Validated cancer drivers such as ERRBB2, EGFR, and KRAS demonstrated high copy number versus mRNA expression correlation in the corresponding cancer types they regulate (ERBB2 r = 0.9 in breast cancer, EGFR r = 0.8 in lung adenocarcinoma, KRAS r = 0.9 in ovarian cancer) (Figure 3–4). Here, ERBB2 is linked to breast cancer.