In addition, at the transcriptome, proteome, and metabolome levels, the pattern in the heatmaps showed interpatient heterogeneity within HER2-low breast cancers, and there were more differences between HER2 1+ tumors and HER2 2+ tumors in the HR-negative subgroup than in the HR-positive subgroup (Fig. 1e and Supplementary Fig. S3). This evidence concerns the gene ERBB2 and breast cancer.