Analysis of Adverse Events Associated with Trastuzumab Deruxtecan in Patients with Gastric and Breast Cancer: A Retrospective Study.

Trastuzumab deruxtecan (T-DXd) has displayed demonstrable efficacy and manageable toxicity in previously treated patients with advanced gastric and breast cancer, and it has been approved in Japan. However, there is a lack of data on the optimal management in clinical practice. Therefore, we assessed the adverse event (AE) profiles of T-DXd in patients with advanced gastric or breast cancer to provide guidance for appropriate management. This retrospective study was conducted at the Cancer Institute Hospital of the Japanese Foundation for Cancer Research. We reviewed the medical records of patients with advanced gastric or breast cancer who received T-DXd between May 2020 and December 2021. AEs occurring within the first three cycles of T-DXd were evaluated according to Common Terminology Criteria for Adverse Events version 5.0. Thirty-six patients were enrolled (gastric: n = 19, breast: n = 17). All 15 males had gastric cancer, whereas 4 and 17 females had gastric and breast cancer, respectively. Interstitial lung disease (ILD) occurred in five patients (14%), but no patients had severe ILD. Gastrointestinal (GI) toxicities, including nausea (61%), vomiting (22%), decreased appetite (33%), and diarrhea (39%), were the most common AEs. The incidence of GI toxicities did not differ by cancer type; however, nausea was significantly more common in females (81 vs. 33%; p < 0.01). T-DXd was safely administered in clinical practice in patients with previously treated advanced gastric or breast cancer. The management of GI toxicities is important in the clinical implementation of T-DXd.