How Does Ki-67 Expression Vary Between Core Needle Biopsy and Surgical Specimens in Untreated Early-Stage Breast Cancer?

Ki-67 is a critical biomarker in early-stage breast cancer, influencing adjuvant treatment decisions in patients not receiving neoadjuvant therapy. Variations in Ki-67 between core needle biopsies (CNB) and postoperative specimens can complicate treatment planning. The aim of this study was to determine whether there is a significant difference in Ki-67 changes between CNB and surgical specimens in estrogen receptor (ER) positive, human epidermal growth factor receptor 2 (HER2) positive and triple negative (TNBC) breast cancer subtypes. Data from 184 nonmetastatic, operable breast cancer patients who did not receive neoadjuvant treatment were analyzed. Age, tumor size, axillary lymph node involvement, adjuvant therapy, and CNB and postoperative Ki-67 values were evaluated. In the overall group, a statistically significant increase of 4.26 units and 2.50 units in the median was observed between pre and post-surgery Ki-67 values (p< 0.05). Significant increases were found in HER2-positive (mean change +7.58 ± 18.46%, 95% CI: 7.16–14.65, p= 0.029) and TNBC (mean change +14.58 ± 14.68%, 95% CI: 12.13–18.10, p= 0.007) subtypes, while the hormone receptor (HR)-positive group showed no significant median change (mean change +2.89 ± 10.89%, 95% CI: -1.58–2.43). In conclusion, HER2-positive and triple-negative tumors demonstrated a significant post-biopsy increase in Ki-67, indicating higher proliferative activity following biopsy. In HR-positive tumors, Ki-67 remained stable, indicating its reliability as a treatment predictor without genomic testing. Keywords: Breast cancer, Ki-67 variability, Pathologic specimens, Adjuvant chemotherapy