Population-based estimate for the correlation of the Oncotype Dx Breast Recurrence Score® result and Ki-67 IHC MIB-1 pharmDx in HR+, HER2−, node-positive early breast cancer

Background The United States Food and Drug Administration recently approved a Ki-67 immunohistochemistry (IHC) assay to identify patients with early breast cancer at high disease recurrence risk. The Oncotype Dx Breast Recurrence Score® assay has been validated in hormone receptor-positive (HR+), human epidermal growth factor receptor 2-negative (HER2−) invasive breast cancer (IBC) to predict chemotherapy benefit and distant recurrence risk, regardless of nodal status. This study assessed the correlation between Recurrence Score® (RS) results and the Ki-67 IHC MIB-1 pharmDx assay. Methods HR+, HER2−, N1 IBC samples with RS results were examined by Ki-67 IHC; 311 specimens were collected, including 275 without regard to RS (“unselected RS”) and 36 more with RS 26–100; 12 were lymph node negative upon pathology report review, and one had no Ki-67 score, leaving 262 unselected RS and 298 total samples. Spearman rank correlation was calculated using the unselected samples and a weighted rank correlation using all samples. A receiver operating characteristic (ROC) curve for predicting high RS (26–100) from Ki-67 was constructed. Results The Spearman rank correlation between Ki-67 and RS results was moderately positive (unselected RS samples: 0.396; 95% confidence interval [CI] 0.288–0.493; all samples: 0.394; 95% CI 0.294–0.486). While 71% of samples with RS 26–100 had Ki-67 ≥ 20%, 75% with RS 0–25 had Ki-67 < 20%. ROC area under the curve was 0.792 (95% CI 0.725–0.859). Conclusions The moderately positive correlation is consistent with previous analyses suggesting the Oncotype Dx® assay and Ki-67 IHC MIB-1 assay should not be used interchangeably in clinical practice.