Intratumoral Heterogeneity of Ki67 Proliferation Index Outperforms Conventional Prognostic Factors in Hormone Receptor-Positive Breast Cancer

Abstract

Abstract Background Immunohistochemistry (IHC) for ER, PR, HER2, and Ki67 is used in breast cancer (BC) pathology to assess tumor properties and predict patient outcomes and therapy responses. Visual scoring of the IHC biomarkers by pathologists, apart from reproducibility issues, does not sufficiently account for the intratumoral heterogeneity (ITH), often a subvisual feature within the tumor tissue. It has been reported that the ITH indicators of IHC biomarker expression can provide independent prognostic value. In this study, we applied digital image analysis (DIA) and computational pathology methods to investigate the prognostic value of IHC ITH indicators in hormone receptor-positive (HR-positive) BC patients.Methods Whole slide images of surgically excised specimens stained for ER, PR, Ki67, and HER2 from 178 patients with a diagnosis of HR-positive invasive ductal carcinoma were used in the study. Digital tumor tissue segmentation and detection of biomarker-positive and negative cells were performed. The DIA-generated data were systematically subsampled by a hexagonal grid to compute Haralick’s texture indicators for ER, PR, Ki67, and HER2. Univariate and multivariable Cox regression analyses were performed to assess the prognostic significance of the IHC and ITH indicators in the context of clinicopathologic variables, including conventional assessment of the IHC results provided by pathologists.Results In multivariable analysis, the ITH of Ki67-positive cells, measured by Haralick’s texture entropy, emerged as an independent prognostic factor associated with worse overall survival (hazard ratio = 11.40, p-value = 0.021). Remarkably, the entropy representing the spatial disarrangement of tumor proliferation outperformed the proliferation rate per se established either by pathology reports or DIA. None of the clinicopathologic variables were selected as independent prognostic features in our dataset.Conclusions These results add to the evidence from previous studies that ITH of IHC biomarkers, in particular, ITH of Ki67 proliferation index, exceeds the informative value of Ki67% per se (both visual and digital) in HR-positive BC. The study further demonstrates the benefits of high-capacity DIA-generated data for quantifying the essentially subvisual ITH properties.