ERBB2 and neoplasm: IHC staining revealed the tumor’s pulmonary origin and ruled out a prostate origin, and genetic testing identified a HER2 exon 20 mutation, which is associated with aggressive tumor behavior and poor prognosis (Friedlaender et al., 2022), while the Ki-67 proliferation index of 5% indicated moderate tumor cell proliferation, suggesting an active but not highly aggressive tumor growth rate.