Proliferation in Minimal Invasive Samples of Canine Lymphomas: Ki67 Index in Previously Stained Cytology and Paired Cell Blocks

Canine lymphoma (CL) is a heterogeneous neoplasm with varying prognoses, and Ki67 expression is a key marker for assessing tumor proliferation. This study aimed to compare Ki67 immunostaining in cytology smears (PSCS) and cell blocks (CBs) of canine lymphoma cases. Ki67 immunostaining was performed on 30 cases (26 nodal and 4 non-nodal) of CL, including B-cell, T-cell, and null-phenotype lymphomas. The Ki67 index was quantified manually using image analysis software as a support. The results showed Ki67 positivity in all CBs, with archival time affecting the antigenicity in PSCS, especially in samples older than two years. The Ki67 index in CBs of nodal CL were higher, and there was no significant agreement on Ki67 classification in PSCS and CBs. A univariate brief survival analysis was performed to preliminary evaluate the prognostic value of Ki67 in cytological samples. Ki67 indexes determined in cytology showed no significant association with survival. Cases of nodal CL with high Ki67 in CBs, if treated with chemotherapy, tended to survived longer (compared to those animals not treated with chemotherapy). These preliminary results showed that Ki67 immunostaining in CBs is more reliable for assessing CL proliferation and might offer predictive information. These findings highlight the potential of Ki67 quantification in CBs for supporting treatment decisions.