Evaluation of the Ki-67 labeling index on immediate pre-ablation biopsies as a predictive biomarker of local recurrence of colorectal cancer liver metastases.

The aim of this study was to evaluate if the Ki-67 labeling index (LI) on immediate pre-ablation biopsies of colorectal liver metastases (CLM) is associated with the presence of viable tumor cells in subsequent ablation zone biopsies and/or local tumor progression-free survival (LTPFS). Biopsies of CLM were performed before and after microwave ablation (MWA), as part of a prospective clinical trial between October 2013 and May 2019. Pre-ablation biopsy slides were examined for the Ki-67 LI using light microscopy. Ablation zone biopsy specimens were evaluated for the presence of viable tumor using hematoxylin-eosin and immunohistochemistry. Differences in CLM Ki-67 LI between positive and negative for viable tumor ablation zone biopsies were assessed using the Mann-Whitney U test. Biopsy, tumor and margin data were evaluated as predictors of LTPFS using Kaplan-Meier/Cox methods. Thirty-four patients with 48 CLM underwent biopsy before and after MWA. Sufficient tissue for Ki-67 labeling was obtained in 43/48 (89.6%) CLM. Viable tumor cells were detected in 11 ablation zones (22.9%). There was no significant difference in the CLM Ki-67 LI between the positive and negative for viable tumor ablation zones (mean: 69.2% vs. 64.3% respectively, p = 0.4). Adequate ablation zone margins (> 5 mm; p = 0.029) and negative ablation zone biopsies (p = 0.009) were significant predictors of longer LTPFS.