Concurrent trastuzumab deruxtecan-induced interstitial lung disease and COVID-19 in the treatment of advanced breast cancer.

Patients with cancer are at an increased risk of developing coronavirus disease 2019 (COVID-19) infection. Trastuzumab deruxtecan (T-DXd) is an antibody-drug conjugate (ADC) against epidermal growth factor receptor 2 (HER2)-positive cancer, known to cause drug-induced interstitial lung disease (DILD), including drug-induced pneumonitis. A 60-year-old woman with breast cancer developed a fever during treatment with T-DXd and was diagnosed with COVID-19. The fever persisted for approximately 3 weeks, and chest computed tomography showed multiple consolidations with bilateral peripheral predominance. Since the clinical course was atypical for COVID-19 due to the long duration of the fever and the CT pattern was frequently seen in T-DXd-induced ILD, the patient was diagnosed with T-DXd-induced ILD, following which, prednisolone was started, leading to improvement in the symptoms and fading of shadows. Even in patients suspected of COVID-19 pneumonia, physicians should consider the possibility of DILD, particularly in patients undergoing cancer treatment.