As a consequence of extensive gene expression profiling, first generation gene signature-based diagnostic tests (e.g., OncotypeDx® and MammaPrint®) have entered clinical diagnostics for patients with early-stage tumors that are non-amplified for ERBB2, the gene that codes for the human epidermal growth factor receptor 2 (i.e., HER2– breast cancers) [7]. This evidence concerns the gene ERBB2 and breast cancer.