Figure 1A shows rapid drops in CTC counts in responding patients. Using two dual-biomarker assays (EGFR/Ki-67 and HER2/PD-L1), four biomarkers were investigated. Figure 1B shows a cluster of CTCs positive for EGFR and Ki-67, and a single CTC positive for HER2 and PD-L1 from a patient with esophageal cancer. This evidence concerns the gene ERBB2 and esophageal cancer.