It is used to treat adult patients with unresectable or metastatic HER2-positive breast cancer, unresectable or metastatic NSCLC with activating HER2 (ERBB2) mutations, and those with locally advanced or metastatic HER2-positive gastric or gastroesophageal junction adenocarcinoma who have previously undergone a trastuzumab-based regimen [110]. This evidence concerns the gene ERBB2 and gastroesophageal junction adenocarcinoma.