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

## TL;DR

This study shows that measuring Ki67 in cell blocks provides more reliable prognosis for canine lymphoma compared to cytology smears.

## Contribution

The study demonstrates that Ki67 quantification in cell blocks can predict survival outcomes in canine lymphoma.

## Key findings

- Cell blocks provided more reliable Ki67 quantification than cytology smears.
- High Ki67 levels in cell blocks correlated with better survival in dogs treated with chemotherapy.
- Archival time affected antigenicity in cytology smears, especially in older samples.

## Abstract

Canine lymphoma is a common and serious cancer in dogs and predicting how it will progress is important for choosing the best treatment. This study focused on a protein called Ki67, which indicates how quickly cancer cells are proliferating. Herein, Ki67 was quantified in two lymphoma samples: cytology smears and samples resulting from a processing of the lymphoma cells into a tissue-like form—called cell blocks. They found that cell blocks provided more reliable results. Although both methods showed similar levels of Ki67, only the Ki67 quantification in tissue-like samples predicted survival outcomes. Dogs with high Ki67 levels in cell blocks if treated with chemotherapy tended to have a survival advantage. This suggests that testing for Ki67 in cell blocks could help veterinarians to make better treatment decisions, potentially improving the chances of survival of dogs with lymphoma. More research is needed to confirm these findings, but this study represents an important step toward using minimal invasive samples for a prognostic assessment of canine lymphoma.

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.