas from high-grade lymphomas, including high-grade T-cell lymphomas. The overall survival was 256 days (±179), with specific survival at 334 days (±226). However, 14 out of 23 animals remained alive at the conclusion of the study, which had a follow-up period extending to 565 days. The epidemiological profile of T-zone lymphoma in this study resembled that found in American research, with a high prevalence among Golden Retrievers. The absence of CD45 staining and the low Ki67 value can be utilized in routine practice to differentiate T-zone lymphomas from high-grade T immunophenotype lymphomas, as these conditions have distinct prognoses and treatment protocols.