HER2 Pathway in Biliary Tract Cancer: A Snapshot of the Current Understanding and Future Directions.

Biliary tract cancers (BTCs) are a wide class of malignancies with dismal prognosis. The therapeutic scenario of metastatic BTCs has profoundly changed during recent years. The combination of cisplatin-gemcitabine plus immunotherapy is currently the gold standard in the first line. The more extensive comprehension of the mechanisms at the basis of BTCs and the identification of several molecular alterations has led to the introduction of target-directed therapies in the second line and beyond that have expanded the therapeutic armamentarium alongside the standard FOLFOX regimen, and for the near future, the results of some trials with targeted therapies in first line are expected. HER2 represents a promising therapeutic target detected in BTCs, being overexpressed in approximately 15-20% of cases, with a strong predilection for gallbladder carcinoma and extrahepatic cholangiocarcinoma, although a small proportion of HER2 overexpression can be detected even in intrahepatic cholangiocarcinoma. The efficacy and safety of different HER2 inhibitors have been investigated in several studies in the second line and beyond with encouraging results. This comprehensive review is intended to provide a summary of existing evidence and future perspectives on HER2 altered BTCs.