Are Biopsy Specimens Effective for Evaluating HER2 Expression in Extrahepatic Bile Duct and Gallbladder Cancer?

Biliary tract cancer has a poor prognosis, with systemic chemotherapies showing limited benefit. New therapeutic targets are urgently needed to improve the prognosis of biliary tract cancer. Since HER2-targeted therapies have shown promising results for biliary tract cancer, accurate assessment for HER2 status in biopsy samples, which are often the only diagnostic material available for inoperable lesions, is crucial. This study assessed HER2 expression in 108 samples (surgical specimens and biopsies) from 84 biliary tract cancer patients. HER2 IHC scores of 2+ (equivocal) and 3+ (overexpression) were observed in 11% (7/65 specimens) and 9% (6/65 specimens) of biopsy specimens, and 7% (3/43 specimens) and 7% (3/43 specimens) of surgical specimens, respectively. The HER2 concordance rate between matched biopsy and surgical specimens was 75%. The results suggest that HER2 assessment in biopsies may reliably predict HER2 status across the tumor, supporting treatment decisions. However, the study acknowledges certain limitations, including the need for additional in situ hybridization tests in lesions of ambiguous HER2 overexpression. In conclusion, the HER2 status on biopsy specimens may reflect the HER2 status of the whole lesion and could be used to select suitable patients for neoadjuvant HER2-targeted therapy.