Risk factors associated with discordant Ki-67 levels between preoperative biopsy and postoperative surgical specimens in breast cancers

Purpose The Ki-67 labelling index is significant for the management of breast cancer. However, the concordance of Ki-67 expression between preoperative biopsy and postoperative surgical specimens has not been well evaluated. This study aimed to find the correlation in Ki-67 expression between biopsy and surgical specimens and to determine the clinicopathological risk factors associated with discordant values. Patients and Methods Ki-67 levels were immunohistochemically measured using paired biopsy and surgical specimens in 310 breast cancer patients between 2008 and 2013. ÄKi-67 was calculated by postoperative Ki-67 minus preoperative levels. The outliers of ÄKi-67 were defined as [lower quartile of ÄKi-67-1.5 ? interquartile range (IQR)] or (upper quartile + 1.5 ? IQR) and were evaluated according to clinicopathological parameters by logistic regression analysis. Results The median preoperative and postoperative Ki-67 levels were 10 (IQR, 15) and 10 (IQR, 25), respectively. Correlation of Ki-67 levels between the two specimens indicated a moderately positive relationship (coefficient = 0.676). Of 310 patients, 44 (14.2%) showed outliers of ÄKi-67 (range, -20 or 28). A significant association with poor prognostic factors was found among these patients. Multivariate analysis determined that significant risk factors for outliers of ÄKi-67 were tumor size >1 cm, negative progesterone receptor (PR) expression, grade III cancer, and age 35 years. Among 171 patients with luminal human epidermal growth factor receptor 2-negative tumors, breast cancer subtype according to preoperative or postoperative Ki-67 levels discordantly changed in 46 (26.9%) patients and a significant proportion of patients with discordant cases had 1 risk factor. Conclusion Ki-67 expression showed a substantial concordance between biopsy and surgical specimens. Extremely discordant Ki-67 levels may be associated with aggressive tumor biology. In patients with luminal subtype disease, clinical application of Ki-67 values should be cautious considering types of specimens and clinicopathological risk factors.