P1-07-15: The Reliability of Ki-67 Expression Assessment Using Core Needle Biopsy and Surgical Specimens of Invasive Breast Cancer: Can Ki-67 Change Predict Benefits of Preoperative Endocrine Therapy?

Abstract

Abstract Background: The use of Ki-67 change as a predictive marker in breast cancer has been widely investigated in patients treated with preoperative endocrine therapy. It has been assumed that Ki-67 expression determined using core needle biopsy and surgical specimens of invasive breast cancer is concordant. Many studies have suggested the concordance of the results obtained using core needle biopsy and surgical specimens for expression of the estrogen receptor (ER), progesterone receptor (PgR), and human epidermal growth factor receptor type2 (HER2) status in early-stage breast cancer. However, there was few study to compare Ki-67 expression in the core needle biopsy and surgical specimens. We conducted a retrospective study of Ki-67 expression assessment between the two types of specimens to answer this question. Methods: A total of 269 patients underwent primary operations for early-stage breast cancer at Tokyo-West Tokushukai Hospital from August 2008 to May 2011. Among these patients, 169 patients who received core needle biopsy prior to operation were enrolled. Patients with ductal carcinoma in situ and those with neoadjuvant chemotherapy were excluded. A cutoff value of 20% was used for Ki-67-positive criteria. We also examined ER, PgR, and HER2 expression and compared it with Ki-67 expression. Statistical significance for concordance rates between the two types of specimens was evaluated by Wilcoxon t-test. To evaluate the consequence of formalin and genetic heterogeneity, parameters such as operative method and tumor size were analyzed by χ2 analysis. Results: The concordance rate between the two types of specimens for Ki-67 expression was 76%, and this was significantly lower than that for ER expression, which was 96%. The concordance rates for PgR and HER2 expression were 88% and 91%, respectively, and they were not significantly different from the rate for Ki-67 expression. 45 patients(34.6%) had received mastectomy in the Ki-67 concordant group, and 14 patients(34.1%) in the discordant group. 55 patients(42.0%) showed T2∼ tumor size in the concordant group, 13 patients(31.7%) in the discordant group. No significant differences of parameters such as operative method (mastectomy vs breast conserving surgery) and tumor size (T1 vs T2∼) were observed between the two patient groups. Conclusion: The reliability of Ki-67 concordance rate assessment using core needle biopsy specimens was significantly lower than that of ER expression. A standard pathological assessment of Ki-67 expression might be needed for the possible use of Ki-67 as a predictive marker for preoperative endocrine therapy. Citation Information: Cancer Res 2011;71(24 Suppl):Abstract nr P1-07-15.