High Inter- and Intratumoral Variability of Ki67 Labeling Index in Newly Diagnosed Prostate Cancer with High Gleason Scores

Abstract

Background: The majority of studies investigating the role of Ki67 labeling index (LI) in prostate carcinoma (PC) focused on localized PC treated radically, where Ki67 LI is regarded as a prognostic marker. The relevance of Ki67 in advanced PC remains largely unexplored. While Gleason score is still one of the best indicators of clinical outcomes in PC, differences in progression-free survival and overall survival in patients with high Gleason scores suggest that additional factors are involved in tumor progression. Understanding the underlying mechanisms could help to optimize treatment strategies for an individual patient. Here, we aimed to determine the inter- and intratumoral distribution of Ki67 LI in patients with PC with high Gleason scores and to correlate Ki67 LI with the status of ERG, PTEN, and Bcl-2. Methods: Immunohistochemistry for Ki67, ERG, PTEN, and Bcl-2 was performed on core needle biopsies from 112 patients with newly diagnosed PC Gleason score 8, 9, and 10. Results: Using a cutoff of ≥10%, 17/112 cases (15%) had a homogeneously low and 95/112 cases (85%) a high Ki67 LI. 41% of cases showed intratumoral heterogeneity containing areas with low and high proliferation. There was no association between Ki67 LI and ERG, PTEN, or Bcl-2 status. Conclusions: Our data demonstrate major inter- and intratumoral variability of Ki67 LI in high-grade PC with a surprisingly low Ki67 LI in a subset of cases. Further studies are necessary to explore the molecular basis and potential clinical implications of a paradoxically low proliferation rate in high-grade PC.