MKI67 and breast cancer: These 2 clusters, one composed of ESR1-related genes, and the other composed of genes associated with proliferation like MKI67 and CCNB1 exhibited changes in the opposite direction in ER+/HER2- breast cancer patients (Figure 7D).To understand whether this pattern of correlation within the 18-gene list and Oncotype Dx is specific to ER+/HER2- breast cancer patients, we performed a similar Spearman correlation analysis in TCGA breast cancer data (Figure 8).