In the study of Chen et al., 71 samples from patients with stage III-IV BC were characterized for HER2 expression in both primary tumor and CTCs analyzed through the LiquidBiopsy system (Cynvenio LLC, Westlake Village, CA); CTCs were defined as HER2-positive based on HER2 immunofluorescence intensity ≥3.5 times higher than CD45 intensity (100% sensitivity and 99.9% specificity on cell lines experiments). The gene discussed is ERBB2; the disease is breast cancer.