ERBB2 and cancer: Biomarkers including Claudin 18 isoform 2 (CLDN18.2), tumor human epidermal growth factor receptor 2 (HER2) amplification, programmed death-ligand 1 (PD-L1) protein expression, tumor mutational burden (TMB), neurotrophic-tropomyosin receptor kinase (NTRK) gene fusion, and rearranged during transfection (RET) gene fusion may also be screened for to guide treatment decisions, most commonly in the setting of inoperable locally advanced, metastatic, or recurrent cancers.