The role of HER2 and therapy beyond the treatment of breast tumors

The role of HER2 and anti-HER2 therapy in breast cancers has been known since 1998. The second group of tumors to start using trastuzumab was gastric tumors in 2010. Several new therapeutic options have been developed, in addition to monoclonal antibodies, tyrosine kinase inhibitors, ADCs have been shown to be effective. HER2 is an emerging target in the target-therapy of gastrointestinal tumors. In addition to gastric tumors, the HER2 inhibition has an important role in the treatment of biliary carcinomas and colorectal tumors and has already entered our daily practice and will be the focus of this review. Trastuzumab deruxtecan is the first HER2 inhibitor tumor agnostic therapy (FDA) for patients with HER2 IHC3+ solid tumors, with high response rates, making it a new effective therapeutic option for patients for whom no other effective therapy is available. HER2 is not so rare and has been a known target for many years, making its inhibition with derux tecan the most exciting new option for tumor agnostic therapy. In addition to gastrointestinal tumors, its efficacy in lung cancers and gynecological malignancies should be emphasized. The determination of HER2 IHC will be necessary across a broad range of tumors in the future, based on the results of clinical trials. Another important issue to be clarified in the coming years is the efficacy of trastuzumab deruxtecan in HER2-low solid tumors.