The MKShi/ERSlo tumours had significantly higher CCNE1 mRNA expression than MKShi/ERShi tumours (p = 2.0 × 10−7) (Fig. 3c), and exhibited the highest CCNE1 mRNA expression among all ER+/HER2− tumours (Supplementary Fig. S3C). Here, ERBB2 is linked to neoplasm.