Clinical case of trastuzumab deruxtecan use in treatment of patient with metastatic HER2-positive breast cancer and failure to standard therapy

Currently oncologists have numerous anti-HER2 drugs available, the sequential use of which ensures long-term disease control in metastatic HER2-positive breast cancer. These drugs belong to various classes, including monoclonal antibodies, tyrosine kinase inhibitors, and antibody–drug conjugates, which feature a fundamentally new mechanism of action. In these conjugates, the cytostatic agent is linked to the monoclonal antibody via a special linker. This structure allows the monoclonal antibody (trastuzumab) to recognize targeted tumor cells (HER2-positive), bind to the HER2 receptor, and the antibody–receptor complex is then internalized into the cell. The active cytostatic agent is then released and exerts its effect directly on the tumor cell. One of the most effective conjugates to date is trastuzumab deruxtecan (T-DXd). It has been studied in numerous trials and demonstrated high objective response rates, with progression-free survival and overall survival significantly higher than with standard treatment options. This article presents a clinical case of the use of T-DXd as a sixth-line therapy in a patient with metastatic HER2-positive breast cancer involving the lungs and brain, who had failed to respond to previous treatments, a rare occurrence. As the disease progressed, the patient’s cough and shortness of breath worsened with standard treatments, forcing her to leave work and significantly impairing her quality of life. When brain metastases were detected, she was prescribed T-DXd, and for the first time after all treatments, positive dynamics in the lung tumor process were observed, leading to a significant improvement in her well-being.