IDH1 mutations, FGFR2 fusions, MSI-H, NTRK fusions, BRAFV600E mutations and ERBB2 (HER2) have been classified as level I and three other aberrations as level III according to the most recent ESMO Guideline for Biliary Tract Cancer (Table 1) (16). The gene discussed is ERBB2; the disease is biliary tract cancer.