Ki-67 versus MammaPrint/BluePrint for assessing luminal type breast cancer.

Abstract

e13673 Background: Ki-67 is widely used for risk stratification in patients with ER+/HER2- breast cancer. The multigene assay, MammaPrint/BluePrint (MP/BP) test, is validated as a good predictor of recurrence in patients with Luminal type breast cancer and a good tool of molecular subtyping classification. Previous study showed that MP/BP test was able to re-stratify 54% of patients with a Luminal-B pathological subtyping (PS) to a low-risk Luminal A-type group. But there is no study directly show the comparison between Ki67 and MP/BP test result. Here in this study, we compare Ki-67 with MP/BP test result in Chinese patients with luminal type breast cancer. Methods: Formalin-fixed, paraffin-embedded (FFPE) tumour samples or fresh tumour samples from 1008 eligible breast cancer patients were collected from 122 hospitals in China. Tumor RNAs were isolated from samples and analyzed using RNA sequencing technology. Ki-67 protein expression were assessed in FFPE tissue blocks by IHC. The pathology subtyping of patient was categorized based on the 2013 St. Gallen. Comparison of MP/BP result with Ki-67 IHC was performed. Concordance between subtyping by the MP/BP and PS was also evaluated. Results: Of 1008 patients with ER+/HER2- breast cancer, 640 were MP Low-Risk and 368 were MP High-Risk. MammaPrint index was significantly associated with Ki-67 expression (p < 0.001). Among the patients with Ki-67 value lower than 15%, 81.11% were MP Low-Risk, while 65.12% of patients with Ki-67 value between 15%-20% and 46.67% of patients with Ki-67 value between 21%-30% were MP Low Risk. Of the patients with Ki-67 value higher than 30%, 77.24% were MP High-Risk. Among the 453 patients with PS Luminal-A tumours, 77 (17%) were categorized as Luminal-B by MP/BP test. While among the 555 patients with PS Luminal-B tumours, 265 (48%) were categorized as Luminal-A by MP/BP test. Conclusions: Our results show that for the patients with low Ki-67 value ( < 15%) or high Ki-67 value ( > 30%), the risk prediction by MP test are mostly agree with Ki-67 IHC, while for the patients with intermediate Ki-67 value (15-30%), MammaPrint test may provide more information. And compare with the traditional pathological factors, MP/BP test can help to identify a large group of patient with low risk of recurrence.