Monitoring and management of interstitial lung disease/pneumonitis among patients with metastatic breast cancer treated with trastuzumab deruxtecan.

1036 Background: Trastuzumab Deruxtecan (T-DXd) was associated with an increased risk of interstitial lung disease (ILD)/pneumonitis (P) in metastatic breast cancer (mBC) patients (pts) in clinical trials, leading to ILD/P monitoring and management guidelines in the product label. This study aims to describe the monitoring and management of ILD/P during T-DXd therapy among US community oncology practices. Methods: Oncologists in the Cardinal Health Oncology Provider Extended Network (OPEN) participated in a cross-sectional survey on monitoring approaches for ILD/P among mBC pts. Participating physicians provided data from medical charts of up to 10 pts who were treated with T-DXd regarding presence of ILD/P symptoms, management, and outcomes of ILD/P symptoms. Results: Twenty-eight physicians from across the U.S participated and provided data on 149 T-DXd pts. Nearly all physicians reported they were monitoring ILD/P after T-DXd initiation by physical examination (n = 27), symptoms checklist (n = 25) and pulse oximetry (n = 23) at every visit, whereas fewer reported performing lung CT scan (n = 18), echocardiogram (n = 13), chest X-ray (n = 12), lung PET scan (n = 10), pulmonary function tests (n = 8) and diffusion testing (n = 7) on a less frequent basis. Among 149 T-DXd pts, 4 pts were diagnosed with ILD/P over an average T-DXd treatment duration of 5.5 months. All 4 cases initiated T-DXd treatment at 5.4mg/kg every 3 weeks, experienced ILD/P within the first 5 cycles of T-DXd, were diagnosed with lung CT scan and initially presented with Grade 2 symptomology (2 cases progressed to Grade 3). For both cases that remained as Grade 2, ILD/P completely resolved within 23 days. One case received IV methylprednisolone (1000mg daily; duration of therapy (DOT): 3 days) during hospitalization, oxygen therapy and T-DXd was permanently discontinued; whereas the other one received oral prednisone (started at 40mg daily and tapered to 5mg daily; DOT: 7 days) and T-DXd dose was held. For the two grade 3 cases, one received IV methylprednisolone (125mg daily; DOT: 7 days) during hospitalization, T-DXd dose was held, and ILD/P completely resolved within 11 days; whereas the other case received oral prednisone (started at 80mg daily and tapered to 5mg daily; DOT: 63 days), oxygen therapy, T-DXd was permanently discontinued, and ILD/P resolved with sequela within 46 days. Conclusions: ILD/P incidence in this small study sample of patients receiving T-DXd treatment was 2.7%. Although general awareness of ILD and routine screening by pulse oximetry and physical exam were common, management approaches for ILD/P were not always consistent with T-DXd prescribing information. Further physician education may be needed to improve appropriate management of ILD/P and outcomes for T-DXd pts.