ERBB2 and cancer: Using this approach, Gevensleben et al. showed that the plasma cfDNA copy number ratio of HER2 to a reference gene had an AUC of 0.92 and that 64 % of patients with HER2-amplified cancer and 94 % of patients with HER2-nonamplified cancer displayed positive and negative predictive values of 70 % and 92 %, respectively [29].