The correlation between Ki 67 and Oncotype Dx on HR+, HER2- early breast cancer management: Insights of molecular testing.

Abstract

e12546 Background: Elevated Ki-67 expression serves as an indicator of tumoral proliferation in breast cancer (BC) and is used in Ecuador for survival estimation, recurrence risk assessment, and guiding chemotherapy decisions. The Oncotype DX Breast Recurrence Score (ODX RS) is a validated 21-gene assay for hormone receptor-positive, HER2-negative invasive BC. It predicts chemotherapy benefits and the risk of distant recurrence over 10 years and is a mortality indicator. ODX RS has the potential to reduce the need for chemotherapy, alleviate financial burdens, and enhance clinical outcomes. Despite conflicting evidence on the significance of Ki-67 in the ODX RS, there is a lack of exploration within Latin populations. This study aims to compare the correlation of immunohistochemical (IHC) measured Ki-67 to the ODX RS in the Ecuadorian population. Methods: A retrospective analysis included women with early BC who underwent ODX RS testing in Ecuador from May 2020 to January 2023. Inclusion criteria: early BC (T1-T3/N0-N1a); IHC estrogen receptor (ER) positive; HER2 negative; and availability of tumor size, grade, lymph node status, and Ki67 proliferation index data. Exclusion criteria: patients with recurrent BC, incomplete pathology, or lacking IHC data. Patients were categorized into low (≤5%), intermediate (6%–29%), and high Ki67 expression groups (≥30%). Using the statistical software SPSS, the correlation between ODX scores and Ki-67 expression was analyzed using Pearson’s correlation coefficient. For risk stratification groups, Spearman's correlation was employed. Results: Among 77 patients undergoing Oncotype DX testing, 64 (with a mean age of 55) met the inclusion criteria. Eighty-six percent of cases were invasive ductal carcinomas (IDC). Seventeen percent exhibited low Ki-67 expression, 61% intermediate, and 20% high. No statistically significant correlation was found between IHC Ki-67 expression and ODX RS (r=0.051; p=0.69), neither when stratified by categories (r=0.086; p=0.50). A subanalysis based on risk categories showed 82% correspondence in the low Ki-67 group, 18% in the intermediate group, and 31% in the high Ki-67 group. No significant correlation was observed when stratified by histological types (invasive ductal carcinoma and invasive lobular carcinoma), nor by sample origin (core biopsy, excisional biopsy). Conclusions: There was no correlation between IHC Ki-67 expression and ODX risk scores in this study involving Ecuadorian patients. Our findings emphasize that IHC Ki-67 expression should not be the sole determinant for guiding therapeutic decisions and predicting recurrence in early breast cancer.[Table: see text]