The frequency of HER2 overexpression varies: approximately 20% in breast cancers (Swain et al., 2023), 5–30% in ovarian cancers (Chen et al., 2023), 7–8% in colorectal cancers (Ivanova et al., 2022), 0–82% in pancreatic cancers (Han et al., 2021), and 7.3–20.2% in gastric and gastroesophageal cancers (Guan et al., 2023). The gene discussed is ERBB2; the disease is breast carcinoma.