The Reliability of Assessment of Ki-67 Expression on Core Needle Biopsy and the Surgical Specimens of Invasive Breast Cancer: Comparison of Local Pathologists’ Assessment and Central Review

Purpose: The aim of this study was to assess the reliability of Ki-67 expression on core needle biopsy (CNB) and the surgical specimens of invasive breast cancer. We examined the concordance rate of Ki-67 expressions, hormone receptors, and human epidermal growth factor receptor 2 (HER2) status from a CNB with from a surgery in invasive breast cancer. Methods: A retrospective study was conducted on a clinical database of patients who underwent surgery for early breast cancer. Of these, 193 patients who underwent CNB before the surgery were enrolled. A cut-off value of 20% was used for Ki-67-positive criteria. Expression of estrogen receptor (ER), progesterone receptor (PgR), and HER2 were examined and compared with that of Ki-67. To evaluate discordance between the pathologists’ earlier assessments, we re-examined Ki-67 expression among the Ki-67 discordant group in a central laboratory. Results: The concordance rate for Ki-67 expression between the two specimen types was 77.7%, which was significantly lower than that for ER, PgR, and HER2 expression (95.9%, 88.1%, and 91.6%, respectively). The concordance rate for re-examined Ki-67 expression among the Ki-67 discordant group improved to 93.8% and was not significantly different from that for the other receptors. Conclusion: The concordance rate for Ki-67 expression between biopsy and surgical specimens was significantly lower than that for ER, PgR, and HER2 expressions, but re-examination of Ki-67 expression in a central laboratory revealed no significant difference among the receptors, suggesting the need for standard pathological assessment of Ki-67 expression for clinical use as a predictive marker of breast cancer.