Ki67 Assessment By qRT-PCR In OncotypeDx® Breast Recurrent Score®: Low Correlation With Immunohistochemistry Assessment of Ki67 And Prognostic Impact of Ki67 RNA Level of Expression.

Breast cancers expressing high levels of Ki67 are associated with poor outcomes. Oncotype DX® test was designed for ER+/HER2- early-stage breast cancers to help adjuvant chemotherapy decision by providing a Recurrent Score® (RS®). RS® measures the expression of 21 specific genes from tumor tissue, including Ki67. The primary aim of this study was to assess the agreement between Ki67RNA obtained with Oncotype DX® RS® and Ki67IHC. Other objectives were to analyze the association between the event free survival (EFS) and the expression level of Ki67RNA; and association between RS® and Ki67RNA.Herein, we report a low agreement of 0.24 by Cohen’s kappa test between Ki67IHC and Ki67RNA in a cohort of 98 patients with early ER+/HER2- breast cancers. Moreover, Ki67RNAhigh tumors were significantly associated with the occurrence of events (p=0.02). On the other hand, we did not find any association between Ki67IHC and EFS (p=0.25).We observed of low agreement between expression level of Ki67RNA and Ki67 protein labelling by IHC. Unlike Ki67IHC and independently of the RS®, Ki67RNA could have a prognostic value. It would be interesting to better assess the prognosis and predictive value of Ki67RNA measured by qRT-PCR. The Ki67RNA in medical routine could be a good support in countries where Oncotype DX® is not accessible.