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Objectives: Ki-67 labeling index (LI) is a crucial prognostic and predictive biomarker in breast carcinoma, but its clinical utility is limited by a lack of standardization in scoring methods. This study evaluates the hotspot, average, and tumor edge methods for Ki-67 LI assessment in core needle biopsies and resection specimens. Material and Methods: A combined retrospective and prospective observational study was conducted on 200 cases of primary invasive breast carcinoma. Ki-67 LI was determined using immunohistochemistry and counted through the three methods. Correlations with histological grade, estrogen receptor (ER), progesterone receptor (PR), and human epidermal growth factor receptor 2 (HER2) status were analyzed. Results: Mean Ki-67 LI was highest with the hotspot method (51.9% in biopsies, 50.5% in resections), followed by tumor edge (46.8%, 46.9%) and average (44.5%, 40.3%) methods ( P < 0.001 for inter-method differences). All methods correlated significantly with higher histological grades and negative ER/PR/HER2 status ( P < 0.001). Intraclass correlation coefficient values exceeded 0.9, indicating strong concordance, with hotspot and tumor edge methods showing the highest agreement. Categorization into low (<20%) and high (≥20%) Ki-67 groups revealed minimal differences in biopsies but a higher prevalence of low-Ki-67 tumors with the average method in resections ( P < 0.05). Conclusion: The hotspot method yields consistently higher Ki-67 LI and better concordance across specimen types.
Gill et al. (Mon,) studied this question.